Magnetic recording medium

Abstract

The purpose of the present invention is to improve the thermal stability of a magnetic recording medium. The present technology provides a magnetic powder including hexagonal ferrite particles containing Fe, Ba, Sr, and Nd, wherein the atomic ratio of Nd to Fe (Nd / Fe) is 0.0002-0.0050, and the atomic ratio of Sr to Ba (Sr / Ba) is 0.6-1.0. The magnetic powder may further include at least one selected from the group consisting of Ti, Mn, Zr, and Sn. The average plate diameter of the magnetic powder may be 8.0-20.0 nm. Furthermore, the average plate ratio of the magnetic powder (the ratio of the average plate diameter of the magnetic powder to the average plate thickness of the magnetic powder) may be 1.0-3.0.

Description

Magnetic recording medium 【0001】 This technology relates to a magnetic recording medium. 【0002】 Due to the development of the IT (information technology) society and the like, the demand for increasing the recording density of tape-shaped magnetic recording media as data storage media has been increasing. In tape-shaped magnetic recording media, in order to achieve high density, various magnetic powders have been studied. For example, hexagonal ferrite magnetic powder is used as the magnetic powder, and in order to meet the requirement of high recording density, the reduction of the particle size of the hexagonal ferrite magnetic powder is required. For example, Patent Document 1 discloses hexagonal ferrite magnetic powder having an average particle size in the range of 10 nm to 25 nm. 【0003】 Japanese Patent Application Laid-Open No. 2015-127985 【0004】 The main object of this technology is to improve the thermal stability of the magnetic recording medium. 【0005】 That is, this technology includes hexagonal ferrite particles containing Fe, Ba, Sr, and Nd, and the atomic number ratio (Nd / Fe) of Nd to Fe is 0.0002 or more and 0.0050 or less, and the atomic number ratio (Sr / Ba) of Sr to Ba is 0.6 or more and 1.0 or less. A magnetic powder is also provided. The magnetic powder may further contain at least one selected from the group consisting of Ti, Mn, Zr, and Sn. The average plate diameter of the magnetic powder may be 8.0 nm or more and 20.0 nm or less. The average plate ratio of the magnetic powder (the ratio of the average plate diameter of the magnetic powder to the average plate thickness of the magnetic powder) may be from 1.0 to 3.0. The average particle volume of the magnetic powder is 200 nm ３ or more and 1600 nm ３ or less. The crystalline magnetic anisotropy constant K of the magnetic powder ｕ is 2.20×10 ６ erg / cc or more and 2.70×10 ６ erg / cc or less. The thermal stability (K ｕ V ａｃｔ / k Ｂ T, K ｕ : Crystalline magnetic anisotropy constant of the magnetic powder, V ａｃｔ: Activation volume of magnetic powder, k Ｂ The Boltzmann constant (T: absolute temperature) may be 60 or greater. The Switching Field Distribution (SFD) of the magnetic powder may be 0.5 or greater and 1.5 or less. The H of the magnetic powder ｃ The coercivity may be between 2200 Oe and 2700 Oe. The saturation magnetization (σs) of the magnetic powder may be between 49.5 emu / g and 54.0 emu / g. The full width at half maximum (FWHM) Ha of the main peak of the SFD (Switching Field Distribution) curve of the magnetic powder may be 4000 Oe or less. The present technology also provides a magnetic recording medium having a magnetic layer containing magnetic powder, wherein the magnetic powder contains hexagonal ferrite particles comprising Fe, Ba, Sr, and Nd, the atomic ratio of Nd to Fe (Nd / Fe) is between 0.0002 and 0.0050, and the atomic ratio of Sr to Ba (Sr / Ba) is between 0.6 and 1.0. In the magnetic recording medium of this technology, the magnetic powder may further contain at least one selected from the group consisting of Ti, Mn, Zr, and Sn. In the magnetic recording medium of this technology, the average plate diameter of the magnetic powder may be 8.0 nm or more and 20.0 nm or less. In the magnetic recording medium of this technology, the average plate ratio of the magnetic powder (ratio of the average plate diameter of the magnetic powder to the average plate thickness of the magnetic powder) may be 1.0 or more and 3.0 or less. In the magnetic recording medium of this technology, the average particle volume of the magnetic powder is 200 nm. ３ 1600nm or more ３ The following may apply: The magnetic recording medium of this technology has a crystal magnetic anisotropy constant K. ｕ However, 2.75 x 10 ６ erg / cc or more 3.25×10 ６ It may be erg / cc or less. In the magnetic recording medium of this technology, the SFD (Switching Field Distribution) of the magnetic powder may be 0.5 or more and 1.5 or less. In the magnetic recording medium of this technology, H in the vertical direction ｃThe coercivity may be between 2500 Oe and 3500 Oe. In the magnetic recording medium of this technology, the full width at half maximum Ha of the main peak of the SFD (Switching Field Distribution) curve may be 5000 Oe or less. 【0006】 This is a perspective view showing an example of particle shape. This is a diagram showing an example of a TEM image of a magnetic layer. This is a diagram showing an example of a TEM image of a magnetic layer. This is a manufacturing process diagram illustrating an example of a method for manufacturing magnetic powder according to the first embodiment. This is a cross-sectional view showing an example of the configuration of a tape-shaped magnetic recording medium. This is a schematic diagram showing an example of the layout of a data band and a servo band. Figure 7A is an enlarged view showing an example of the configuration of a data band. Figure 7B is an enlarged view showing an example of a data track in a magnetic recording system. This is an enlarged view showing an example of the configuration of a servo band. This is a diagram showing the relationship between average particle volume and plate ratio in Experimental Example 1-1. This is a diagram showing the relationship between firing temperature and plate ratio in Experimental Example 1-2. This is a diagram showing the relationship between saturation magnetization σs and average particle volume. This is a diagram showing the relationship between average particle volume and coercivity Hc. Figure 13 shows the relationship between Nd addition amount and K ｕ V / K Ｂ This diagram shows the relationship between T and the firing temperature and coercivity H of the magnetic powder. ｃ This figure shows the relationship between the firing temperature of the magnetic powder and the square ratio Rs. This figure shows the relationship between the firing temperature of the magnetic powder and the saturation magnetization σs. This figure shows the results of XRD measurement of the fired body. This is an exploded perspective view showing an example of the configuration of a magnetic recording cartridge. 【0007】 The following describes preferred embodiments for implementing this technology. Note that the embodiments described below represent typical embodiments of this technology, and the scope of this technology is not limited to these embodiments. 【0008】 This technology will be explained in the following order: 1. Description of this technology 2. First embodiment (1) Composition of magnetic powder (2) Method for manufacturing magnetic powder 3. Second embodiment (1) Composition of magnetic recording medium (2) Description of each layer (3) Method for manufacturing magnetic recording medium 4. Third embodiment (1) One embodiment of a magnetic recording cartridge 5. Experimental example 【0009】In this specification, unless otherwise specified regarding the measurement environment in relation to the description of the measurement method, the measurement shall be performed under conditions of 25°C ± 2°C and 50% RH ± 5% RH. 【0010】 1. Description of this technology 【0011】 When hexagonal ferrite magnetic powder is used as the magnetic powder, the magnetic properties deteriorate as the hexagonal ferrite magnetic powder becomes smaller, and the thermal stability of the magnetic recording medium is likely to worsen. 【0012】 The inventors have discovered that even when the hexagonal ferrite magnetic powder is small, the addition of neodymium (Nd) makes it possible to control the plate ratio (shape magnetic anisotropy) of the magnetic powder and improve the magnetic anisotropy energy, and that when a magnetic recording medium is fabricated using the hexagonal ferrite magnetic powder, a magnetic recording medium with excellent thermal stability can be obtained. 【0013】 2. First Embodiment 【0014】 (1) Composition of magnetic powder 【0015】 The following describes a magnetic powder according to the first embodiment of this technology. The magnetic powder according to the first embodiment is a magnetic powder for a tape-shaped magnetic recording medium and contains magnetic particles (hereinafter sometimes referred to as "hexagonal ferrite particles") that have hexagonal ferrite as the main phase. In this specification, magnetic powder containing hexagonal ferrite particles may be referred to as hexagonal ferrite magnetic powder. Also, magnetic powder containing barium ferrite particles may be referred to as barium ferrite magnetic powder. 【0016】 In this technology, "magnetic powder" refers to an aggregate of multiple magnetic particles. This aggregate of multiple magnetic particles includes not only a configuration in which the multiple magnetic particles constituting the aggregate are in direct contact with each other, but also a configuration in which a binder, lubricant, or additive is interposed between the multiple magnetic particles. 【0017】 Hexagonal ferrite particles have a plate-like shape, such as a hexagonal plate, or a columnar shape, such as a hexagonal prism (provided that the thickness or height is smaller than the major axis of the plate surface or base surface). In this technology, "hexagonal plate-like shape" includes a substantially hexagonal plate-like shape. Similarly, "hexagonal prism-like shape" includes a substantially hexagonal prism-like shape. 【0018】 The hexagonal ferrite particles contain Fe and a metal M1 other than Fe. Metal M1 includes Ba and Sr selected from alkaline earth metals. It may also further contain Ca selected from alkaline earth metals. Metal M1 may also contain Pb in addition to alkaline earth metals. 【0019】 The hexagonal ferrite particles further contain metal M2 in addition to Fe and metal M1. Metal M2 can substitute for some of the Fe sites in the crystal structure of the hexagonal ferrite. Metal M2 contains Nd selected from rare earth elements. Metal M2 may further contain at least one other rare earth element selected from the group consisting of Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Furthermore, metal M2 may also contain, for example, at least one other transition metal element selected from the group consisting of metal elements of group 13 of the periodic table. 【0020】 In this technology, rare earth elements refer to Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Transition metal elements other than Fe refer to Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Hf, Ta, and W. Metal elements of Group 13 of the periodic table refer to Al, Ga, In, and Tl. 【0021】 In other words, the magnetic powder of this technology contains hexagonal ferrite particles comprising Fe, Ba, Sr, and Nd. Furthermore, the magnetic powder may further preferably contain at least one selected from the group consisting of Ti, Mn, Zr, and Sn. 【0022】Hexagonal ferrite particles may specifically refer to barium ferrite particles or strontium ferrite particles. In this technology, strontium ferrite particles refer to hexagonal ferrite particles in which the average atomic ratio of Sr to metal M1 (Sr / M1) is 50 atomic percent or more. Therefore, hexagonal ferrite particles containing Sr and metal M1 other than Sr are included in strontium ferrite particles if the average atomic ratio of Sr to metal M1 (Sr / M1) is 50 atomic percent or more. When metal M1 contains Sr and Ba, hexagonal ferrite particles in which the average atomic ratio of Sr to the total amount of Sr and Ba (Sr / (Sr+Ba)) is 50 atomic percent or more are called strontium ferrite particles. 【0023】 In this technology, barium ferrite particles refer to hexagonal ferrite particles in which the average atomic ratio of Ba to metal M1 (Ba / M1) is 50 atomic percent or more. Therefore, hexagonal ferrite particles containing Ba and metal M1 other than Ba ​​are included in barium ferrite particles if the average atomic ratio of Ba to metal M1 (Ba / M1) is 50 atomic percent or more. For example, if metal M1 contains Sr and Ba, hexagonal ferrite particles in which the average atomic ratio of Ba to the total amount of Sr and Ba (Ba / (Sr+Ba)) is 50 atomic percent or more are called barium ferrite particles. 【0024】 The atomic ratios of each element in magnetic powder are calculated from the analytical values ​​obtained by inductively coupled plasma atomic emission spectroscopy (ICP-AES) as follows. First, 0.1 g of the sample is wet-decomposed using acid, and then the solution is made up to 100 ml and quantitatively analyzed using ICP-AES as the sample solution. A blank sample is prepared by performing the same procedure with water. Next, the ratio of each element is calculated using the Fe concentration obtained from this measurement as 100%. If the hexagonal ferrite contains Sr and Ba, the atomic ratio of Sr to the total amount of Sr and Ba [atomic %] and the atomic ratio of Ba to the total amount of Sr and Ba [atomic %] are calculated using these results. 【0025】 (The atomic ratio of Nd to Fe (Nd / Fe)) 【0026】In the magnetic powder of this technology, the lower limit of the atomic ratio of Nd to Fe (Nd / Fe) is 0.0002 or higher, preferably 0.0010 or higher, more preferably 0.0015 or higher, even more preferably 0.0020 or higher, and even more preferably 0.0025 or higher. When the lower limit of the atomic ratio of Nd (Nd / Fe) is 0.0002 or higher, the plate-like ratio of the magnetic powder can be controlled, improving the magnetic anisotropy energy and enhancing the thermal stability of the magnetic recording medium. Furthermore, the upper limit of the atomic ratio of Nd to Fe (Nd / Fe) in the magnetic powder is 0.0050 or lower, preferably 0.0047 or lower, more preferably 0.0045 or lower, even more preferably 0.0044 or lower, and even more preferably 0.0043 or lower. If the upper limit of the atomic ratio of Nd to Fe (Nd / Fe) is 0.0050 or less, the generation of impurities that do not have the hexagonal ferrite crystal structure can be suppressed. Furthermore, the atomic ratio of Nd to Fe (Nd / Fe) in the magnetic powder is 0.0002 or more and 0.0050 or less, preferably 0.0010 or more and 0.0047 or less, more preferably 0.0015 or more and 0.0045 or less, even more preferably 0.0020 or more and 0.0044 or less, and even more preferably 0.0025 or more and 0.0043 or less. 【0027】 (The atomic ratio of Sr to Ba (Sr / Ba)) 【0028】Furthermore, the lower limit of the atomic ratio of Sr to Ba (Sr / Ba) in the magnetic powder is 0.6 or higher, preferably 0.62 or higher, more preferably 0.65 or higher, even more preferably 0.67 or higher, and even more preferably 0.7 or higher. When the lower limit of the atomic ratio of Sr (Sr / Ba) is 0.6 or higher, good magnetic properties can be obtained. Furthermore, the upper limit of the atomic ratio of Sr to Ba (Sr / Ba) in the magnetic powder is 1.0 or lower, preferably 0.99 or lower, more preferably 0.98 or lower, even more preferably 0.97 or lower, and even more preferably 0.96 or lower. When the upper limit of the atomic ratio of Sr to Ba (Sr / Ba) in the magnetic powder is 1.0 or lower, proper particle formation of the magnetic powder becomes easier. Furthermore, the atomic ratio of Sr to Ba (Sr / Ba) in the magnetic powder is 0.6 or more and 1 or less, preferably 0.62 or more and 0.99 or less, more preferably 0.65 or more and 0.98 or less, even more preferably 0.67 or more and 0.97 or less, and even more preferably 0.7 or more and 0.96 or less. 【0029】 The atomic ratio of Nd to Fe (Nd / Fe) and the atomic ratio of Sr to Ba (Sr / Ba) in the magnetic powder are calculated as follows. First, the magnetic powder sample is placed on carbon tape attached to the sample stage and pressed down. Excess magnetic powder that has not adhered is removed with an air blower to prepare the sample for analysis. The sample for analysis is observed using an ultra-high resolution field emission scanning electron microscope (FE-SEM SU-8600, Hitachi High-Tech Corporation) at an acceleration voltage of 15 kV and a magnification of 5000x, and compositional analysis (EDX analysis) is performed using an EDX (energy dispersive X-ray spectroscopy) device (Oxford Instruments, X-Max) equipped on the ultra-high resolution field emission scanning electron microscope. The target elements are the five elements Ti, Fe, Sr, Ba, and Nd, and quantification is performed so that the atomic concentrations of these elements become 100%. The included analysis software, E-MAX ver. 3.2, was used for quantification. EDX analysis was performed by randomly measuring 10 locations, and the quantitative value was taken as the average of these values. From the quantitative values ​​obtained in this way, the atomic ratio of Nd to Fe (Nd / Fe) and the atomic ratio of Sr to Ba (Sr / Ba) were calculated. 【0030】 Hexagonal ferrite may more specifically have an average composition represented by the following general formula (A): Sr （１－ｘ） Ba ｘ Fe （１２－ｙ） Nd ｙ O １９ ... (A) (However, in equation (A), x represents 0.5 < x ≤ 1, preferably 0.5 < x < 1. y represents 0.5 ≤ y < 1.) 【0031】 (Average plate diameter) 【0032】 The lower limit of the average plate diameter of the magnetic powder is preferably 8.0 nm or more, more preferably 10.0 nm or more, even more preferably 12.0 nm or more, and even more preferably 13.0 nm or more. When the lower limit of the average plate diameter of the magnetic powder is 8.0 nm or more, thermal stability can be improved. The upper limit of the average plate diameter of the magnetic powder is preferably 20.0 nm or less, more preferably 18.0 nm or less, even more preferably 16.0 nm or less, and even more preferably 15.0 nm or less. When the upper limit of the average plate diameter of the magnetic powder is 20.0 nm or less, noise can be reduced, and a magnetic recording medium suitable for high-density recording can be obtained. The average plate diameter of the magnetic powder is preferably 8.0 nm or more and 20.0 nm or less, more preferably 10.0 nm or more and 20.0 nm or less, even more preferably 12.0 nm or more and 20.0 nm or less, and even more preferably 13.0 nm or more and 20.0 nm or less. 【0033】 (Average lamellar ratio) 【0034】 In the magnetic recording medium of this technology, the average plate thickness DA of the magnetic powder ａｖｅ The average plate diameter DB of the magnetic powder ａｖｅ The average plate ratio (DB) is the ratio of ａｖｅ / DA ａｖｅ The lower limit of the magnetic powder is preferably 1.0 or higher, more preferably 1.2 or higher, even more preferably 1.4 or higher, and even more preferably 1.6 or higher. ａｖｅ The average plate diameter DB of the magnetic powder ａｖｅ The average plate ratio (DB) is the ratio of ａｖｅ / DA ａｖｅThe upper limit of ) is preferably 3.0 or less, more preferably 2.9 or less, even more preferably 2.8 or less, and even more preferably 2.6 or less. Also, the plate ratio (DB ａｖｅ / DA ａｖｅ The plate ratio (DB) is preferably 1.0 to 3.0, more preferably 1.2 to 2.9, even more preferably 1.4 to 2.8, and even more preferably 1.6 to 2.6. ａｖｅ / DA ａｖｅ If the coefficient of gravity is within the range of 1.0 to 3.0, aggregation of hexagonal ferrite particles contained in the magnetic powder can be suppressed. Furthermore, the resistance applied to the hexagonal ferrite particles when they are vertically oriented during the magnetic layer formation process can be suppressed. Therefore, the vertical orientation of the hexagonal ferrite particles can be improved. 【0035】 Average plate diameter DB of magnetic powder ａｖｅ and average lamellar ratio (DB ａｖｅ / DA ａｖｅ The following is how it is determined. First, the magnetic tape MT housed in the cartridge 10 shown in Figure 18 is unwound, and the magnetic tape MT is cut out at a position 30 m in the longitudinal direction from the connection part 21 between the magnetic tape MT and the leader tape LT. Next, the magnetic tape MT to be measured is processed and thinned using the FIB method or the like. When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment before observing the TEM image of the cross-section described later. The carbon layer is formed on the surface of the magnetic layer 43 side and the back layer 44 side of the magnetic tape MT by vapor deposition, and the tungsten layer is further formed on the surface of the magnetic layer 43 side by vapor deposition or sputtering. This thinning is performed along the length direction (longitudinal direction) of the magnetic tape MT. That is, this thinning creates a cross-section parallel to both the longitudinal direction and the thickness direction of the magnetic tape MT. 【0036】The cross-section of the obtained thin section sample is observed using a transmission electron microscope (Hitachi High-Technologies Corporation H-9500) with an acceleration voltage of 200 kV and a total magnification of 500,000x, ensuring that the entire magnetic layer 43 is included in the thickness direction of the magnetic layer 43, and a TEM image is taken. The TEM images are prepared in a number that allows for the extraction of 50 particles capable of measuring the plate diameter DB and plate thickness DA (see Figure 1) shown below. 