MAGNETIC RECORDING MEDIUM

Abstract

A tape-shaped magnetic recording medium (10) comprising: a base (11); and a magnetic layer (13) provided on the base (11) and containing a magnetic powder, wherein an average particle volume V of the magnetic powder 2000 nm 3 or less, an average thickness of the magnetic recording medium is 5.3 µm or less, a thermal stability K u V act / k B T of the magnetic recording medium is 60 or more and a ratio Hrp / Hc1 of a residual coercive force Hrp of the magnetic recording medium (10) measured using a pulsed magnetic field to a coercive force Hc1 of the magnetic recording medium (10) in the perpendicular direction is 2.10 or less.

Description

Technical field

[0001] The present invention relates to a magnetic recording medium. State of the art

[0002] For example, with the development of IoT, big data, and artificial intelligence, the amount of data collected and stored has increased significantly. Magnetic recording media are often used as a medium for recording large amounts of data.

[0003] Various technologies have been proposed so far regarding a magnetic recording medium.For example, the following Patent Document 1 discloses, as a technology related to a magnetic powder contained in a magnetic recording medium, a magnetic recording medium having at least one magnetic layer formed by applying a magnetic coating material containing a ferromagnetic powder and a binder on a non-magnetic support, the magnetic recording medium being characterized in that the magnetic layer contains an aromatic compound in an amount of 0.4 [parts by weight] to 10 [parts by weight] based on 100 [parts by weight] of the ferromagnetic powder, the aromatic compound having a carboxyl group and at least one or more hydroxyl groups in the molecule, and having a condensed ring if the number of aromatic rings is two or more.

[0004] Magnetic recording media are known, for example, from the following patent documents JP 2014 - 170 604 A, JP 6 610 828 B1, JP 6 635 224 B1, JP 6 645 613 B1, JP 6 635 220 B1, JP 2002 - 373 413 A and US 11 626 128 B2.

[0005] A method for emulating a magnetic recording channel is known from the scientific article OKAZAKI, Yutaka: An error rate emulation system, in: IEEE transactions on magnetics, Vol. 31, 1995, No. 6, pp. 3093-3095. - ISSN 0018-9464. Citation listPatent document

[0006] Patent Document 1: Japanese Patent Laid-Open No. 2002-373413 Disclosure of the inventionTechnical problem

[0007] To improve the recording density of the magnetic recording medium, it is conceivable to reduce the particle volume of the magnetic powder contained in the magnetic recording medium. However, as the particle volume of the magnetic powder decreases, the preservation stability of the magnetic recording medium decreases. This reduction in preservation stability can be particularly problematic in the case where the magnetic recording medium is preserved for extended periods of time.

[0008] In this regard, a main object of the present disclosure is to provide a magnetic recording medium having excellent preservation stability even in the case where the particle volume of the magnetic powder is small. Solution to the problem

[0009] The above object is achieved by a tape-shaped magnetic recording medium according to claim 1 and by a tape cassette according to claim 18. The present disclosure provides a tape-shaped magnetic recording medium comprising: a base; and a magnetic layer provided on the base and containing a magnetic powder, wherein an average particle volume V of the magnetic powder 2000 nm 3 or less, an average thickness of the magnetic recording medium is 5.3 µm or less, a thermal stability K u V act / k B T of the magnetic recording medium is 60 or more and a ratio Hrp / Hc1 of a residual coercive force Hrp of the magnetic recording medium, measured using a pulsed magnetic field, to a coercive force Hc1 of the magnetic recording medium in the perpendicular direction is 2.10 or less.

[0010] The average particle volume V of the magnetic powder can be 1800 nm 3 or less.

[0011] The average particle volume V of the magnetic powder can be 1,600 nm 3 or less.

[0012] The thermal stability K u V act / k B T can be 63 or more.

[0013] D The thermal stability K u V act / k B T can be 65 or more.

[0014] The Hrp / Hc1 ratio may be 2.05 or less.

[0015] The Hrp / Hc1 ratio may be 2.00 or less.

[0016] The magnetic powder may contain hexagonal ferrite.

[0017] The hexagonal ferrite can contain Ba and / or Sr.

[0018] A signal attenuation amount SD of the magnetic recording medium 100 seconds after recording can satisfy the following relationship: - 0.30 dB ≤ SD.

[0019] The signal attenuation amount SD of the magnetic recording medium 100 seconds after recording can satisfy the following relationship: - 0.25 dB ≤ SD.

[0020] A thickness t m of the magnetic layer can satisfy the following relationship: 30 nm ≤ t m ≤ 90 nm.

[0021] The coercive force Hc1 can be 500 Oe or more.

[0022] An average thickness of the base can be 4.2 µm or less.

[0023] An underlayer may be provided between the magnetic layer and the base, and an average thickness of the underlayer can be 2.0 µm or less.

[0024] Of two surfaces of the base, a back layer may be provided on a surface opposite to a surface on which the magnetic layer is provided, and An average thickness of the back layer can be 0.6 µm or less.

[0025] An average particle size of the magnetic powder can be 50 nm or less.

[0026] The present disclosure also provides a tape cartridge comprising: the magnetic recording medium; a communication unit that communicates with a recording / reproducing device; a storage unit; and a control unit that stores in the storage unit information received from the recording / reproducing device via the communication unit, and reads the information from the storage unit and transmits the read information to the recording / reproducing device via the communication unit in response to a request from the recording / reproducing device, wherein the information includes adjustment information for adjusting the tension applied to the magnetic recording medium in the longitudinal direction. Brief description of the drawings [ Fig. 1] Fig. Figure 1 is a diagram showing an example of a magnetization curve and a residual magnetization curve. [ Fig. 2] Fig. 2 is a cross-sectional view of a magnetic recording medium according to an embodiment of the present disclosure. [ Fig. 3] Part A of Fig. Figure 3 is a schematic diagram showing the structure of a data band and a servo band. Part B of Fig. 3 is an enlarged view of the data band. [ Fig. 4] Fig. Figure 4 is an example of a TEM photograph of a magnetic layer. [ Fig. 5] Fig. Figure 5 is a cross-sectional view showing a configuration of magnetic particles. [ Fig. 6] Fig. 6 is a cross-sectional view showing a configuration of magnetic particles in a modified example. [ Fig. 7] Fig. Figure 7 is a graph showing an example of an MH loop. [ Fig. 8] Fig. Figure 8 is an example of a residual magnetization curve. [ Fig. 9] Fig. 9 is a schematic diagram of a recording / reproducing device. [ Fig. 10] Fig. 10 is an exploded perspective view showing an example of a configuration of a cassette. [ Fig. 11] Fig. 11 is a block diagram showing an example of a configuration of a cassette memory. [ Fig. 12] Fig. 12 is a schematic diagram showing a cross section of a magnetic recording medium according to a modified example. [ Fig. 13] Part A of Fig. Figure 13 shows an MFM image in the case where a data signal with a wavelength λ is recorded. Part B of Fig. Figure 13 shows an MFM image in the case where a data signal is recorded with the shortest recording wavelength L'. Mode(s) of carrying out the invention

[0