【0037】 In this specification, if the shape of the particles observed in the above TEM photograph is plate-like or columnar (however, the thickness or height is smaller than the major axis of the plate surface or base surface), as shown in Figure 1, the maximum long side distance of the particles observed in the above TEM photograph shall be the value of the plate diameter DB. The thickness or height of the particles observed in the above TEM photograph shall be the value of the plate thickness DA. If the thickness or height of particles is not constant within a single particle, the thickness or height of the largest particle shall be the plate thickness DA. 【0038】 Next, 50 particles are selected from the captured TEM images based on the following criteria: Particles whose portion extends outside the field of view of the TEM image are not measured; only particles with clear outlines and existing in isolation are measured. If there is overlap between particles, those with clear boundaries and whose overall shape can be determined are measured as individual particles; however, particles with unclear boundaries and whose overall shape cannot be determined are not measured as their shape cannot be determined. 【0039】 Figures 2 and 3 show examples of TEM images. In Figures 2 and 3, for example, the particles indicated by arrows a and d are selected because their particle thickness (thickness or height) DA can be clearly confirmed. The particle thickness DA of each of the 50 selected particles is measured. The particle thickness DA obtained in this way is simply averaged (arithmetic mean) to obtain the average particle thickness DA. ａｖｅ We will find the average plate thickness DA. ａｖｅThis is the average particle thickness. Next, the diameter DB of each magnetic powder is measured. To measure the particle diameter DB, 50 particles whose diameter DB can be clearly identified are selected from the TEM images taken. For example, in Figures 2 and 3, the particles indicated by arrows b and c are selected because their diameter DB can be clearly identified. The diameter DB of each of the 50 selected particles is measured. The average diameter DB obtained in this way is calculated by taking a simple average (arithmetic mean) of the resulting diameter DB. ａｖｅ We will find the average plate diameter DB. ａｖｅ However, this is the average particle size. And the average plate thickness DA ａｖｅ and average plate diameter DB ａｖｅ From the average plate ratio of the particles (DB ａｖｅ / DA ａｖｅ ) 【0040】 (Average particle volume) 【0041】 The upper limit of the average particle volume of the magnetic powder is preferably 1600 nm. ３ More preferably, 1500 nm ３ More preferably 1400 nm ３ More preferably, 1300 nm ３ The following applies: The upper limit of the average particle volume of magnetic powder is 1600 nm. ３ When the following conditions are met, a sufficient number of magnetic particles can be included per unit area when a magnetic tape is manufactured using magnetic powder, thereby improving the electromagnetic conversion characteristics of the magnetic tape. Furthermore, the lower limit of the average particle volume is preferably 400 nm. ３ The above describes a more comfortable 500 nm ３ More preferably 600 nm ３ That's all. The lower limit of the average particle volume of magnetic powder is 200 nm. ３ As described above, when a magnetic tape is manufactured using magnetic powder, degradation of the playback signal due to thermal fluctuations can be suppressed. Therefore, the electromagnetic conversion characteristics of the magnetic tape can be improved. Furthermore, the average particle volume of the magnetic powder is preferably 1600 nm. ３ 200nm or less ３ More preferably, 1500 nm ３ Below 300nm ３More preferably 1400 nm ３ Below 400nm ３ More preferably, 1300 nm ３ Below 500nm ３ That's all. 【0042】 The average particle volume of the magnetic powder can be determined as follows. First, the average plate diameter DB of the magnetic powder is ａｖｅ and average lamellar ratio (DB ａｖｅ / DA ａｖｅ As described regarding the calculation method of the average plate thickness DA ａｖｅ and average plate diameter DB ａｖｅ Next, we calculate the average particle volume V of the magnetic powder using the following formula. 【0043】 【0044】 Furthermore, the particle volume of magnetic powder can also be determined using the measurement results obtained by XRD (X-ray Diffraction). The particle volume of magnetic powder determined by XRD is called the XRD volume. The XRD volume is determined as follows: First, magnetic powder is placed in a recess (square, 1.8 cm x 2.0 cm) of an XRD non-reflective silicon sample plate, and the sample is prepared by leveling it with a glass plate. Next, the X-ray diffraction pattern of the sample is measured using the concentration method. 【0045】 For example, the composition formula BaFe １２ O １９ For hexagonal ferrite represented by , the crystallite size D is obtained from the diffraction peaks of the (0,0,6) plane. １ The crystallite size D is calculated, and for hexagonal ferrite containing Sr, the crystallite size obtained from the diffraction peaks of the (1,1,4) plane is multiplied by a correction factor of 0.5406. １ The crystallite size D is calculated here. １ This value corresponds to the thickness of the particle. In this specification, crystallite size D １ plate thickness D １ That happens. 【0046】Note that since the intensity of the (0, 0, 6) plane of the hexagonal ferrite containing Sr appears weak, the crystallite size D is obtained by multiplying the (1, 1, 4) plane, where the intensity appears relatively high, by a correction factor. １ is calculated. Also, the crystallite size D ２ is calculated from the diffraction peak of the (2, 2, 0) plane. Here, the crystallite size D ２ is a value corresponding to the particle size (plate diameter) of the particles. In this specification, the crystallite size D ２ is sometimes referred to as the particle size D ２ or the plate diameter D ２ . The crystallite size D １ and the crystallite size D ２ are calculated using the following Scherrer's formula. Scherrer's formula: Dx = Kλ / Bcosθ Dx: crystallite size (nm) λ: wavelength of the measured X-ray (nm) B: broadening of the diffraction line due to the crystallite size (half-value width of the diffraction peak) θ: angle at which the diffraction peak appears K: Scherrer constant (= 0.94) 【0047】 The measurement conditions for X-ray diffraction are as follows. Equipment used: XRD (Ultima IV, manufactured by Rigaku) Measurement mode: focused normal line source: Co (CoKα ray, wavelength λ = 0.179 nm) Voltage: 40 kV Current: 40 mA Divergence slit: 1 / 2° Divergence vertical limiting slit: 5 mm Scattering slit: 8 mm Receiving slit: open Step width: 0.02° Scan speed: 1° / min Scanning range: 20° to 80° Analysis software: PDXL2 【0048】 Next, the XRD volume (crystallite volume) V ＸＲＤ of the magnetic powder is obtained 【0049】 【0050】 However, D １ is the crystallite size calculated from the diffraction peak of the (0, 0, 6) plane in the case of the hexagonal ferrite represented by the composition formula BaFe １２ O １９ , and in the case of the hexagonal ferrite containing Sr, it is the value obtained by multiplying the crystallite size obtained from the diffraction peak of the (1, 1, 4) plane by the correction factor 0.5406. D２ is the crystallite size calculated from the diffraction peak of the (2, 2, 0) plane. 【0051】 In a magnetic powder and a magnetic recording medium using the powder, when a plurality of XRD volumes measured with the magnetic powder and TEM volumes obtained from TEM photographs of the magnetic recording medium using the powder are plotted, a strong correlation can be confirmed. For the XRD volume (x), the TEM volume (y) is calculated by the following equation. y = 1.54x - 800 【0052】 (Crystal magnetic anisotropy constant K ｕ ) 【0053】 The lower limit of the crystal magnetic anisotropy constant K of the magnetic powder of the present technology ｕ is preferably 2.20 × 10 ６ erg / cc or more, more preferably 2.25 × 10 ６ erg / cc or more, still more preferably 2.30 × 10 ６ erg / cc or more, even more preferably 2.35 × 10 ６ erg / cc or more. When the lower limit of the crystal magnetic anisotropy constant K of the magnetic powder is ｕ 2.20 × 10 ６ erg / cc or more, the necessary thermal stability can be ensured. Also, the upper limit of the crystal magnetic anisotropy constant K of the magnetic powder ｕ is preferably 2.70 × 10 ６ erg / cc or less, more preferably 2.65 × 10 ６ erg / cc or less, still more preferably 2.60 × 10 ６ erg / cc or less, even more preferably 2.55 × 10 ６ erg / cc or less. When the upper limit of the crystal magnetic anisotropy constant K of the magnetic powder is ｕ 2.70 × 10 ６ erg / cc or less, the writing performance of the magnetic head can be ensured. Also, the crystal magnetic anisotropy constant K of the magnetic recording medium ｕ is preferably 2.20 × 10 ６ erg / cc or more and 2.70 × 10 ６ erg / cc or less, more preferably 2.25 × 10 ６ erg / cc or more and 2.65 × 10 ６erg / cc or less, more preferably 2.30 × 10 ６ erg / cc or more 2.60×10 ６ erg / cc or less, more preferably 2.35 × 10 ６ erg / cc or more 2.55×10 ６ It is less than or equal to erg / cc. 【0054】 Crystal magnetic anisotropy constant K of magnetic powder ｕ The following is how it is obtained: (i) First, the magnetic tape MT housed in the cartridge 10 shown in Figure 18 is unwound, and three pieces of the magnetic tape MT are cut to a predetermined size at a position 30 m in the longitudinal direction from the connection part 21 between the magnetic tape MT and the leader tape LT. These three pieces are then stacked and glued together, and both sides are glued with mending tape to obtain a laminate. Then, a circular sample is obtained by punching a hole in the obtained laminate with a round punch with a diameter of φ = 6.25. (ii) Next, the obtained sample is AC demagnetized. This process is performed considering that if a magnetized sample is used, the magnetization may saturate when an external magnetic field is applied, and the torque output value may not be normal. (iii) Next, the sample is set in the measuring device. Specifically, if the magnetic powder is vertically oriented, the sample is set perpendicular to the direction of the applied magnetic field. On the other hand, if the magnetic powder is longitudinally oriented, the sample is set horizontally to the direction of the applied magnetic field. (iv) Next, after adjusting the measuring device (TRT-2 type, manufactured by Toei Kogyo Co., Ltd.) to zero magnetic field, an external magnetic field of 15000 [Oe] is applied in torque angle measurement mode and the torque waveform is measured. (v) First, thermal stability (K ｕ V ａｃｔ / k Ｂ T, K ｕ : The crystalline magnetic anisotropy constant of magnetic powder, V ａｃｔ : Activation volume of magnetic powder, k ＢThe Boltzmann constant (T: absolute temperature) is calculated using Sherrock's formula shown below (Reference: IEEE TRANSACTIONS ON MAGNETICS, VOL. 50, NO. 11, NOVEMBER 2014, J. Flanders and MP Sharrock: J. Appl. Phys., 62, 2918 (1987)). ｒ (t') = H ０ [1-{k Ｂ T / (K ｕ V ａｃｔ ) ln (f ０ t' / 0.693)} ｎ ] (However, H ｒ : residual magnetic field, t': magnetization attenuation, H ０ : Magnetic field change, k Ｂ : Boltzmann constant, T: absolute temperature, K ｕ : Crystal magnetic anisotropy constant, V ａｃｔ : Activation volume, f ０ : frequency factor, n: coefficient) 【0055】 Note that (a) residual magnetic field H ｒ (b) magnetization decay t' and (c) magnetic field change H ０ The following can be obtained. Also, (d) frequency factor f ０ (e) The coefficient n is the following value: (a) Residual magnetic field H ｒ (b) The magnetization attenuation t' is determined as follows: the coercivity H of the magnetic recording medium. ｃ An external magnetic field is applied in the vicinity of the object under three conditions, and the magnetization decay is measured using a VSM. Then, the magnetization decay t' is calculated from this magnetization decay using Flanders' equation described in the above reference. Here, "coercivity H ｃ " is the coercivity H in the orientation direction of magnetic powder. ｃ This means that when magnetic powder is oriented vertically, the coercivity is H ｃ " refers to the coercive force H in the vertical direction. ｃ This means that when the magnetic powder is oriented in the longitudinal direction, the coercivity H ｃ " is the coercive force H in the longitudinal direction.ｃ This means that the "external magnetic field with three conditions" refers to the coercivity H ｃ The above magnetic field (a magnetic field that yields positive magnetization), coercivity H ｃ The nearby magnetic field (a magnetic field that yields magnetization close to zero), and the coercivity H ｃ This refers to a magnetic field less than 100 (a magnetic field that produces negative magnetization). (c) Magnetic field change H ０ This is a constant that appears when calculating the magnetization decay t'. (d) Frequency factor f ０ = 5.0 × 10 ９ Let the unit be Hz. (e) The coefficient n is set to a value corresponding to the crystalline magnetic anisotropy of the cobalt ferrite particles. If the cobalt ferrite particles have uniaxial crystalline magnetic anisotropy and are oriented in the vertical direction, n is set to 0.5. On the other hand, if the cobalt ferrite particles are unoriented, n is set to 0.77. 【0056】 As described above, the thermal stability (K) can be calculated using Sherlock's formula. ｕ V ａｃｔ / k Ｂ T, K ｕ : The crystalline magnetic anisotropy constant of magnetic powder, V ａｃｔ : Activation volume of magnetic powder, k Ｂ The Boltzmann constant (where T is the absolute temperature) is calculated. Next, in torque angle measurement mode, external magnetic fields of 10000, 12500, and 15000 Oe are applied as the applied magnetic field, and the crystal magnetic anisotropy constant K is calculated using the saturation extrapolation method. ｕ The crystal magnetic anisotropy constant K is calculated. ｕ In the case of vertical orientation, K ｕ 1 and K ｕ It is calculated as the sum of 2, and in the case of longitudinal orientation, K ｕ The calculation is performed using only 1. Then, the calculated crystal magnetic anisotropy constant K is calculated. ｕ Substituting the absolute temperature T = 300 K (room temperature) into Sherlock's equation, we get the activation volume V. ａｃｔ We seek. 【0057】 (Thermal stability (K ｕ V ａｃｔ / k Ｂ T, K ｕ )) 【0058】 Thermal stability of magnetic powder (K ｕ Vａｃｔ / k Ｂ T, K ｕ : The crystalline magnetic anisotropy constant of magnetic powder, V ａｃｔ : Activation volume of magnetic powder, k Ｂ The thermal stability (where ∫ is the Boltzmann constant and T is the absolute temperature) is preferably 60 or higher, more preferably 80 or higher, and even more preferably 85 or higher. When the thermal stability is 60 or higher, the decrease in thermal stability can be suppressed when a magnetic tape is manufactured using magnetic powder. Therefore, the degradation of the output signal of the magnetic tape can be suppressed. 【0059】 (SFD) 【0060】 The lower limit of the Switching Field Distribution (SFD) of the magnetic powder is preferably 0.1 or higher, more preferably 0.2 or higher, even more preferably 0.3 or higher, and even more preferably 0.5 or higher. The upper limit of the Switching Field Distribution (SFD) of the magnetic powder is preferably 1.5 or lower, more preferably 1.4 or lower, even more preferably 1.3 or lower, and even more preferably 1.2 or lower. The Switching Field Distribution (SFD) of the magnetic powder is preferably 0.1 to 1.5, more preferably 0.2 to 1.4, even more preferably 0.3 to 1.3, and even more preferably 0.5 to 1.0. 【0061】The Switching Field Distribution (SFD) of magnetic powder is determined as follows. First, a magnetic powder sample is prepared by packing magnetic powder into a resin capsule with an inner diameter of 6 mm and a depth of 2.5 mm, and then closing the lid. At this time, care is taken to ensure that the magnetic powder is sufficiently fixed inside the capsule. Next, the M-H loop of the magnetic powder sample is measured using a Vibrating Sample Magnetometer (VSM, VSM-P7-15 model, manufactured by Toei Kogyo Co., Ltd.). The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 12 bits, time constant of Locking amp: 0.03 sec, waiting time: 0.1 sec, MH average number: 20. After obtaining the M-H loop of the magnetic powder sample, the coercivity H was determined from the obtained M-H loop. ｃ We will find the coercivity H. ｃ The calculation of this value is performed using the measurement and analysis program included with the "VSM-P7-15" model. The M-H loop measurement described above should be performed at room temperature (25°C). 【0062】 Coercive force H ｃ In the same manner as the measurement, the SFD curve (differential curve of the M-H loop) is obtained from the M-H loop. In the SFD curve of the magnetic powder, the full width at half maximum (FMAX) of the main peak is H ａ The coercivity of magnetic powder is H ｃ In that case, SFD is H ａ / H ｃ This is calculated using the SFD curve and the full width at half maximum (H). ａ The measurement and analysis program included with the "VSM-P7-15" is used for the calculation. 【0063】 (Coercive force H ｃ ) 【0064】 The aforementioned magnetic powder is H ｃ The lower limit of the coercivity is preferably 2200 Oe or more, more preferably 2250 Oe or more, even more preferably 2300 Oe or more, and even more preferably 2350 Oe or more. ｃIf the lower limit of the coercivity is 2200 Oe or higher, it is possible to suppress the loss of written data due to thermal fluctuations when magnetic tape is manufactured using magnetic powder. Furthermore, the magnetic powder is H ｃ The upper limit of the coercivity is preferably 2700 Oe or less, more preferably 2650 Oe or less, even more preferably 2600 Oe or less, and even more preferably 2550 Oe or less. ｃ If the upper limit of the coercivity is 2700 Oe or less, saturation recording by the recording head becomes easier, and sufficient electromagnetic conversion characteristics can be achieved even at high recording densities. Furthermore, the magnetic powder is H ｃ The coercivity is preferably 2200 Oe or more and 2700 Oe or less, more preferably 2250 Oe or more and 2650 Oe or less, even more preferably 2300 Oe or more and 2600 Oe or less, and even more preferably 2350 Oe or more and 2550 Oe or less. ｃ The method for measuring coercivity is as described above. 【0065】 (Half-Maximum Width H) ａ ) 【0066】 The aforementioned magnetic powder is H ａ The upper limit of the (full width at half maximum) is preferably 4000 Oe or less, more preferably 3900 Oe or less, even more preferably 3800 Oe or less, and even more preferably 3700 Oe or less. ａ If the upper limit of the (half-width) is 4000 Oe or less, noise in the magnetic tape can be suppressed. ａ The method for measuring the (full width at half maximum) is as described above. 【0067】 (Saturation magnetization σs) 【0068】 The lower limit of the saturation magnetization σs of the magnetic powder is preferably 49.5 emu / g or higher, more preferably 50.0 emu / g or higher, and even more preferably 50.5 emu / g or higher. When the saturation magnetization σs is 49.5 emu / g or higher, high output can be obtained even with a thin magnetic layer, thus enabling good electromagnetic conversion characteristics. 【0069】The upper limit of the saturation magnetization σs of the magnetic powder is preferably 54.0 emu / g or less, more preferably 53.5 emu / g or less, and even more preferably 53.0 emu / g or less. If the saturation magnetization σs exceeds 54.0 emu / g, the GMR (Giant Magnetoresistive), TMR (Tunneling Magnetoresistive) heads, etc., that read the magnetization signal will become saturated, which may lead to a decrease in electromagnetic conversion characteristics. 【0070】 The saturation magnetization σs mentioned above can be determined as follows: that is, the coercivity H of the magnetic powder mentioned above. ｃ In the same manner as the measurement method described above, an M-H loop is obtained from the magnetic powder sample, and then the saturation magnetization σs is determined from the obtained M-H loop. 【0071】 (2) Method for producing magnetic powder 【0072】 Hereinafter, with reference to Figure 4, an example of a method for producing magnetic powder according to the first embodiment of this disclosure will be described. This method for producing magnetic powder uses a so-called glass crystallization method. 【0073】 (Raw material mixing process) 【0074】 First, in step S1, the hexagonal ferrite-forming component (magnetic powder raw material) and the glass-forming component (glass raw material) are mixed. For example, the magnetic material containing the hexagonal ferrite-forming component and the glass-forming component is placed in a container made of plastic or the like, and then mixed in a powder mixer for a predetermined time (for example, 60 minutes). 【0075】 Glass-forming components are glass raw materials that exhibit a glass transition phenomenon and can become amorphous, i.e., glass raw materials that can be vitrified. Examples of glass-forming components include sodium tetraborate (Na ２ B ４ O ７ ) and boric acid oxide (B ２ O ３ ) includes at least one of the following. 【0076】 The hexagonal ferrite-forming component is a compound containing atoms that constitute the crystalline structure of hexagonal ferrite, and includes, for example, metal carbonates and iron oxides. The metal carbonate is at least strontium carbonate (SrCO3).３ ) contains. Metal carbonates further include barium carbonate (BaCO3). ３ ) may further contain. Iron oxide may be, for example, ferric oxide (Fe ２ O ３ ) contains SrCO in the hexagonal ferrite forming component. ３ The content of is preferably higher than the content of iron oxide in the hexagonal ferrite-forming component. 【0077】 The content of each component in the raw material mixture is determined according to the composition of the hexagonal ferrite particles to be obtained. For example, the content of the glass-forming component in the raw material mixture is 30 mol% or less. The raw material mixture can be prepared by weighing the various components and then mixing them. 【0078】 During the above mixing process, an oxide of metal M2 may be further added as needed. The oxide of metal M2 may be, for example, titanium oxide (TiO2). ２ ), aluminum oxide (Al ２ O ３ ) and neodymium oxide (Nd ２ O ３ It includes at least one species selected from the group consisting of the following: 【0079】 (melting process) 【0080】 Next, in step S2, the raw material mixture is dissolved to obtain a solution. The raw material mixture can be dissolved, for example, in a glass melting furnace. For example, the raw material mixture is placed in the crucible of a glass melting furnace and dissolved at a melting temperature of, for example, 1300°C to 1500°C. The dissolution time should be set appropriately so that the raw material mixture is sufficiently melted. For example, if 1 kg of raw material mixture is placed in a glass melting furnace, the dissolution time can be, for example, 80 minutes. It is also preferable to dissolve the raw material mixture in the melting furnace while stirring it with a stirring device. This is to reduce temperature unevenness in the melting furnace and promote the amorphous formation of the solution obtained by dissolving the raw material mixture. When the content of glass raw materials in the raw material mixture is low, for example to 30 mol% or less, relatively iron oxide (Fe ２ O ３The content of components containing ) increases. In that case, the melting point of the raw material mixture rises, so stirring is important to homogenize the temperature distribution in the furnace and eliminate uneven dissolution. Stirring also prevents the dissolved material from clogging the discharge port when the dissolved material is discharged from the melting furnace. The stirring device should be set to stir at a rotational speed of, for example, 30 rpm or more. 【0081】 (Rapid cooling process) 【0082】Next, in step S3, the dissolved raw material mixture is rapidly cooled to generate an amorphous mass containing crystal nuclei. This rapid cooling can be carried out in the same way as the rapid cooling process normally performed to obtain an amorphous mass in the glass crystallization method. For example, a method of rapidly cooling the dissolved material while rolling it using a pair of rapidly rotating cooling rolls is preferred. The pair of cooling rolls should, for example, have cooling water circulating through internal channels to maintain a constant surface temperature. This is to stabilize the rapid cooling efficiency and promote the amorphousization of the dissolved material. The surface temperature of the cooling rolls is set to, for example, 20°C. The distance between the pair of cooling rolls is set to, for example, 1 mm or less, and the discharge rate is set to, for example, 0.5 g / second or more and 1.0 g / second or less. Note that "rapid cooling" means rapidly cooling the dissolved raw material mixture to near room temperature and putting the dissolved material into a disordered state (hereinafter referred to as the amorphous state). One condition for putting the material into an amorphous state is that the cooling rate exceeds the crystal growth rate. Putting the material into an amorphous state makes it possible to control the growth of nanoparticles and the particle size of nanoparticles. If the cooling rate is slower than the crystal growth rate, crystal growth of the particles will occur before they transition to the amorphous state, resulting in a mixture of amorphous and crystalline states in the solution. Therefore, if rapid cooling is not successful and the raw material mixture does not sufficiently become amorphous, amorphous and crystalline states will coexist in the solution. Consequently, in the subsequent firing process, particles that grow from the amorphous state and particles that grow from a crystalline state of a certain size will be mixed in the magnetic powder (hexagonal ferrite magnetic powder). Therefore, it is thought that variations will occur in the particle size distribution and magnetic properties of the resulting magnetic powder (hexagonal ferrite magnetic powder). 【0083】 (Grinding process) 【0084】Next, in step S4, the amorphous mass is crushed using, for example, a pulverizer to obtain amorphous powder containing crystal nuclei. Here, amorphous powder containing crystal nuclei refers to an aggregate of amorphous particles containing crystal nuclei. As the pulverizer, for example, a roller mill, jet mill, high-speed rotary pulverizer, container-driven mill, etc. can be used, but the pulverizer is not limited to these in particular. 【0085】 (Classification process) 【0086】 Next, in step S5, the amorphous powder is subjected to a classification process. The classification process may be repeated multiple times as needed. By the classification process, the amorphous powder is divided into multiple groups according to the range of particle size, and it is preferable that the amorphous powder of the group with the smallest particle size range is removed. The hexagonal ferrite powder obtained by calcining the amorphous powder of the group with the smallest particle size range is a hexagonal ferrite particle with low magnetic properties (e.g., coercivity H ｃ This is because it is highly likely to contain a large amount of hexagonal ferrite particles (which have a near-zero molecular weight). 【0087】 The amorphous powder removed by classification preferably contains amorphous particles with a particle size of 300 μm or less. The hexagonal ferrite powder obtained by calcining the amorphous powder with a particle size of 300 μm or less preferably contains hexagonal ferrite particles having particularly low magnetic properties (e.g., coercivity H ｃ This is because it is highly likely to contain a large amount of hexagonal ferrite particles (which have a near-zero ferrous oxide content). For example, when sieving is used for classification, it can be confirmed by the size of the sieve opening that amorphous particles with a particle size of 300 μm or less have been removed by the classification. 【0088】Classification can be performed using either wet or dry methods, with dry classification being preferred. This is because when wet classification is used, there is a risk that amorphous powder may dissolve when the classification process is carried out in a liquid such as water. For dry classification, sieving or air classification can be used, and both may be used in combination. For air classification, gravity classification, inertial classification, or centrifugal classification can be used, and two or more of these classifications may be used in combination. 【0089】 When sieving is used for classification, the mesh size of the sieve used is preferably 300 μm or less. This allows amorphous powder particles with a particle size of 300 μm or less to be removed by classification. Here, the mesh size of the sieve is the mesh size specified in JIS Z 8801-1:2019. 【0090】 (Firing process) 【0091】 Next, in step S6, after the amorphous powder is placed in the crucible, the crucible is placed in a predetermined position in the electric furnace. The crucible is an example of a firing container. Examples of materials for the crucible include ceramics such as alumina (aluminum oxide), magnesia (magnesium oxide), zirconia (zirconium oxide), SiC (silicon carbide), or AlN (aluminum nitride). From the viewpoint of improving the thermal conductivity of the crucible, SiC (silicon carbide) or AlN (aluminum nitride) are preferred among these materials. 【0092】Next, the furnace is heated from room temperature to a predetermined temperature, and after reaching the predetermined temperature, the furnace is maintained at that temperature for a predetermined time to calcine the amorphous powder and obtain a calcined body. During this process, crystals grow from crystal nuclei within the amorphous particles. That is, hexagonal ferrite particles are precipitated within the amorphous particles. The particle size of the precipitated hexagonal ferrite particles can be controlled by the calcination conditions. Raising the calcination temperature for crystallization (crystallization temperature) may lead to an increase in the particle size of the precipitated hexagonal ferrite particles. Therefore, it is preferable that the temperature be as low as possible, but above the temperature at which crystallization of hexagonal ferrite occurs. Specifically, it is preferable to generate crystals by calcining the amorphous powder at a calcination temperature of 570°C to 630°C. The calcination time for crystallization (holding time at the above crystallization temperature) is, for example, 1 hour to 48 hours, and it is desirable to perform it for, for example, 8 hours or more. Furthermore, the heating rate until the firing temperature is reached is, for example, 1.0°C / min or more and 10.0°C / min or less, specifically, for example, 5.0°C / min or less. The firing process may be carried out in one or two stages, or in three or more stages. 【0093】 (Acid treatment and washing process) 【0094】 Next, in step S7, the calcined body is subjected to acid treatment. This dissolves the glass components surrounding the hexagonal ferrite particles, and the hexagonal ferrite particle powder is extracted. The acid treatment may be carried out, for example, by immersing the calcined body in an acid such as acetic acid and washing it with a ball mill. Next, the extracted hexagonal ferrite particle powder is washed with pure water. 【0095】 (Separation process) 【0096】 Next, in step S8, the boric acid glass and hexagonal ferrite particles dissolved in water by the acid treatment are separated (decanted) using a centrifuge. This removes impurities such as glass components. 【0097】 (drying process) 【0098】Next, in step S9, the hexagonal ferrite particle powder from which the glass component has been removed is washed with water and then dried. It is preferable to crush the calcined body before the acid treatment in order to improve the efficiency of the acid treatment. The crushing treatment may be carried out by either a dry or wet method. This yields the desired magnetic powder. 【0099】 In the above method for producing magnetic powder, Na is used as a glass raw material. ２ B ４ O ７ , B ２ O ３ and H ３ BO ３ At least one of the following is used, and Na is used as a glass raw material in the raw material mixture. ２ B ４ O ７ , B ２ O ３ and H ３ BO ３ It is preferable that the content of at least one of the materials be 30 mol% or less. By keeping the content of glass raw materials in the raw material mixture low in this way, the number of nucleating particles that serve as nuclei for hexagonal ferrite particles in the raw material mixture increases relatively. Nucleating particles include, for example, SrCO3 as a magnetic material raw material. ３ Sr atoms and Fe contained ２ O ３ These are Fe atoms contained within. It is thought that a relative increase in the number of nucleated particles generates a large number of hexagonal ferrite particles, thereby suppressing the coarsening of individual hexagonal ferrite particles. 【0100】 Furthermore, in the above method for producing magnetic powder, the SrCO3 in the magnetic material raw material ３ The content (molar ratio) of Fe in magnetic material raw materials ２ O ３It is preferable that the content (molar ratio) of Sr be higher than that of Fe. That is, it is preferable that the content (molar ratio) of Sr be higher than that of Fe. This results in the generation of a large number of hexagonal ferrite particles. Therefore, it is thought that the coarsening of individual hexagonal ferrite particles is suppressed. Strontium has a high ionization tendency and dissolves in the glass to some extent. Therefore, if the content (molar ratio) of Sr is equal to or less than that of Fe, there will be a shortage of strontium, and the number of hexagonal ferrite particles generated will decrease. As a result, individual hexagonal ferrite particles tend to coarseen. 【0101】 3. Second Embodiment 【0102】 (1) Configuration of magnetic recording medium 【0103】 Next, a magnetic recording medium according to a second embodiment of this technology will be described with reference to the figures. Figure 5 is a cross-sectional view showing an example of the configuration of a magnetic tape MT according to a second embodiment of this technology. The magnetic tape MT comprises a long base body 41, a base layer 42 provided on one main surface (first main surface) of the base body 41, a magnetic layer 43 provided on the base layer 42, and a back layer 44 provided on the other main surface (second main surface) of the base body 41. The base layer 42 and the back layer 44 are provided as needed and may be omitted. The magnetic tape MT is preferably a vertical recording type magnetic recording medium. The magnetic tape MT preferably contains a lubricant from the viewpoint of improving runability. The lubricant may be contained in at least one of the base layer 42 and the magnetic layer 43. The magnetic tape MT may further include a lubricant layer provided on the surface of the magnetic layer 43 (hereinafter appropriately referred to as "magnetic surface"). The magnetic tape MT may be housed in a cartridge. 【0104】The magnetic tape MT may conform to the LTO standard or to a standard other than the LTO standard. The width of the magnetic tape MT may be 1 / 2 inch or wider than 1 / 2 inch. If the magnetic tape MT conforms to the LTO standard, the width of the magnetic tape MT is 1 / 2 inch. The magnetic tape MT may have a configuration that allows the width of the magnetic tape MT to be kept constant or nearly constant by adjusting the tension applied to the longitudinal direction of the magnetic tape MT during travel using a recording and playback device (drive). 【0105】 The magnetic tape MT has a long length and is run in the longitudinal direction during recording and playback. The magnetic tape MT is preferably used in a recording and playback device equipped with a ring-type head as the recording head. The magnetic tape MT is configured to record signals at a linear recording density D. From the viewpoint of increasing recording capacity, the lower limit of the linear recording density D of signals that can be recorded on the magnetic tape MT is preferably 545 kfci or more, more preferably 549 kfci or more, even more preferably 550 kfci or more, 552 kfci or more, 577 kfci or more, 600 kfci or more, or 635 kfci or more. The upper limit of the linear recording density D of data that can be recorded on the magnetic tape MT is preferably 1270 kfci or less, considering the size of the magnetic particles. 【0106】 The magnetic tape MT is preferably reproduced using a playback head that employs a TMR element. The signal reproduced by the playback head using the TMR may be data recorded in the data band DB (see Figure 6), or it may be a servo pattern (servo signal) recorded in the servo band SB (see Figure 6). 【0107】 (2) Explanation of each layer 【0108】 (Base) 【0109】The substrate 41 is a non-magnetic support that supports the underlayer 42 and the magnetic layer 43. The substrate 41 has a long film-like structure. The upper limit of the average thickness of the substrate 41 is preferably 4.40 μm or less, more preferably 4.20 μm or less, even more preferably 4.00 μm or less, 3.80 μm or less, or 3.40 μm or less, from the viewpoint of improving the recording capacity that can be recorded in one data cartridge. The lower limit of the average thickness of the substrate 41 is preferably 3.00 μm or more, more preferably 3.20 μm or more, even more preferably 3.80 μm or more, or 3.9 μm or more, from the viewpoint of suppressing a decrease in the strength of the substrate 41. The numerical range of the average thickness of the substrate 41 may be defined by either of the upper limits and either of the lower limits, and is preferably 3.80 μm or more and 4.40 μm or less, and more preferably 3.90 μm or more and 4.40 μm or less. 【0110】 The average thickness of the substrate 41 is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and a sample is prepared by cutting the magnetic tape MT to a length of 250 mm at a position 30 m to 40 m in the longitudinal direction from one end on the outer circumference of the magnetic tape MT. In this specification, "longitudinal direction" when referring to "from one end on the outer circumference of the magnetic tape MT" means the direction from one end on the outer circumference of the magnetic tape MT toward the other end on the inner circumference. 【0111】 Next, the layers of the sample other than the substrate 41 (i.e., the underlayer 42, magnetic layer 43, and backing layer 44) are removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Then, using a Mitutoyo laser hologage (LGH-110C) as a measuring device, the thickness of the sample (substrate 41) is measured at five points, and the average thickness of the substrate 41 is calculated by simply averaging (arithmetic mean) these measurements. The five measurement points are randomly selected from the sample so that they are all different positions in the longitudinal direction of the magnetic tape MT. 【0112】From the viewpoint of cost reduction, the base material 41 preferably contains a polyester resin as its main component. The polyester resin includes, for example, at least one selected from the group consisting of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene-p (oxybenzoate)), and polyethylene bisphenoxycarboxylate). If the base material 41 contains two or more polyester resins, these two or more polyester resins may be mixed, copolymerized, or laminated. At least one of the terminals and side chains of the polyester resin may be modified. In addition to the polyester resin, the base material 41 may also contain resins other than the polyester resins described later. 【0113】 In this specification, "main component" means the component that has the highest content among the components constituting the substrate 41. For example, if the main component of the substrate 41 is a polyester resin, the content of the polyester resin in the substrate 41 may be, for example, 50% or more by mass, 60% or more by mass, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, or 98% or more by mass relative to the mass of the substrate 41, or the substrate 41 may be composed solely of a polyester resin. 【0114】 The presence of a polyester resin in the substrate 41 can be confirmed, for example, as follows: First, a magnetic tape MT is prepared in the same manner as the method for measuring the average thickness of the substrate 41, cut to a length of 250 mm, and a sample is prepared. Then, layers other than the substrate 41 are removed from the sample. Next, the IR spectrum of the sample (substrate 41) is obtained by infrared absorption spectroscopy (IR). Based on this IR spectrum, it can be confirmed that the substrate 41 contains a polyester resin. 【0115】The substrate 41 preferably contains a polyester resin. By including a polyester resin in the substrate 41, the Young's modulus in the longitudinal direction of the substrate 41 can be reduced, preferably to 2.5 GPa or more and 7.8 GPa or less, more preferably to 3.0 GPa or more and 7.0 GPa or less. Therefore, by adjusting the longitudinal tension of the magnetic tape MT during operation using the recording and playback device, the width of the magnetic tape MT can be kept constant or nearly constant. The method for measuring the Young's modulus in the longitudinal direction of the substrate 41 will be described later. 【0116】 The substrate 41 may contain resins other than polyester resins. In this case, the resins other than polyester resins may be the main components of the constituent materials of the substrate 41. When the resins other than polyester resins are the main components of the constituent materials of the substrate 41, the content of the resins other than polyester resins in the substrate 41 may be, for example, 50% or more by mass, 60% or more by mass, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, or 98% or more by mass relative to the mass of the substrate 41, or the substrate 41 may be composed solely of resins other than polyester resins. The resins other than polyester resins include, for example, at least one selected from the group consisting of polyolefin resins, cellulose derivatives, vinyl resins, and other polymer resins. When the substrate 41 contains two or more of these resins, the two or more materials may be mixed, copolymerized, or laminated. 【0117】 Polyolefin resins include, for example, at least one selected from the group consisting of PE (polyethylene) and PP (polypropylene). Cellulose derivatives include, for example, at least one selected from the group consisting of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and CAP (cellulose acetate propionate). Vinyl resins include, for example, at least one selected from the group consisting of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride). 【0118】Other polymer resins include, for example, at least one selected from the group consisting of PEEK (polyether ether ketone), PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamide imide), aromatic PAI (aromatic polyamide imide), PBO (polybenzoxazole, e.g., Zylon®), polyether, PEK (polyether ketone), polyether ester, PES (polyether sulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane). Specifically, for example, the base material 41 may mainly contain PEEK (polyether ether ketone), PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamide imide), aromatic PAI (aromatic polyamide imide), PBO (polybenzoxazole, e.g., Zylon®), polyether, PEK (polyether ketone), polyether ester, PES (polyether sulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), or PU (polyurethane). 【0119】 The substrate 41 may be biaxially stretched in the longitudinal and width directions. Preferably, the polymer resin contained in the substrate 41 is oriented obliquely to the width direction of the substrate 41. 【0120】 (magnetic layer) 【0121】The magnetic layer 43 is configured to record signals by a magnetization pattern. Preferably, the magnetic layer 43 is a vertical recording type recording layer. The magnetic layer 43 includes, for example, magnetic powder, a binder, carbon particles, and a lubricant. The magnetic layer 43 may further include, if necessary, at least one additive selected from the group consisting of abrasive particles, antistatic agents, hardening agents, rust inhibitors, and non-magnetic reinforcing particles. The magnetic layer 43 may have a plurality of protrusions on the surface (magnetic surface) facing the magnetic layer 43. The plurality of protrusions are formed, for example, by carbon particles and abrasive particles protruding from the magnetic surface. 【0122】 The magnetic layer 43 may have a plurality of pores on its surface. Lubricant may be stored in the pores. In this case, the supply of lubricant to the magnetic surface can be improved. From the viewpoint of improving the supply of lubricant to the magnetic surface, it is preferable that the pores extend perpendicular to the magnetic surface. 【0123】 As shown in Figure 6, the magnetic layer 43 may have a plurality of servo bands SB and a plurality of data bands DB pre-configured. The plurality of servo bands SB are provided at equal intervals in the width direction of the magnetic tape MT. Data bands DB are provided between adjacent servo bands SB. The servo bands SB are for guiding the head unit (magnetic head) 56 (specifically, servo read heads 56A, 56B) when recording or playing back data. Servo patterns (servo signals) for tracking control of the head unit 56 are pre-written to the servo bands SB. User data is recorded in the data bands DB. 【0124】To read the asymmetric servo stripe 113 (see Figure 8) described later, the head unit 56 may be configured to be maintained at an angle with respect to an axis Ax parallel to the width direction of the magnetic tape MT during data recording and playback, as shown in Figure 6. Alternatively, the head unit 56 may be configured to be at an angle with respect to the axis Ax in accordance with the meandering or deformation of the magnetic tape MT during data recording and playback. The inclination angle of the head unit 56 with respect to the axis Ax parallel to the width direction of the magnetic tape MT is preferably 3° to 18°, more preferably 5° to 15°. 【0125】 The total area S of the multiple servo bands SB relative to the area S of the magnetic surface (the surface on the magnetic layer 43 side) ＳＢ Ratio R Ｓ (=(S ＳＢ The upper limit of (S) × 100) is preferably 4.0% or less, more preferably 3.5% or less, and even more preferably 3.0% or less, from the viewpoint of ensuring high recording capacity. On the other hand, the total area S of the multiple servo bands SB relative to the area S of the magnetic surface. ＳＢ Ratio R Ｓ The lower limit is preferably 1.0% or more, from the viewpoint of ensuring a servo band SB of 5 or more. 【0126】 The total area S of multiple servo bands SB relative to the total area S of the magnetic surface ＳＢ Ratio R Ｓ The servobandwidth W is determined as follows: A magnetic tape MT is developed using a ferricolloid developer (Sigma Marker Q, manufactured by Sigma Hi-Chemical Co., Ltd.), and then the developed magnetic tape MT is observed with an optical microscope. ＳＢ Then, measure the number of servo bands SB. Next, calculate the ratio R from the following formula. Ｓ We find the ratio R. Ｓ [%] = (((Servobandwidth W ＳＢ ) × (Number of servo bands SB) / (Width of magnetic tape MT) × 100 【0127】The number of servo bands SB is, for example, 5 + 4n (where n is a non-negative integer) or more. Preferably, the number of servo bands SB is 5 or more, more preferably 9 or more. When the number of servo bands SB is 5 or more, the influence of changes in the width direction of the magnetic tape MT on the servo signal is suppressed, and more stable recording and playback characteristics with fewer off-tracks can be ensured. There is no particular upper limit to the number of servo bands SB, but for example, it is 33 or less. 【0128】 The number of servo bands SB is the ratio R mentioned above. Ｓ It can be calculated in the same way as the calculation method for [another calculation]. 【0129】 Servo bandwidth W ＳＢ The upper limit of the servo bandwidth W is preferably 95 μm or less, more preferably 65 μm or less, and even more preferably 50 μm or less, from the viewpoint of ensuring high recording capacity. ＳＢ The lower limit is preferably 10 μm or more. Servo bandwidth W less than 10 μm ＳＢ A magnetic head capable of reading the servo signal is difficult to manufacture. 【0130】 Servo bandwidth W ＳＢ The width is the ratio R mentioned above. Ｓ It can be calculated in the same way as the calculation method for [another calculation]. 【0131】 As shown in Figure 7A, the magnetic layer 43 is configured to form multiple data tracks Tk in the data band DB. The upper limit of the data track width W is preferably 1200 nm or less, more preferably 1000 nm or less, and even more preferably 850 nm or less, 800 nm or less, or 600 nm or less, from the viewpoint of improving track recording density and ensuring high recording capacity. The lower limit of the data track width W is preferably 20 nm or more, considering the size of the magnetic particles. 【0132】The data track width W is determined as follows. First, a cartridge 10 on which data is recorded across the entire surface of a magnetic tape MT is prepared. The magnetic tape MT is unwound from this cartridge 10, and a 250 mm length of the magnetic tape MT is cut from one end of the outer circumference of the magnetic tape MT at a position 30 m to 40 m in the longitudinal direction to prepare a sample. Next, the data recording pattern of the data band DB portion of the magnetic layer 43 of the sample is observed using a magnetic force microscope (MFM) to obtain an MFM image. For the MFM, Digital Instruments' Dimension ICON and its analysis software are used. The measurement area of ​​the MFM image is set to 10 μm × 10 μm, and this 10 μm × 10 μm measurement area is divided into 512 × 512 (= 262,144) measurement points. Measurements are performed by MFM on three different 10 μm × 10 μm measurement areas, and thus three MFM images are obtained. For each of the three obtained MFM images, the track width is measured at 10 locations, resulting in a total of 30 measurements. The average value (simple average) of these 30 measurements is then calculated. This average value is the data track width W. The analysis software included with the Dimension3100 is used to measure the track width. The MFM measurement conditions are: sweep speed: 1 Hz, chip used: MFMR-20, lift height: 20 nm, correction: Flatten order 3. 【0133】 Although Figure 7A shows an example where adjacent data tracks Tk are recorded without overlapping, the recording method for data tracks Tk is not limited to this example. For example, as shown in Figure 7B, a Shingled Magnetic Recording (SMR) method may be used to record adjacent data tracks Tk so that parts of them overlap in the width direction of the magnetic tape MT. 【0134】 In Figure 7B, heads 61 and 62 represent the recording head and playback head, respectively. In the case of magnetic recording, the data track width W is the recording track width W ＲIt becomes narrower compared to the recording head 61. Therefore, in the case of magnetic recording, the width of the playback head 62 is narrower than the width of the recording head 61. As described above, in the magnetic recording method, the data track width W is narrower than the recording track width W. Ｒ Since it is narrower compared to, it is advantageous in terms of improving recording density. Here, the recording track width W Ｒ This represents the track width during data writing. When magnetic recording is used as the recording method, the recording track width W is used. Ｒ This represents the track width before overwriting (the track width when data is written). 【0135】 The magnetic layer 43 has a minimum value L for the distance between magnetization reversals. min The system is configured to record signals. Minimum value L of the magnetization reversal distance. min The upper limit of is preferably 46.6 nm or less, more preferably 46.3 nm or less, even more preferably 46.2 nm or less, 46.0 nm or less, 44.0 nm or less, 42.3 nm or less, or 40.0 nm or less, from the viewpoint of increasing recording capacity. Minimum value L of the magnetization reversal distance min The lower limit is preferably 20.0 nm or more, taking into account the size of the magnetic particles. 【0136】 Minimum value L of the distance between magnetization reversals minThe following procedure is used to obtain the data track width W. First, a sample is prepared in the same manner as the measurement method for the data track width W. Next, the data recording pattern of the data band DB portion of the magnetic layer 43 of the sample is observed using a magnetic force microscope (MFM) to obtain an MFM image. A Dimension3100 manufactured by Digital Instruments and its analysis software are used as the MFM. The measurement area of ​​the MFM image is set to 2 μm × 2 μm, and this 2 μm × 2 μm measurement area is divided into 512 × 512 (= 262,144) measurement points. Measurements are performed using the MFM on three different 2 μm × 2 μm measurement areas, thus obtaining three MFM images. Fifty inter-bit distances are measured from the two-dimensional relief chart of the recording pattern of the obtained MFM image. These inter-bit distances are measured using the analysis software included with the Dimension3100. The minimum value L of the magnetization reversal distance is the greatest common divisor of the 50 measured inter-bit distances. min The measurement conditions were as follows: sweep speed: 1 Hz, chip used: MFMR-20, lift height: 20 nm, correction: Flatten order 3. 【0137】 The magnetic layer 43 is configured to record signals in the data band DB with a bit length (1 bit length) T. From the viewpoint of improving the linear recording density D of the magnetic tape MT, the upper limit of the bit length T of the signal that can be recorded in the data band DB is preferably 46.6 nm or less, more preferably 46.3 nm or less, even more preferably 46.2 nm or less, 46.0 nm or less, 44.0 nm or less, 42.3 nm or less, or 40.0 nm or less. Considering the size of the magnetic particles, the lower limit of the bit length T of the signal that can be recorded in the data band DB is preferably 20.0 nm or more. 【0138】 The bit length T of the signal that can be recorded in the databand DB is the minimum value L of the magnetization reversal distance. min It can be determined in the same way as the measurement method. 【0139】 From the viewpoint of improving the linear recording density D of the magnetic tape MT, the bit area of ​​the signal that can be recorded in the data band DB is preferably 53,000 nm. ２More preferably, 45,000 nm ２ More preferably, 37,000 nm ２ The following is particularly preferred: 30,000 nm ２ The following applies: 【0140】 The bit area of ​​a signal that can be recorded in the databand DB is determined as follows: First, three MFM images are obtained in the same manner as the method for measuring the data track width W. Next, the data track width W and bit length T are determined in the same manner as the methods for measuring the data track width W and bit length T. Then, the bit area (W × T) of the signal that can be recorded in the databand DB is determined using the data track width W and bit length T. 【0141】 The servo pattern is a magnetized region formed by magnetizing a specific region of the magnetic layer 43 in a specific direction using a servo light head during magnetic tape manufacturing. The region of the servo band SB in which the servo pattern is not formed (hereinafter referred to as the "non-pattern region") may be a magnetized region in which the magnetic layer 43 is magnetized, or it may be a non-magnetized region in which the magnetic layer 43 is not magnetized. If the non-pattern region is a magnetized region, the servo pattern formation region and the non-pattern region are magnetized in different directions (for example, opposite directions). 【0142】 In the LTO standard, the servo band SB has a servo pattern formed on it, consisting of multiple servo stripes (linear magnetized regions) 113 that are inclined with respect to an axis Ax parallel to the width direction of the magnetic tape MT, as shown in Figure 8. 【0143】 The servo band SB includes multiple servo frames 110. Each servo frame 110 consists of 18 servo stripes 113. Specifically, each servo frame 110 consists of a servo subframe 1 (111) and a servo subframe 2 (112). 【0144】The servo subframe 1 (111) consists of an A-burst 111A and a B-burst 111B. The B-burst 111B is positioned adjacent to the A-burst 111A. The A-burst 111A has five servo stripes 113 that are inclined at a predetermined angle θ1 with respect to an axis Ax parallel to the width direction of the magnetic tape MT and are formed at predetermined intervals. In Figure 8, these five servo stripes 113 are labeled A from the EOT (End Of Tape) to the BOT (Beginning Of Tape) of the magnetic tape MT. １ A ２ A ３ A ４ A ５ It is indicated by the notation. 【0145】 The B-burst 111B is equipped with five servo stripes 113 that are inclined at a predetermined angle θ2 with respect to an axis Ax parallel to the width direction of the magnetic tape MT and are formed at predetermined intervals. In Figure 8, these five servo stripes 113 are labeled B from EOT to BOT of the magnetic tape MT. １ , B ２ , B ３ , B ４ , B ５ It is indicated by the notation. 【0146】The servo stripe 113 of the B-burst 111B is inclined in the opposite direction to the servo stripe 113 of the A-burst 111A. The servo stripe 113 of the A-burst 111A and the servo stripe 113 of the B-burst 111B are asymmetrical with respect to the axis Ax, which is parallel to the width direction of the magnetic tape MT. That is, the servo stripe 113 of the A-burst 111A and the servo stripe 113 of the B-burst 111B are arranged in a roughly V-shape. Because the servo stripe 113 of the A-burst 111A and the servo stripe 113 of the B-burst 111B are asymmetrical with respect to the axis Ax, when the head unit 56 is tilted diagonally with respect to the axis Ax, there exists a state in which the servo stripe 113 of the A-burst 111A and the servo stripe 113 of the B-burst 111B are roughly symmetrical with respect to the central axis of the sliding surface of the head unit 56. By changing the tilt of the head unit 56 based on this state, it becomes possible to adjust the distance between the servo lead heads 56A and 56B in the width direction of the magnetic tape MT. Therefore, in both cases where the width of the magnetic tape MT is increased and where the width of the magnetic tape MT is decreased, the servo lead heads 56A and 56B can be positioned to face the specified position of the servo band SB. Note that the central axis of the sliding surface of the head unit 56 refers to the axis that passes through the centers of the multiple servo lead heads 56A and 56B on the sliding surface of the head unit 56. 【0147】The predetermined angle θ1 of the servo stripe 113 of A-burst 111A and the predetermined angle θ2 of the servo stripe 113 of B-burst 111B are different. More specifically, the predetermined angle θ1 of the servo stripe 113 of A-burst 111A may be larger than the predetermined angle θ2 of the servo stripe 113 of B-burst 111B, and the predetermined angle θ2 of the servo stripe 113 of B-burst 111B may be larger than the predetermined angle θ1 of the servo stripe 113 of A-burst 111A. In other words, the inclination of the servo stripe 113 of A-burst 111A may be larger than the inclination of the servo stripe 113 of B-burst 111B, and the inclination of the servo stripe 113 of B-burst 111B may be larger than the inclination of the servo stripe 113 of A-burst 111A. Note that Figure 8 shows an example where the predetermined angle θ1 of the servo stripe 113 of A-burst 111A is larger than the predetermined angle θ2 of the servo stripe 113 of B-burst 111B. The following section will explain the case where the predetermined angle θ1 of the servo stripe 113 of A-burst 111A is larger than the predetermined angle θ2 of the servo stripe 113 of B-burst 111B. 【0148】 The servo subframe 2 (112) consists of a C-burst 112C and a D-burst 112D. The D-burst 112D is positioned adjacent to the C-burst 112C. The C-burst 112C has four servo stripes 113 that are inclined at a predetermined angle θ1 with respect to an axis Ax parallel to the width direction of the magnetic tape MT and are formed at predetermined intervals. In Figure 8, these four servo stripes 113 are labeled C from the EOT to the BOT of the magnetic tape MT. １ , C ２ , C ３ , C ４ It is indicated by the notation. 【0149】 The D-burst 112D is equipped with four servo stripes 113 that are inclined at a predetermined angle θ2 with respect to an axis Ax parallel to the width direction of the magnetic tape MT and are formed at predetermined intervals. In Figure 8, these four servo stripes 113 are labeled D from EOT to BOT of the magnetic tape MT. １ , D２ , D ３ , D ４ It is indicated by the notation. 【0150】 The servo stripe 113 of the D-burst 112D is inclined in the opposite direction to the servo stripe 113 of the C-burst 112C. The servo stripe 113 of the C-burst 112C and the servo stripe 113 of the D-burst 112D are asymmetrical with respect to the axis Ax, which is parallel to the width direction of the magnetic tape MT. That is, the servo stripe 113 of the C-burst 112C and the servo stripe 113 of the D-burst 112D are arranged in a roughly V-shape. Because the servo stripe 113 of the C-burst 112C and the servo stripe 113 of the D-burst 112D are asymmetrical with respect to the axis Ax, when the head unit 56 is tilted diagonally with respect to the axis Ax, there exists a state in which the servo stripe 113 of the C-burst 112C and the servo stripe 113 of the D-burst 112D are roughly symmetrical with respect to the central axis of the head unit 56. By changing the tilt of the head unit 56 based on this state, it becomes possible to adjust the distance between the servos. 【0151】The predetermined angle θ1 of the servo stripe 113 of the C-burst 112C is different from the predetermined angle θ2 of the servo stripe 113 of the D-burst 112D. More specifically, the predetermined angle θ1 of the servo stripe 113 of the C-burst 112C may be larger than the predetermined angle θ2 of the servo stripe 113 of the D-burst 112D, and the predetermined angle θ2 of the servo stripe 113 of the D-burst 112D may be larger than the predetermined angle θ1 of the servo stripe 113 of the C-burst 112C. In other words, the inclination of the servo stripe 113 of the C-burst 112C may be larger than the inclination of the servo stripe 113 of the D-burst 112D, and the inclination of the servo stripe 113 of the D-burst 112D may be larger than the inclination of the servo stripe 113 of the C-burst 112C. Figure 8 shows an example where the predetermined angle θ1 of the servo stripe 113 of the C-burst 112C is larger than the predetermined angle θ2 of the servo stripe 113 of the D-burst 112D. Below, we will explain the case where the predetermined angle θ1 of the servo stripe 113 of the C-burst 112C is larger than the predetermined angle θ2 of the servo stripe 113 of the D-burst 112D. 【0152】 The predetermined angle θ1 of the servo stripe 113 in A burst 111A and C burst 112C is preferably 18° to 28°, more preferably 18° to 26°. The predetermined angle θ2 of the servo stripe 113 in B burst 111B and D burst 112D is preferably -4° to 6°, more preferably -2° to 6°. The servo stripe 113 in A burst 111A and C burst 112C is an example of a first magnetization region. The servo stripe 113 in B burst 111B and D burst 112D is an example of a second magnetization region. 【0153】By reading the servo band SB with the head unit 56, information for obtaining the tape speed and the vertical position of the head unit 56 can be obtained. The tape speed is calculated from the time between four timing signals (A1-C1, A2-C2, A3-C3, A4-C4). The head position is calculated from the time between the aforementioned four timing signals and the time between another four timing signals (A1-B1, A2-B2, A3-B3, A4-B4). The servo pattern may also be a shape that includes two parallel lines. 【0154】 As shown in Figure 8, it is preferable that the servo pattern (i.e., the multiple servo stripes 113) is arranged linearly in the longitudinal direction of the magnetic tape MT. In other words, it is preferable that the servo band SB is linear in the longitudinal direction of the magnetic tape MT. 【0155】 Average thickness t of the magnetic layer 43 ２ The upper limit of the average thickness t2 of the magnetic layer 43 is preferably 0.080 μm or less, more preferably 0.070 μm or less, even more preferably 0.060 μm or less, and particularly preferably 0.050 μm or less. When the upper limit of the average thickness t2 of the magnetic layer 43 is 0.080 μm or less, the effect of the demagnetizing field can be reduced when a ring-type head is used as the recording head, thereby obtaining even better electromagnetic conversion characteristics. 【0156】 Average thickness t of the magnetic layer 43 ２ The lower limit is preferably 0.035 μm or more. Average thickness t of the magnetic layer 43 ２ If the lower limit is 0.035 μm or higher, output can be secured when using an MR type head as the playback head, thus achieving even better electromagnetic conversion characteristics. 【0157】 Average thickness t of the magnetic layer 43 ２The following is how it is obtained. First, the magnetic tape MT housed in the cartridge 10 is unwound, and three samples are prepared by cutting the magnetic tape MT to a length of 250 mm from one end of the outer circumference of the magnetic tape MT at positions 10 m to 20 m, 30 m to 40 m, and 50 m to 60 m in the longitudinal direction. Next, each sample is processed and thinned using the FIB (Focused Ion Beam) method or the like. When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment before observing the TEM image of the cross-section described later. The carbon layer is formed on the surface of the magnetic layer 43 side and the back layer 44 side of the magnetic tape MT by vapor deposition, and the tungsten layer is further formed on the surface of the magnetic layer 43 side by vapor deposition or sputtering. This thinning is performed along the longitudinal direction of the magnetic tape MT. In other words, this thinning process creates a cross-section parallel to both the longitudinal and thickness directions of the magnetic tape MT. 【0158】 The cross-sections of each thinned sample obtained were observed using a transmission electron microscope (TEM) under the following conditions to obtain TEM images of each thinned sample. The magnification and acceleration voltage may be adjusted as appropriate depending on the type of instrument. Instrument: TEM (Hitachi H9000NAR) Acceleration voltage: 300kV Magnification: 100,000x 【0159】 Next, the TEM images of each thinned sample are used to measure the thickness of the magnetic layer 43 at 10 points on each thinned sample. The 10 measurement points on each thinned sample are randomly selected from the sample so that they are all different locations along the longitudinal direction of the magnetic tape MT. The average value obtained by simply averaging (arithmetic mean) the measured values ​​of each thinned sample (a total of 30 points of magnetic layer 43 thickness) is then used to determine the average thickness t of the magnetic layer 43. ２ Let it be [nm]. 【0160】 (Magnetic powder) 【0161】The magnetic powder is the magnetic powder according to the first embodiment described above. Preferably, the magnetic powder is crystal-oriented preferentially in the direction perpendicular to the magnetic tape MT. In this specification, the direction perpendicular to the magnetic tape MT (thickness direction) refers to the thickness direction of the magnetic tape MT. 【0162】 (Binding agent) 【0163】 The binder may include, for example, a thermoplastic resin. The binder may further include a thermosetting resin or a reactive resin, etc. 【0164】 The thermoplastic resin includes, for example, a first thermoplastic resin (first binder) containing chlorine atoms and a second thermoplastic resin (second binder) containing nitrogen atoms. More specifically, the thermoplastic resin includes a vinyl chloride resin and a urethane resin. In this specification, a vinyl chloride resin means a polymer containing structural units derived from vinyl chloride. More specifically, for example, a vinyl chloride resin means a homopolymer of vinyl chloride, a polymer of vinyl chloride and a comonomer copolymerizable therewith, and mixtures of these polymers. 【0165】 The vinyl chloride resin includes, for example, at least one selected from the group consisting of vinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-vinyl chloride-vinylidene chloride copolymer, and methacrylic acid ester-vinyl chloride copolymer. 【0166】 A urethane resin refers to a resin in which at least a portion of the molecular chains constituting the resin contains urethane bonds, and may be a urethane resin or a copolymer in which a portion of the molecular chains contains urethane bonds. A urethane resin may be obtained, for example, by reacting a polyisocyanate with a polyol. Alternatively, a urethane resin may be obtained, for example, by reacting a polyester with a polyol. In this specification, urethane resins also include those obtained by reaction with a curing agent. 【0167】The polyisocyanate includes, for example, at least one selected from the group consisting of diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), 1,5-pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). In this specification, polyisocyanate means a compound having two or more isocyanate groups in its molecule. The polyisocyanate may also be a polyisocyanate contained in the curing agent. 【0168】 Any suitable polyol can be used as the polyol, as long as it has two or more OH groups. The polyol includes, for example, at least one selected from the group consisting of polyols having two OH groups (diols), polyols having three OH groups (triols), polyols having four OH groups (tetraols), polyols having five OH groups (pentaols), and polyols having six OH groups (hexaols). Specifically, the polyol includes, for example, at least one selected from the group consisting of polyester polyols, polyether polyols, polycarbonate polyols, polyesteramide polyols, and acrylate polyols. 【0169】 The polyester includes, for example, at least one selected from the group consisting of phthalate polyesters and aliphatic polyesters. 【0170】The thermoplastic resin may further contain thermoplastic resins other than vinyl chloride resins and urethane resins. Such thermoplastic resins include, for example, at least one selected from the group consisting of vinyl acetate, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene butadiene copolymer, polyester resin, amino resin, and synthetic rubber. 【0171】 The thermosetting resin includes, for example, at least one selected from the group consisting of phenolic resins, epoxy resins, polyurethane curing resins, urea resins, melamine resins, alkyd resins, silicone resins, polyamine resins, and urea-formaldehyde resins. 【0172】 All of the above binders contain -SO4 for the purpose of improving the dispersibility of magnetic particles. ３ M, -OSO ３ M, -COOM, P=O(OM) ２ (However, in the formula, M represents a hydrogen atom or an alkali metal such as lithium, potassium, or sodium) or -NR1R2, -NR1R2R3 ＋ X － Side-chain amines having terminal groups represented by >NR1R2 ＋ X － Main-chain amines represented by (wherein R1, R2, and R3 represent hydrogen atoms or hydrocarbon groups, X － ) represents halogen element ions such as fluorine, chlorine, bromine, and iodine, inorganic ions, or organic ions. ), Furthermore, polar functional groups such as -OH, -SH, -CN, and epoxy groups may be introduced. The amount of these polar functional groups introduced into the binder is 10 －１ The above 10 －８ It is preferable that the amount is 10 moles / g or less.－２ The above 10 －６ It is more preferable that the concentration is 1 / mole / g or less. 【0173】 (Carbon particles) 【0174】 Some of the carbon particles contained in the magnetic layer 43 may protrude from the magnetic surface, forming multiple protrusions. The formation of multiple protrusions by the carbon particles reduces the electrical resistance of the magnetic surface and suppresses static charge on the magnetic surface. In addition, it can reduce dynamic friction between the head unit 56 and the magnetic surface when the magnetic tape MT is running. 【0175】 The carbon particles may also function as an antistatic agent and a solid lubricant. Preferably, the average primary particle size of the carbon particles is 100.0 nm or less. When the average primary particle size of the carbon particles is 100.0 nm or less, even if the carbon particles are particles with a large particle size distribution (e.g., carbon black), the inclusion of particles that are excessively large relative to the thickness of the magnetic layer 43 is suppressed. 【0176】 As carbon particles, one or more selected from the group consisting of carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene can be used, and among these carbon particles, carbon black is preferred. As carbon black, for example, Seest TA manufactured by Tokai Carbon Co., Ltd., Asahi #15, #15HS manufactured by Asahi Carbon Co., Ltd. can be used. 【0177】 The magnetic layer 43 may contain hybrid particles instead of carbon particles, or it may contain hybrid particles together with carbon particles. The hybrid particles include carbon and a material other than carbon. The material other than carbon is, for example, an organic material or an inorganic material. The hybrid particles may be hybrid particles in which carbon is attached to the surface of an inorganic particle. Specifically, for example, they may be hybrid carbon in which carbon is attached to the surface of a silica particle. 【0178】 (Lubricant) 【0179】The lubricant may be a liquid lubricant. The lubricant may include, for example, at least one selected from fatty acids and fatty acid esters, preferably both fatty acids and fatty acid esters. The inclusion of a lubricant in the magnetic layer 43, and in particular the inclusion of both fatty acids and fatty acid esters in the magnetic layer 43, contributes to improving the running stability of the magnetic tape MT. More particularly, good running stability is achieved by the magnetic layer 43 containing a lubricant and having pores. This improvement in running stability is thought to be because the coefficient of dynamic friction on the magnetic layer 43 side surface of the magnetic tape MT is adjusted by the lubricant to a value suitable for the running of the magnetic tape MT. 【0180】 The fatty acid may preferably be a compound represented by the following general formula (1) or (2). For example, the fatty acid may include either the compound represented by the following general formula (1) and the compound represented by the following general formula (2), or both. 【0181】 Furthermore, the fatty acid ester may preferably be a compound represented by the following general formulas (3), (4), or (5). For example, the fatty acid ester may include one, two, or three of the compounds represented by the following general formulas (3), (4), and (5). 【0182】 The lubricant contains either one or both of the compounds shown in general formula (1) and general formula (2), and one, two, or three of the compounds shown in general formula (3), general formula (4), and general formula (5), thereby suppressing the increase in the coefficient of dynamic friction of the magnetic tape MT due to repeated recording or playback. 【0183】 CH3 (CH2) k COOH ... (1) (However, in general formula (1), k is an integer selected from the range of 14 to 22, more preferably from the range of 14 to 18.) 【0184】 CH3 (CH2) n CH = CH(CH2) mCOOH ... (2) (However, in general formula (2), the sum of n and m is an integer selected from the range of 12 to 20, more preferably from the range of 14 to 18.) 【0185】 CH3 (CH2) p COO (CH2) q CH3 ... (3) (However, in general formula (3), p is an integer selected from the range of 14 to 22, more preferably from 14 to 18, and q is an integer selected from the range of 2 to 5, more preferably from 2 to 4.) 【0186】 CH3 (CH2) r COO-(CH2) s CH(CH3)² ... (4) (wherein in general formula (4), r is an integer selected from the range of 14 to 22, and s is an integer selected from the range of 1 to 3.) 【0187】 CH3 (CH2) ｔ COO-(CH)(CH3)CH2(CH3) ｕ ... (5) (However, in general formula (5), t is an integer selected from the range of 14 to 22, and u is an integer selected from the range of 1 to 3.) 【0188】 (abrasive particles) 【0189】 Some of the abrasive particles contained in the magnetic layer 43 may protrude from the magnetic surface, forming multiple protrusions. When the head unit 56 and the magnetic tape MT slide against each other, the protrusions formed by the abrasive particles can come into contact with the head unit 56. 【0190】 The lower limit of the Mohs hardness of the abrasive particles is preferably 7.0 or higher, more preferably 7.5 or higher, even more preferably 8.0 or higher, and particularly preferably 8.5 or higher, from the viewpoint of suppressing deformation due to contact with the head unit 56. The upper limit of the Mohs hardness of the abrasive particles is preferably 9.5 or lower, from the viewpoint of suppressing wear of the head unit 56. 【0191】The abrasive particles are preferably inorganic particles. Examples of inorganic particles include α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, needle-shaped α-iron oxide obtained by dehydrating and annealing raw materials of magnetic iron oxide, surface-treated with aluminum and / or silica as needed, and diamond powder. As inorganic particles, it is preferable to use alumina particles such as α-alumina, β-alumina, and γ-alumina, and silicon carbide. The abrasive particles may be needle-shaped, spherical, cube-shaped, etc., but those with corners on part of their shape are preferred because they have high abrasiveness. 【0192】 (Antistatic agent) 【0193】 Antistatic agents can reduce the electrical resistance of magnetic surfaces and suppress the charging of magnetic surfaces. For example, an antistatic agent may include at least one selected from the group consisting of natural surfactants, nonionic surfactants, and cationic surfactants. 【0194】 (Hardening agent) 【0195】 The curing agent includes, for example, a polyisocyanate. The polyisocyanate may include, for example, diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), 1,5-pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), or isophorone diisocyanate (IPDI) as an isocyanate source. The polyisocyanate may have a TMP adduct structure, an isocyanurate structure, a biuret structure, or an allophanate structure. 【0196】Polyisocyanates specifically include, for example, aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate (HMDI) and active hydrogen compounds. The weight-average molecular weight of these polyisocyanates is preferably in the range of 100 to 3000. 【0197】 (Rust inhibitor) 【0198】 Examples of rust inhibitors include phenols, naphthols, quinones, heterocyclic compounds containing nitrogen atoms, heterocyclic compounds containing oxygen atoms, and heterocyclic compounds containing sulfur atoms. 【0199】 (Non-magnetic reinforced particles) 【0200】 Examples of non-magnetic reinforcing particles include aluminum oxide (α, β, or γ alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, and titanium oxide (rutile or anatase type titanium oxide). 【0201】 (base layer) 【0202】 The base layer 42 is for mitigating the uneven surface shape of the substrate 41 and adjusting the uneven shape of the magnetic surface. The base layer 42 is a non-magnetic layer containing non-magnetic particles, a binder, and a lubricant. The base layer 42 supplies lubricant to the magnetic surface. The base layer 42 may further contain at least one additive selected from the group consisting of antistatic agents, hardening agents, and rust inhibitors, if necessary. 【0203】 The base layer 42 may have a plurality of pores. Lubricant may be stored in the pores. In this case, the supply of lubricant to the magnetic surface can be improved. From the viewpoint of improving the supply of lubricant to the magnetic surface, it is preferable that the pores extend perpendicular to the magnetic surface. From the viewpoint of improving the supply of lubricant to the magnetic surface, it is preferable that the pores of the base layer 42 and the pores of the magnetic layer 43 are connected. 【0204】 Average thickness t of the base layer 42 ３The upper limit is preferably 0.90 μm or less, more preferably 0.80 μm or less, even more preferably 0.70 μm or less, and particularly preferably 0.60 μm or less. Average thickness t of the underlayer 42 ３ If the thickness is 0.90 μm or less, the amount of binder that rises to the magnetic surface can be suppressed. Therefore, the increase in running friction between the head and the magnetic tape MT can be suppressed. Average thickness t of the base layer 42 ３ The lower limit is preferably 0.30 μm or more, from the viewpoint of mitigating the uneven shape on the surface of the substrate 41. 【0205】 Average thickness t of the base layer 42 ３ The average thickness t of the magnetic layer 43 is ２ It is determined in the same manner as above. However, the magnification of the TEM image is adjusted as appropriate according to the thickness of the underlying layer 42. 【0206】 Average thickness t of the substrate 41 １ In contrast, the average thickness t of the magnetic layer 43 ２ and the average thickness t of the base layer 42 ３ If the total thickness is too large, the bending rigidity will increase, which may reduce the stability of the contact between the magnetic tape MT and the head. On the other hand, the average thickness t of the base body 41 １ In contrast, the average thickness t of the magnetic layer 43 ２ and the average thickness t of the base layer 42 ３ If the total thickness is too small, there is a risk that the surface quality of the magnetic surface of the magnetic tape MT will deteriorate. Therefore, the average thickness t of the substrate 41 １ The average thickness t of the magnetic layer 43 relative to this. ２ and the average thickness t of the base layer 42 ３ The ratio of the total thickness ((t) ２ +t ３ ) / t １ ) is preferably 0.19 or more and 0.28 or less. 【0207】Preferably, the base layer 42 has multiple pores. By storing lubricant in these multiple pores, the decrease in the amount of lubricant supplied between the magnetic surface and the head unit 56 can be further suppressed even after repeated recording or playback (i.e., even after repeated running with the head unit 56 in contact with the surface of the magnetic tape MT). Therefore, the increase in the coefficient of dynamic friction can be further suppressed. In other words, even better running stability can be obtained. 【0208】 (Non-magnetic particles) 【0209】 Non-magnetic particles include, for example, at least one of inorganic particles and organic particles. Non-magnetic particles may also be carbon particles such as carbon black. One type of non-magnetic particle may be used alone, or two or more types of non-magnetic particles may be used in combination. Inorganic particles include, for example, metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, or metal sulfides. Examples of non-magnetic particle shapes include, but are not limited to, needle-shaped, spherical, cubic, and plate-shaped particles. 【0210】 (Binding agent, lubricant) 【0211】 The binder and lubricant are the same as those used in the magnetic layer 43 described above. 【0212】 (Additives) 【0213】 The antistatic agent, hardening agent, and rust inhibitor are the same as those described above for the magnetic layer 43. 【0214】 (Back layer) 【0215】 The back layer 44 contains a binder and non-magnetic particles. The back layer 44 may further contain at least one additive selected from the group consisting of lubricants, hardeners, and antistatic agents, if necessary. The binder and non-magnetic particles are the same as those in the base layer 42 described above. The hardener and antistatic agent are the same as those in the magnetic layer 43 described above. 【0216】The average particle size of the non-magnetic particles is preferably 10.0 nm to 150.0 nm, more preferably 15.0 nm to 110.0 nm. The average particle size of the non-magnetic particles is determined in the same manner as the average particle size of the magnetic particles. The non-magnetic particles may include non-magnetic particles having a particle size distribution of 2 or more. 【0217】 Average thickness t of the back layer 44 ４ The upper limit is preferably 0.60 μm or less. Average thickness t of the back layer 44 ４ If the upper limit is 0.60 μm or less, even if the average thickness t of the magnetic tape MT is 5.30 μm or less, the thickness of the base layer 42 and the substrate 41 can be kept thick, thereby maintaining the running stability of the magnetic tape MT within the recording and playback device. Average thickness t of the back layer 44 ４ The lower limit is not particularly restricted, but for example, it is 0.20 μm or larger. 【0218】 Average thickness t of the back layer 44 ４ This can be calculated as follows: First, the average thickness t of the magnetic tape MT. Ｔ Measure the average thickness t. Ｔ The measurement method is as described in "Average Thickness of Magnetic Tape" below. Next, the magnetic tape MT housed in the cartridge 10 is unwound, and a 250 mm length of the magnetic tape MT is cut from one end of the outer circumference of the magnetic tape MT at a position 30 m to 40 m in the longitudinal direction to prepare a sample. Next, the back layer 44 of the sample is removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, the thickness of the sample is measured at five points using a Mitutoyo laser hologage (LGH-110C), and these measurements are simply averaged (arithmetic mean) to obtain the average value t Ｂ The [μm] value is calculated. Then, the average thickness t of the back layer 44 is calculated using the following formula. ４ Determine the [μm]. Note that the five measurement points mentioned above will be randomly selected from the sample so that they are all at different positions along the longitudinal direction of the magnetic tape MT. ４ [μm] = t Ｔ [μm] - t Ｂ [μm] 【0219】 (Lubricant layer) 【0220】 The lubricant layer contains a lubricant, which is the same as the lubricant contained in the magnetic layer 43 described above. The lubricant layer may also be formed by the lubricant supplied to the magnetic surface from the magnetic layer 43 and the underlayer 42. 【0221】 (Average thickness of magnetic tape) 【0222】 Average thickness (average total thickness) of magnetic tape MT: t Ｔ The upper limit is preferably 5.30 μm or less, more preferably 5.10 μm or less, even more preferably 4.90 μm or less, and particularly preferably 4.70 μm or less. Average thickness t of magnetic tape MT Ｔ If the thickness is 5.30 μm or less, the recording capacity that can be recorded in one data cartridge can be increased compared to general magnetic tape. Ｔ The lower limit is not particularly restricted, but for example, it is 3.50 μm or larger. 【0223】 Average thickness t of magnetic tape MT Ｔ The following is how it is determined. First, the magnetic tape MT housed in the cartridge 10 is unwound, and a 250 mm length of the magnetic tape MT is cut from one end of the outer circumference of the magnetic tape MT at a position 30 m to 40 m in the longitudinal direction to prepare a sample. Next, the thickness of the sample is measured at five points using a laser hologage (LGH-110C) manufactured by Mitutoyo as the measuring device, and these measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness t. Ｔ The measurement value in [μm] is calculated. The five measurement points mentioned above are to be randomly selected from the sample so that they are all at different locations along the longitudinal direction of the magnetic tape MT. 【0224】 (Coercive force Hc １ ) 【0225】 Coercivity Hc of the magnetic layer 43 in the vertical direction of the magnetic tape MT １ The upper limit of is preferably 3500 Oe or less, more preferably 3400 Oe or less, and even more preferably 3300 Oe or less. Coercivity Hc of the magnetic layer 43 in the vertical direction of the magnetic tape MT １If the value is 3500e or less, sufficient electromagnetic conversion characteristics can be achieved even at high recording densities. 【0226】 Coercivity Hc of the magnetic layer 43 measured in the vertical direction of the magnetic tape MT １ The lower limit of the coercivity Hc of the magnetic layer 43 measured in the perpendicular direction of the magnetic tape MT is preferably 2500 Oe or more, more preferably 2600 Oe or more, and even more preferably 2700 Oe or more. １ If the value is 2500Oe or higher, demagnetization due to leakage magnetic flux from the recording head can be suppressed. 【0227】 The above coercivity HC １ The following procedure is used to determine the magnetic tape. First, the magnetic tape MT housed in the cartridge 10 is unwound, and six pieces of magnetic tape MT are cut out from one end of the outer circumference of the magnetic tape MT at positions 30m to 40m in the longitudinal direction. At this time, the magnetic tape MT is marked with an arbitrary non-magnetic ink so that the longitudinal direction (direction of travel) of the magnetic tape MT can be recognized. Next, the three cut pieces of magnetic tape MT are stacked together with double-sided tape so that their longitudinal orientations are the same, and then punched out with a φ6.39 mm punch to create a measurement sample. Next, the M-H loop of the measurement sample (the entire magnetic tape MT) corresponding to the vertical direction (thickness direction) of the magnetic tape MT is measured using a vibrating sample magnetometer (VSM). Next, the coatings (underlayer 42, magnetic layer 43, and back layer 44, etc.) of the remaining three cut pieces of magnetic tape MT are wiped off using acetone or ethanol, leaving only the substrate 41. Then, the obtained substrate 41 is stacked in three layers using double-sided tape, and punched out with a φ6.39 mm punch to create a sample for background correction (hereinafter simply referred to as the "correction sample"). Subsequently, the M-H loop of the correction sample (substrate 41) corresponding to the vertical direction of the substrate 41 (the vertical direction of the magnetic tape MT) is measured using a VSM. 【0228】In the measurement of the M-H loop of the measurement sample (the entire magnetic tape MT) and the M-H loop of the correction sample (substrate 41), a high-sensitivity vibration sample type magnetometer "VSM-P7-15 type" manufactured by Toei Industry Co., Ltd. is used. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bit, Time constant of Locking amp: 0.3 sec, Waiting time: 1 sec, MH average number: 20. 【0229】 After obtaining the M-H loop of the measurement sample (the entire magnetic tape MT) and the M-H loop of the correction sample (substrate 41), background correction is performed by subtracting the M-H loop of the correction sample (substrate 41) from the M-H loop of the measurement sample (the entire magnetic tape MT), and an M-H loop after background correction is obtained. For the calculation of this background correction, the measurement / analysis program attached to the "VSM-P7-15 type" is used. The coercive force Hc2 is obtained from the obtained M-H loop after background correction. In addition, for this calculation, the measurement / analysis program attached to the "VSM-P7-15 type" is used. It should be noted that all the above measurements of the M-H loop are carried out at 25°C ± 2°C and 50% RH ± 5% RH. Also, "demagnetizing field correction" is not performed when measuring the M-H loop in the vertical direction of the magnetic tape MT. 【0230】 (Squareness ratio) 【0231】 The lower limit value of the squareness ratio Rs1 of the magnetic layer 43 in the vertical direction of the magnetic tape MT is preferably 62% or more, more preferably 65% or more, still more preferably 68% or more, 72% or more or 75% or more. When the squareness ratio Rs1 is 62% or more, the perpendicular orientation of the magnetic particles becomes sufficiently high, so that the electromagnetic conversion characteristics can be improved. 【0232】When the magnetic powder contains hexagonal ferrite particles, the upper limit value of the squareness ratio Rs1 of the magnetic layer 43 in the vertical direction of the magnetic tape MT is preferably 85% or less, more preferably 80% or less. When the upper limit value of the squareness ratio Rs1 is 85% or less, it is possible to suppress the excessive alignment of the plate surfaces of the hexagonal ferrite particles on the surface of the magnetic layer 43. Therefore, the running friction between the magnetic tape MT and the head can be suppressed. 【0233】 When the magnetic powder contains hexagonal ferrite particles, the numerical range of the squareness ratio Rs1 of the magnetic layer 43 may be defined by any of the above lower limit values and any of the above upper limit values, preferably 62% or more and 85% or less, more preferably 65% or more and 85% or less, still more preferably 68% or more and 85% or less, 72% or more and 80% or less, or 75% or more and 80% or less. 【0234】 The squareness ratio Rs1 in the vertical direction of the magnetic tape MT is obtained as follows. First, a measurement sample is prepared in the same manner as the measurement method of the above coercive force Hc １ . Next, the M-H loop of the measurement sample (the entire magnetic tape MT) corresponding to the vertical direction of the magnetic tape MT (the vertical direction of the magnetic tape MT) is measured using a VSM. Next, a correction sample is prepared in the same manner as the measurement method of the above coercive force Hc １ . Then, the M-H loop of the correction sample (substrate 41) corresponding to the vertical direction of the substrate 41 (the vertical direction of the magnetic tape MT) is measured using a VSM. 【0235】 After the M-H loops of the measurement sample (the entire magnetic tape MT) and the correction sample (substrate 41) are obtained, the M-H loop of the correction sample (substrate 41) is subtracted from the M-H loop of the measurement sample (the entire magnetic tape MT), so that background correction is performed and an M-H loop after background correction is obtained. For the calculation of this background correction, the measurement / analysis program attached to "VSM-P7-15 type" is used. 【0236】The saturation magnetization Ms(emu) and remanent magnetization Mr(emu) of the M-H loop obtained after background correction are substituted into the following formula to calculate the squareness ratio Rs1 (%). Note that all M-H loop measurements above are performed at 25°C ± 2°C and 50% RH ± 5% RH. Furthermore, "demagnetization correction" is not performed when measuring the M-H loop perpendicular to the magnetic tape MT. The measurement and analysis program included with the "VSM-P7-15" is used for this calculation. Squareness ratio Rs1 = (Mr / Ms) 【0237】 The upper limit of the squareness ratio Rs2 of the magnetic layer 43 in the longitudinal direction (travel direction) of the magnetic tape MT is preferably 35% or less, more preferably 30% or less, and even more preferably 29% or less, 25% or less, 20% or less, or 15% or less. When the squareness ratio Rs2 is 35% or less, the vertical orientation of the magnetic particles becomes sufficiently high, which can improve the electromagnetic conversion characteristics. 【0238】 When the magnetic powder contains hexagonal ferrite particles, the lower limit of the squareness ratio Rs2 of the magnetic layer 43 in the longitudinal direction (travel direction) of the magnetic tape MT is preferably 26% or more. When the lower limit of the squareness ratio Rs2 is 26% or more, it is possible to suppress the excessive alignment of the hexagonal ferrite particle plates on the surface of the magnetic layer 43. Therefore, it is possible to suppress the travel friction between the magnetic tape MT and the head. 【0239】 When the magnetic powder contains hexagonal ferrite particles, the numerical range of the squareness ratio Rs2 of the magnetic layer 43 may be defined by either of the above upper limits and the above lower limit, preferably 26% or more and 35% or less, more preferably 26% or more and 30% or less, and even more preferably 26% or more and 29% or less. 【0240】In addition, the angular ratio Rs1 of the magnetic layer 43 in the vertical direction of the magnetic tape MT, and the angular ratio Rs2 of the magnetic layer 43 in the longitudinal direction (travel direction) of the magnetic tape MT, may be within the above preferred range, while the other may be outside the above preferred range. Alternatively, both the angular ratio Rs1 of the magnetic layer 43 in the vertical direction of the magnetic tape MT and the angular ratio Rs2 of the magnetic layer 43 in the longitudinal direction (travel direction) of the magnetic tape MT may be within the above preferred range. 【0241】 The angular ratio Rs2 of the magnetic tape MT in the longitudinal direction is determined in the same manner as the angular ratio Rs1, except that the M-H loop is measured in the longitudinal direction (travel direction) of the magnetic tape MT and the base 41. 【0242】 (Crystal magnetic anisotropy constant K) ｕ ) 【0243】 The crystal magnetic anisotropy constant K of the magnetic recording medium in this technology. ｕ The lower limit is preferably 2.75 × 10 ６ erg / cc or more, more preferably 2.80 × 10 ６ erg / cc or higher, more preferably 2.85 × 10 ６ erg / cc or more, more preferably 2.90 × 10 ６ The erg / cc is greater than or equal to the magnetic anisotropy constant K of the magnetic recording medium. ｕ The upper limit is preferably 3.25 × 10 ６ erg / cc or less, more preferably 3.20 × 10 ６ erg / cc or less, more preferably 3.15 × 10 ６ erg / cc or less, more preferably 3.10 × 10 ６ It is less than or equal to erg / cc. Furthermore, the crystal magnetic anisotropy constant K of the magnetic recording medium. ｕ Preferably 2.75 × 10 ６ erg / cc or more 3.25×10 ６ erg / cc or less, more preferably 2.80 × 10 ６ erg / cc or more 3.20×10 ６ erg / cc or less, more preferably 2.85 × 10 ６ erg / cc or more 3.15×10 ６erg / cc or less, more preferably 2.90 × 10 ６ erg / cc or more 3.10×10 ６ The erg / cc is less than or equal to the crystal magnetic anisotropy constant K of the magnetic recording medium. ｕ However, 2.75 x 10 ６ erg / cc or more 3.25×10 ６ Good thermal stability can be obtained if the erg / cc is within the range of erg / cc or less. Crystal magnetic anisotropy constant K of the above magnetic recording medium ｕ The crystalline magnetic anisotropy constant K of the magnetic powder according to the first embodiment is ｕ It can be calculated using the same method. 【0244】 (Ha full width at half maximum) 【0245】 In the magnetic recording medium of this technology, the full width at half maximum (FWHM) Ha of the main peak of the SFD (Switching Field Distribution) curve is preferably 5000 Oe or less, more preferably 4900 Oe or less, even more preferably 4800 Oe or less, and even more preferably 4700 Oe or less. ａ If the upper limit of the (half-width) is 5000Oe or less, noise in the magnetic tape can be suppressed. 【0246】 H of the above magnetic powder ａ The (full width at half maximum) can be calculated as follows: First, the coercivity Hc mentioned above. １ The M-H loop after background correction is obtained using the same measurement method as above. Next, the SFD curve (differential curve of the M-H loop) is determined from the obtained M-H loop. In the SFD curve of the magnetic recording medium, the full width at half maximum (FMAX) of the main peak is H. ａ H ｃ１ In that case, SFD is H ａ / H ｃ１ This is calculated using the SFD curve and the full width at half maximum (H). ａ The measurement and analysis program included with the "VSM-P7-15" is used for the calculation. 【0247】 (3) Method for manufacturing a magnetic recording medium 【0248】 Next, an example of a method for manufacturing a magnetic recording medium (magnetic tape MT) having the above configuration will be described. 【0249】 (Paint preparation process) 【0250】 First, a primer-forming coating is prepared by kneading and dispersing non-magnetic particles and binders in a solvent. Next, a magnetic layer-forming coating is prepared by kneading and dispersing magnetic powder and binders in a solvent. For the preparation of the magnetic layer-forming coating and the primer-forming coating, for example, the following solvents, dispersion devices, and kneading devices can be used. 【0251】 Examples of solvents used in the preparation of the above-mentioned paints include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol solvents such as methanol, ethanol, and propanol; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol acetate; ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene. These may be used individually or in appropriate mixtures. 【0252】 For the preparation of the paint described above, mixing equipment such as a continuous twin-screw mixer, a continuous twin-screw mixer capable of multi-stage dilution, a kneader, a pressure kneader, and a roll kneader may be used, but the equipment is not limited to these. Furthermore, for the preparation of the paint described above, dispersion equipment such as a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a pearl mill (for example, Eich's "DCP mill"), a homogenizer, and an ultrasonic disperser may be used, but the equipment is not limited to these. 【0253】 (Coating process) 【0254】Next, a base layer 42 is formed by applying a base layer forming paint to one main surface of the substrate 41 and drying it. Subsequently, a magnetic layer forming paint is applied to the base layer 42 and dried it to form a magnetic layer 43 on the base layer 42. During drying, the magnetic particles may be oriented in the thickness direction of the substrate 41 using a magnetic field, for example, a permanent magnet. After the formation of the magnetic layer 43, a back layer 44 is formed on the other main surface of the substrate 41. This yields a magnetic tape MT. The formation order of the base layer 42, magnetic layer 43, and back layer 44 is not limited to the example above. For example, the back layer 44 may be formed on the other main surface of the substrate 41, and then the base layer 42 and magnetic layer 43 may be formed sequentially on one main surface of the substrate 41. 【0255】 The squareness ratios Rs1 and Rs2 can be set to desired values ​​by adjusting, for example, the strength of the magnetic field applied to the coating film of the magnetic layer forming paint, the concentration of solids in the magnetic layer forming paint, and the drying conditions (drying temperature and drying time) of the coating film of the magnetic layer forming paint. The strength of the magnetic field applied to the coating film is preferably two to three times the coercivity of the magnetic particles. To further increase the squareness ratio Rs1 (i.e., to further decrease the squareness ratio Rs2), it is preferable to improve the dispersion state of the magnetic particles in the magnetic layer forming paint. In addition, to further increase the squareness ratio Rs1, it is also effective to magnetize the magnetic particles before the magnetic layer forming paint enters the orientation device for magnetic field orientation of the magnetic particles. The above methods for adjusting the squareness ratios Rs1 and Rs2 may be used individually or in combination of two or more. 【0256】 (Curing process) 【0257】 Next, after winding the magnetic tape MT into a roll, the underlying layer 42 and the magnetic layer 43 are hardened by applying a heat treatment to the magnetic tape MT in this state. 【0258】 (Calendar process) 【0259】 Next, the resulting magnetic tape MT is subjected to calendering to smooth the magnetic surface. 【0260】 (Aging process) 【0261】Next, if necessary, the obtained magnetic tape MT is subjected to an aging process. 【0262】 (Cutting step) 【0263】 Next, the magnetic tape MT is cut to a predetermined width (for example, 1 / 2 inch width). Thus, the magnetic tape MT is obtained. 【0264】 (Servo write step) 【0265】 Next, if necessary, after demagnetizing the magnetic tape MT, a servo pattern may be written on the magnetic tape MT. 【0266】 4. Third Embodiment 【0267】 (1) An embodiment of a magnetic recording cartridge 【0268】 FIG. 18 is an exploded perspective view showing an example of the configuration of the cartridge 10. The cartridge 10 is a one-reel type cartridge, and inside a cartridge case 12 composed of a lower shell 12A and an upper shell 12B, there is one reel 13 around which a tape-shaped magnetic recording medium (hereinafter referred to as "magnetic tape") MT is wound, a reel lock 14 and a reel spring 15 for locking the rotation of the reel 13, a spider 16 for releasing the locked state of the reel 13, a slide door 17 for opening and closing a tape outlet 12C provided in the cartridge case 12 across the lower shell 12A and the upper shell 12B, a door spring 18 for biasing the slide door 17 to the closed position of the tape outlet 12C, a write protect 19 for preventing accidental erasure, and a cartridge memory 11. The reel 13 for winding the magnetic tape MT is substantially disk-shaped with an opening at the center, and is composed of a reel hub 13A and a flange 13B made of a hard material such as plastic. A leader tape LT is connected to the outer peripheral side end of the magnetic tape MT. A leader pin 20 is provided at the tip of the leader tape LT. 【0269】 The cartridge 10 may be a magnetic tape cartridge compliant with the LTO (Linear Tape-Open) standard, or may be a magnetic tape cartridge compliant with a standard different from the LTO standard. 【0270】 The cartridge memory 11 is located near one corner of the cartridge 10. When the cartridge 10 is loaded into the recording / playback device, the cartridge memory 11 faces the reader / writer of the recording / playback device. The cartridge memory 11 communicates with the recording / playback device, specifically the reader / writer, using a wireless communication standard compliant with the LTO standard. 【0271】 5. Experimental Examples 【0272】 The following will provide a more detailed explanation of this technology using experimental examples. However, this technology is not limited in any way to the experimental examples shown below. 【0273】 Table 1 shows the proportions of the raw materials used in the following experimental examples. 【0274】 【0275】 [Investigation of the effect of Nd addition in barium ferrite magnetic powder] 【0276】 Seven types of magnetic powders with different Nd content were prepared, and the relationship between their average particle volume and plate ratio, the relationship between firing temperature and plate ratio, the relationship between saturation magnetization and average particle volume, and the relationship between average particle volume and coercivity were evaluated. 【0277】 [Experimental Example 1-1] 【0278】 (Raw material mixing process) 【0279】 First, neodymium oxide (Nd ２ O ３ ), α iron oxide (Fe ２ O ３ ), barium carbonate (BaCO2) ３ ), strontium carbonate (SrCO ３ ) and titanium dioxide (TiO ２ A mixture of raw materials was obtained by mixing the following in a powder mixer. The proportions of each raw material were as shown in Table 1, proportions 1 to 5. The mixing time was 60 minutes. 【0280】 (melting process) 【0281】Next, 1 kg of the raw material mixture was placed in the crucible of a glass melting furnace and melted to obtain the dissolved product. The melting temperature was 1400°C and the melting time was 80 minutes. During melting, the raw material mixture in the crucible was stirred with a stirring rod rotating at 30 rpm. 【0282】 (Rapid cooling process) 【0283】 Next, an amorphous mass containing crystal nuclei was generated by rapidly cooling the molten material while allowing it to flow out of the crucible. Here, the molten material was rapidly cooled while being rolled using a pair of cooling rolls set to a surface temperature of 20°C. The distance between the pair of cooling rolls was set to 1 mm or less, and the discharge rate was set to between 0.5 g / second and 1.0 g / second. 【0284】 (Grinding process) 【0285】 Next, the amorphous material was ground using a molar mill to obtain an amorphous powder containing crystal nuclei (amorphous particle powder). 【0286】 (Firing process) 【0287】 Next, 30 g of amorphous powder from formulation 1 was placed in a crucible, and the crucible was placed in a muffle furnace for firing. No spacers were placed between the bottom of the crucible and the bottom of the heating chamber. A rectangular crucible made of alumina, measuring 15 cm in length, 15 cm in width, and 7 cm in height, was used. The firing process was carried out as shown below. The furnace was heated from room temperature to a firing temperature of 600°C at a heating rate of 5°C / min. The firing temperature of 600°C was maintained for 8 hours (firing time) from the point where it was reached. After that, the heater of the muffle furnace was stopped, and the muffle furnace door was closed and left as is. Then, after waiting for the temperature inside the furnace to drop sufficiently, the fired body containing barium ferrite particles was removed from the muffle furnace. Here, the firing temperature described in the firing process represents the set temperature of the firing furnace. Similarly, in subsequent experimental examples, the firing temperature described in the firing process represents the set temperature of the firing furnace. Similarly, a fired body containing barium ferrite particles was obtained in the same manner, except that the firing temperatures of 30 g of amorphous powders of formulations 2, 3, 4, and 5 were changed to 610°C, 610°C, 620°C, and 620°C, respectively. 【0288】(Acid treatment and washing process) 【0289】 Next, the resulting calcined body was subjected to an acid treatment to remove the glass components and extract barium ferrite particle powder. The acid treatment was carried out by immersing the calcined body in acetic acid and washing it with a ball mill. Then, the extracted barium ferrite particle powder was washed with pure water. 【0290】 (Separation process) 【0291】 Subsequently, barium ferrite particle powder was obtained by centrifugation using a centrifuge and decantation. 【0292】 (drying process) 【0293】 Finally, the barium ferrite particle powder was placed in an electric furnace and dried at 120°C until its moisture content was 2.0 (wt%) or less. This yielded the desired barium ferrite magnetic powder. 【0294】 [Experimental Example 1-2] 【0295】 Barium ferrite magnetic powder was obtained by carrying out the processes other than the firing process in the same manner as in Experimental Example 1-1. The firing process in Experimental Example 1-2 is as follows. 【0296】 (Firing process) 【0297】 The firing process was carried out in the same manner as in Experimental Example 1-1, except that the firing temperature was changed from 590°C to 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, and 660°C. 【0298】 [evaluation] 【0299】 The average particle volume and plate ratio of the magnetic powder in Experimental Examples 1-1 and 1-2 were determined by calculating the XRD volume of the magnetic powder using XRD (X-ray Diffraction) measurement results, as described in the first embodiment above, and then converting it to TEM volume. The evaluation results are shown in Tables 2 and 3. Figure 9 shows the relationship between the average particle volume and plate ratio in Experimental Example 1-1. Figure 10 shows the relationship between the firing temperature and plate ratio in Experimental Example 1-2. 【0300】 【0301】 【0302】 From the results of Experimental Example 1-1, it can be seen that regardless of the average particle volume of the magnetic powder, increasing the Nd ratio (Nd / Fe atomic ratio, Nd content (%)) decreases the plate-like ratio, and decreasing the Nd ratio (Nd / Fe atomic ratio, Nd content (%)) increases the plate-like ratio. Furthermore, from the results of Experimental Example 1-2, it can be seen that regardless of the firing temperature, increasing the Nd ratio (Nd / Fe atomic ratio, Nd content (%)) decreases the plate-like ratio, and decreasing the Nd ratio (Nd / Fe atomic ratio, Nd content (%)) increases the plate-like ratio. In other words, it can be seen that the plate-like ratio (shape magnetic anisotropy) of magnetic powder can be controlled by adding Nd. 【0303】 [Experimental Examples 1-3] 【0304】 Barium ferrite magnetic powder was obtained by carrying out the processes other than the firing process in the same manner as in Experimental Example 1-2. The firing process in Experimental Example 1-3 is as follows. 【0305】 (Firing process) 【0306】A calcination process was carried out in the same manner as in Experimental Example 1-2, except that the calcination temperature of 30 g of amorphous powder of formulation 1 was changed to 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, and 660°C, respectively, to obtain a calcined body containing barium ferrite particles. A calcination process was carried out in the same manner as in Experimental Example 1-2, except that the calcination temperature of 30 g of amorphous powder of formulation 2 was changed to 600°C, 610°C, 620°C, 630°C, and 640°C, respectively, to obtain a calcined body containing barium ferrite particles. A calcination process was carried out in the same manner as in Experimental Example 1-2, except that the calcination temperature of 30 g of amorphous powder of formulation 3 was changed to 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, and 660°C, respectively, to obtain a calcined body containing barium ferrite particles. The calcination process was carried out in the same manner as in Experimental Example 1-2, except that the calcination temperature of 30 g of amorphous powder of formulation 4 was changed to 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, and 660°C, respectively, to obtain a calcined body containing barium ferrite particles. The calcination process was carried out in the same manner as in Experimental Example 1-2, except that the calcination temperature of 30 g of amorphous powder of formulation 5 was changed to 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, and 660°C, respectively, to obtain a calcined body containing barium ferrite particles. 【0307】 [evaluation] 【0308】 Next, the magnetic properties of the magnetic powder (saturation magnetization σs, coercivity H) ｃ The aspect ratio Rs, SFD, and half-width Ha were evaluated. The magnetic properties were determined by the method described in the first embodiment above. The evaluation results are shown in Table 4. Figure 11 shows the relationship between saturation magnetization σs and average particle volume. Figure 12 shows the relationship between average particle volume and coercivity H ｃ This shows the relationship. 【0309】 【0310】 From the results of Experimental Examples 1-3, it was found that as the amount of Nd added (Nd / Fe atomic ratio, Nd charge (%)) increases, the average particle volume of the magnetic powder and the coercivity H increase. ｃ It can be seen that a large saturation magnetization σs can be obtained even when the average particle volume is reduced without changing the relationship, and thus the magnetic anisotropy energy can be increased. 【0311】[Experimental Examples 1-4] 【0312】 Barium ferrite magnetic powder was obtained by using raw material mixtures of proportions 0 to 5 and carrying out all steps except the calcination process in the same manner as in Experimental Example 1-1. The calcination process in Experimental Example 1-4 is as follows. 【0313】 (Firing process) 【0314】 The calcination process was carried out in the same manner as in Experimental Example 1-1, except that the calcination temperatures of 30 g each of amorphous powders of formulations 0, 1, 2, 3, 4, and 5 were changed to 600°C, 610°C, 610°C, 620°C, 630°C, and 640°C, respectively, to obtain a calcined body containing barium ferrite particles. 【0315】 [evaluation] 【0316】 Next, the thermal stability of magnetic powder (K ｕ V / k Ｂ T, crystal magnetic anisotropy constant K ｕ The following was evaluated: Thermal stability was determined by the method described in the first embodiment above. The evaluation results are shown in Table 5 and Figure 13. Figure 13 shows the Nd addition amount and K ｕ V / K Ｂ This diagram shows the relationship of T. 【0317】 【0318】 The results from Experimental Examples 1-4 show that increasing the amount of Nd added improves thermal stability. Furthermore, it can be seen that the magnetic powders of Examples 1-5, in which the Nd / Fe atomic ratio is in the range of 0.0002 to 0.0050, can improve thermal stability. 【0319】 [Experimental Examples 1-5] 【0320】 Barium ferrite magnetic powder was obtained by using raw material mixtures of proportions 0 to 7 and carrying out all steps except the calcination process in the same manner as in Experimental Example 1-1. The calcination process in Experimental Example 1-5 is as follows. 【0321】 (Firing process) 【0322】The firing temperature for 30g of amorphous powder in formulation 0 was changed to 600°C, 610°C, 620°C, and 630°C. The firing temperature for 30g of amorphous powder in formulation 1 was changed to 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, and 660°C. The firing temperature for 30g of amorphous powder in formulation 2 was changed to 600°C, 610°C, 620°C, 630°C, and 640°C. The firing temperature for 30g of amorphous powder in formulation 3 was changed to 600°C, 610°C, and 6 Except for changing the firing temperatures to 20°C, 630°C, 640°C, 650°C, and 660°C, changing the firing temperature of 30g of amorphous powder in formulation 4 to 600°C, 610°C, 620°C, 630°C, 640°C, and 650°C, and changing the firing temperature of 30g of amorphous powder in formulation 5 to 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, and 660°C, the firing process was carried out in the same manner as in Experimental Example 1-1 to obtain a fired body containing barium ferrite particles. Similarly, except for changing the firing temperatures of 30g of amorphous powder in formulations 6-7 to 650°C, 660°C, 670°C, 680°C, and 690°C respectively, the firing process was carried out in the same manner as in Experimental Example 1-1 to obtain a fired body containing barium ferrite particles. 【0323】 [evaluation] 【0324】 Next, the firing temperature and coercivity H of the magnetic powder. ｃ The relationship between firing temperature and angular ratio Rs, and the relationship between firing temperature and saturation magnetization σs were evaluated. Coercivity H ｃ The angularity ratio Rs and saturation magnetization σs were determined by the method described in the first embodiment above. The evaluation results are shown in Figures 14, 15, and 16. Figure 14 shows the firing temperature and coercivity H of the magnetic powder. ｃ This figure shows the relationship between the firing temperature of the magnetic powder and the square ratio Rs. Figure 16 shows the relationship between the firing temperature of the magnetic powder and the saturation magnetization σs. 【0325】 From the results of Experimental Examples 1-5, when the amount of Nd added increases and the atomic ratio of Nd to Fe (Nd / Fe) becomes 0.0481 (8.00% Nd added) or higher, the saturation magnetization σs becomes less than 49.5 emu / g. Also, unlike the case where the atomic ratio of Nd (Nd / Fe) is 0.0042 (5.00% Nd added) or lower, the firing temperature and the coercivity H after washing are different. ｃIt can be seen that the transitions of the angularity ratio Rs and the saturation magnetization σs are different. Figure 17 shows the results of XRD measurements of the sintered bodies obtained in Experimental Examples 1-4 and 1-5. As shown in Figure 17, there is no clear difference in phase until the atomic ratio of Nd to Fe (Nd / Fe) is 0.0042 (5.00% Nd added) or less, and a clear difference in phase exists when the atomic ratio of Nd to Fe (Nd / Fe) is 0.0481 (8.00% Nd added) or more. This suggests that the hexagonal ferrite crystal structure is maintained while Nd is added until the atomic ratio of Nd to Fe (Nd / Fe) is 0.0042 (5.00% Nd added) or less. 【0326】 [Experimental Examples 1-6] 【0327】 [Example 1] 【0328】 <Preparation process for coatings for forming magnetic layers> 【0329】 The magnetic layer-forming coating containing the magnetic powder of Example 2 in Experimental Examples 1-4 was prepared as follows. First, the first composition with the following formulation was kneaded in an extruder. Next, the kneaded first composition was pre-mixed in a stirring tank equipped with a disperser. Subsequently, the second and third compositions with the following formulations were added and mixed using a dynomill, followed by filtration to prepare the magnetic layer-forming coating. 【0330】 (First composition) 【0331】 Barium ferrite (Ba 0.55 Sr 0.45 Fe １２ O １９ Nd 0.037 ) Magnetic powder (hexagonal plate shape, average plate ratio 2.6, average particle volume 1300 nm) ３): 100 parts by mass, vinyl chloride resin (cyclohexanone solution 30% by mass): 30 parts by mass (degree of polymerization 300, Mn = 10000, contains OSO3K = 0.07 mmol / g and secondary OH = 0.3 mmol / g as polar groups), polyurethane resin (resin solution: polyurethane resin content 30% by mass, cyclohexanone content 70% by mass): 29 parts by mass (polyurethane resin: number average molecular weight Mn = 20000, Tg 100℃), phenylphosphonic acid: 3 parts by mass, n-butyl stearate: 2 parts by mass, methyl ethyl ketone: 220.0 parts by mass, toluene: 120.0 parts by mass, cyclohexanone: 200.0 parts by mass 【0332】 (Second composition) 【0333】 - Aluminum oxide powder: 4.0 parts by mass (α-Al ２ O ３ (Average particle size 100 nm) • Vinyl chloride resin (cyclohexanone solution 30% by mass): 3.0 parts by mass (degree of polymerization 300, Mn = 10000, containing OSO3K = 0.07 mmol / g and secondary OH = 0.3 mmol / g as polar groups.) 【0334】 (Third composition) 【0335】 - Carbon black: 2.0 parts by mass (manufactured by Tokai Carbon Co., Ltd., product name: Seest S, arithmetic mean particle size 70 nm) - Polyurethane resin (resin solution: polyurethane resin content 30% by mass, cyclohexanone content 70% by mass): 4.0 parts by mass (polyurethane resin: number average molecular weight Mn = 20000, Tg 100℃) 【0336】 Finally, to the magnetic layer-forming coating prepared as described above, 3.0 parts by mass of curing agent A and 2.0 parts by mass of stearic acid were added. 【0337】 <Preparation process for coatings for forming a non-magnetic layer> 【0338】 A coating for forming a non-magnetic layer was prepared as follows. First, the fourth composition with the following formulation was kneaded in an extruder. Next, the kneaded fourth composition and the fifth composition with the following formulation were added to a stirring tank equipped with a disperser and pre-mixed. Subsequently, dynomill mixing was performed, followed by filtration to prepare the coating for forming a non-magnetic layer. 【0339】 (Fourth composition) 【0340】 Needle-shaped iron oxide powder: 100 parts by mass (α-Fe ２ O ３ (Average long axis length 0.11 μm) ・Vinyl chloride resin (cyclohexanone solution 30% by mass): 40 parts by mass (degree of polymerization 300, Mn = 10000, contains OSO3K = 0.07 mmol / g and secondary OH = 0.3 mmol / g as polar groups.) ・Aluminum oxide powder: 4 parts by mass (α-Al ２ O ３ , average particle size 0.1μm) 【0341】 (Fifth composition) 【0342】 • Carbon black: 30 parts by mass (manufactured by Asahi Carbon Co., Ltd., product name: #80) • Polyurethane resin (resin solution: polyurethane resin content 30% by mass, cyclohexanone content 70% by mass): 45 parts by mass (polyurethane resin: number average molecular weight Mn = 25000, Tg 70℃) • n-butyl stearate: 2 parts by mass • Methyl ethyl ketone: 130.0 parts by mass • Toluene: 70.0 parts by mass • Cyclohexanone: 80.0 parts by mass 【0343】 Finally, to the non-magnetic layer forming coating prepared as described above, 3.0 parts by mass of curing agent A and 2.0 parts by mass of stearic acid were added. 【0344】 <Preparation process for coating for back layer formation> 【0345】 The coating for forming the back layer was prepared as follows: The following raw materials were mixed in a stirring tank equipped with a disperser, and then filtered to prepare the coating for forming the back layer. 【0346】 • Carbon black (manufactured by Asahi Carbon Co., Ltd., product name: #80): 100 parts by mass • Polyester polyurethane: 35 parts by mass (manufactured by Nippon Polyurethane Co., Ltd., product name: N-2304) • Nitrocellulose (H 1 / 2): 15 parts by mass (manufactured by Inabata Sangyo Co., Ltd., DHX 40-70) • Methyl ethyl ketone: 400 parts by mass • Toluene: 250 parts by mass • Cyclohexanone: 100 parts by mass • Hardener A: 10 parts by mass 【0347】 <Film formation process> 【0348】 Using the paint prepared as described above, a magnetic tape was manufactured as described below. 【0349】 First, a long PEN film (base film) with an average thickness of 4.0 μm was prepared as a support to serve as the base layer of the magnetic tape. Next, a non-magnetic layer was formed on one main surface of the PEN film by applying a coating for forming a non-magnetic layer and drying it, so that the average thickness of the final product would be 0.85 μm. Next, a magnetic layer was formed on the non-magnetic layer by applying a coating for forming a magnetic layer and drying it, so that the average thickness of the final product would be 0.07 μm. In the magnetic recording medium of this embodiment formed by the above film formation process, one or more layers are formed by the magnetic layer and the non-magnetic layer. 【0350】 Next, a back layer forming coating was applied to the other main surface of the PEN film on which the non-magnetic and magnetic layers were formed, and dried to form a back layer such that the average thickness of the final product was 0.35 μm. Then, the PEN film with the non-magnetic layer, magnetic layer, and back layer formed was subjected to a curing treatment at 65°C for 40 hours. After that, calendering was performed to smooth the surface of the magnetic layer. 【0351】 <Cutting process> 【0352】 The magnetic recording medium obtained as described above was cut into strips with a width of 1 / 2 inch (12.65 mm). This resulted in a long, rectangular magnetic tape. 【0353】 [Example 2] 【0354】 A magnetic tape was obtained in the same manner as in Example 1, except that in the preparation step of the coating for forming the magnetic layer, the coating for forming the magnetic layer containing the magnetic powder of Example 5 in Experimental Examples 1-4 was used. 【0355】 [Comparative Example 1] 【0356】 A magnetic tape was obtained in the same manner as in Example 1, except that in the preparation step of the coating for forming the magnetic layer, the coating for forming the magnetic layer containing the magnetic powder of Comparative Example 1 of Experimental Examples 1-4 was used. 【0357】 The magnetic tapes obtained as described above were evaluated as follows: 【0358】 [Crystal magnetic anisotropy constant K] ｕ ] 【0359】 The crystal magnetic anisotropy constant K of the magnetic recording medium described in the second embodiment above. ｕ The measurement method determines the crystalline magnetic anisotropy constant K of the magnetic tape. ｕ The following measurements were taken. The results are shown in Table 6. 【0360】 [Coercivity H in the vertical direction] ｃ ] 【0361】 The coercivity H of the magnetic recording medium described in the second embodiment above. ｃ The coercivity H of the magnetic tape is determined by the measurement method. ｃ The following measurements were taken. The results are shown in Table 6. 【0362】 [Ratio of sides in the vertical direction Rs1] 【0363】 The angular ratio Rs1 in the vertical direction of the magnetic tape was measured using the method for measuring the angular ratio Rs1 of the magnetic recording medium in the vertical direction described in the second embodiment above. The results are shown in Table 6. 【0364】 【0365】 In Examples 1 and 2, the Nd / Fe atomic ratio is 0.0002 or higher, therefore the crystal magnetic anisotropy constant K ｕ is 2.8 x 10 ６ Because the erg / cc is above this level, it has excellent thermal stability. 【0366】This technology can also employ the following configurations: [1] A magnetic powder comprising hexagonal ferrite particles containing Fe, Ba, Sr, and Nd, wherein the atomic ratio of Nd to Fe (Nd / Fe) is 0.0002 or more and 0.0050 or less, and the atomic ratio of Sr to Ba (Sr / Ba) is 0.6 or more and 1.0 or less. [2] The magnetic powder according to [1], further comprising at least one selected from the group consisting of Ti, Mn, Zr, and Sn. [3] The magnetic powder according to [1] or [2], wherein the average plate diameter is 8.0 nm or more and 20.0 nm or less. [4] The magnetic powder according to any one of [1] to [3], wherein the average plate ratio (ratio of the average plate diameter of the magnetic powder to the average plate thickness of the magnetic powder) is 1.0 or more and 3.0 or less. [5] The average particle volume is 200 nm. ３ 1600nm or more ３ The magnetic powder described in any one of the following [1] to [4]: ​​[6] Crystal magnetic anisotropy constant K ｕ is 2.20 × 10 ６ erg / cc or more 2.70×10 ６ A magnetic powder according to any one of [1] to [5], having a value of erg / cc or less. [7] Thermal stability (K ｕ V ａｃｔ / k Ｂ T, K ｕ : The crystalline magnetic anisotropy constant of magnetic powder, V ａｃｔ : Activation volume of magnetic powder, k Ｂ [1] to [6] The magnetic powder described in any one of the following, where : Boltzmann constant, T: absolute temperature is 60 or greater. [8] The magnetic powder described in any one of the following, where SFD (Switching Field Distribution) is 0.5 or greater and 1.5 or less. [9] H ｃThe magnetic powder according to any one of [1] to [8], wherein the coercivity is 2200 Oe or more and 2700 Oe or less.

[10] The magnetic powder according to any one of [1] to [9], wherein the saturation magnetization (σs) is 49.5 emu / g or more and 54.0 emu / g or less.

[11] The magnetic powder according to any one of [1] to

[10] , wherein the full width at half maximum Ha of the main peak of the SFD (Switching Field Distribution) curve is 4000 Oe or less.

[12] A magnetic recording medium having a magnetic layer containing magnetic powder, wherein the magnetic powder contains hexagonal ferrite particles comprising Fe, Ba, Sr, and Nd, the atomic ratio of Nd to Fe (Nd / Fe) is 0.0002 or more and 0.0050 or less, and the atomic ratio of Sr to Ba (Sr / Ba) is 0.6 or more and 1.0 or less.

[13] The magnetic recording medium according to

[12] , wherein the magnetic powder further contains at least one selected from the group consisting of Ti, Mn, Zr, and Sn.

[14] The magnetic recording medium according to

[12] or

[13] , wherein the average plate diameter of the magnetic powder is 8.0 nm or more and 20.0 nm or less.

[15] The magnetic recording medium according to any one of

[12] to

[14] , wherein the average plate ratio of the magnetic powder (ratio of the average plate diameter of the magnetic powder to the average plate thickness of the magnetic powder) is 1.0 or more and 3.0 or less.

[16] The average particle volume of the magnetic powder is 200 nm ３ 1600nm or more ３ A magnetic recording medium described in any one of the following

[12] to

[15] .

[17] Crystal magnetic anisotropy constant K ｕ However, 2.75 x 10 ６ erg / cc or more 3.25×10 ６ A magnetic recording medium according to any one of

[12] to

[16] , wherein the erg / cc is 0.5 or more and 1.5 or less.

[18] A magnetic recording medium according to any one of

[12] to

[17] , wherein the SFD (Switching Field Distribution) of the magnetic powder is 0.5 or more and 1.5 or less.

[19] H in the vertical direction ｃA magnetic recording medium according to any one of

[12] to

[18] , wherein the coercivity is 2500 Oe or more and 3500 Oe or less.

[20] A magnetic recording medium according to any one of

[12] to

[19] , wherein the full width at half maximum Ha of the main peak of the SFD (Switching Field Distribution) curve is 5000 Oe or less. 【0367】 Although embodiments and examples of this technology have been described in detail above, this technology is not limited to the embodiments and examples described above, and various modifications based on the technical concept of this technology are possible. 【0368】 For example, the configurations, methods, processes, shapes, materials, and numerical values ​​listed in the above embodiments and examples are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values ​​may be used as needed. Furthermore, the chemical formulas of compounds are representative examples, and the general name of the same compound is not limited to those listed. 【0369】 Furthermore, the configurations, methods, processes, shapes, materials, and numerical values ​​of the above-described embodiments and examples can be combined with each other, as long as they do not deviate from the spirit of this technology. 【0370】 Furthermore, in this specification, numerical ranges indicated using "~" represent a range that includes the numbers listed before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit of one step in the numerical range may be replaced with the upper or lower limit of another step in the numerical range. Unless otherwise specified, the materials exemplified in this specification may be used individually or in combination of two or more. 【0371】 MT Magnetic recording medium 41 Substrate (base layer) 42 Underlayer 43 Magnetic layer 44 Back layer

Claims

1. A magnetic powder comprising hexagonal ferrite particles containing Fe, Ba, Sr, and Nd, wherein the atomic ratio of Nd to Fe (Nd / Fe) is 0.0002 or more and 0.0050 or less, and the atomic ratio of Sr to Ba (Sr / Ba) is 0.6 or more and 1.0 or less.

2. The magnetic powder according to claim 1, wherein the magnetic powder further contains at least one selected from the group consisting of Ti, Mn, Zr, and Sn.

3. The magnetic powder according to claim 1, wherein the average plate diameter is 8.0 nm or more and 20.0 nm or less.

4. The magnetic powder according to claim 1, wherein the average plate ratio (ratio of the average plate diameter of the magnetic powder to the average plate thickness of the magnetic powder) is 1.0 or more and 3.0 or less.

5. The average particle volume is 200 nm. ３ 1600nm or more ３ The magnetic powder according to claim 1, which is as follows:

6. Crystal magnetic anisotropy constant K ｕ is 2.20 × 10 ６ erg / cc or more 2.70×10 ６ The magnetic powder according to claim 1, wherein the erg / cc is less than or equal to erg / cc.

7. Thermal stability (K ｕ V ａｃｔ / k Ｂ T, K ｕ : Crystalline magnetic anisotropy constant of the magnetic powder, V ａｃｔ : Activation volume of the magnetic powder, k Ｂ : Boltzmann constant, T: absolute temperature) is 60 or more, the magnetic powder according to claim 1.

8. The magnetic powder according to claim 1, wherein the SFD (Switching Field Distribution) is 0.5 or more and 1.5 or less.

9. H ｃ The magnetic powder according to claim 1, wherein the coercivity is 2200 Oe or more and 2700 Oe or less.

10. The magnetic powder according to claim 1, wherein the saturation magnetization (σs) is 49.5 emu / g or more and 54.0 emu / g or less.

11. The magnetic powder according to claim 1, wherein the full width at half maximum Ha of the main peak of the SFD (Switching Field Distribution) curve is 4000 Oe or less.

12. A magnetic recording medium having a magnetic layer containing magnetic powder, wherein the magnetic powder contains hexagonal ferrite particles comprising Fe, Ba, Sr, and Nd, the atomic ratio of Nd to Fe (Nd / Fe) being 0.0002 or more and 0.0050 or less, and the atomic ratio of Sr to Ba (Sr / Ba) being 0.6 or more and 1.0 or less.

13. The magnetic recording medium according to claim 12, wherein the magnetic powder further contains at least one selected from the group consisting of Ti, Mn, Zr, and Sn.

14. The magnetic recording medium according to claim 12, wherein the average plate diameter of the magnetic powder is 8.0 nm or more and 20.0 nm or less.

15. The magnetic recording medium according to claim 12, wherein the average plate-like ratio of the magnetic powder (the ratio of the average plate diameter of the magnetic powder to the average plate thickness of the magnetic powder) is 1.0 or more and 3.0 or less.

16. The average particle volume of the magnetic powder is 200 nm. ３ 1600nm or more ３ The magnetic recording medium according to claim 12, which is as follows:

17. Crystal magnetic anisotropy constant K ｕ However, 2.75 x 10 ６ erg / cc or more 3.25×10 ６ The magnetic recording medium according to claim 12, wherein the erg / cc is less than or equal to erg / cc.

18. The magnetic recording medium according to claim 12, wherein the SFD (Switching Field Distribution) of the magnetic powder is 0.5 or more and 1.5 or less.

19. H in the vertical direction ｃ The magnetic recording medium according to claim 12, wherein the coercivity is 2500 Oe or more and 3500 Oe or less.

20. The magnetic recording medium according to claim 12, wherein the full width at half maximum Ha of the main peak of the SFD (Switching Field Distribution) curve is 5000 Oe or less.

Images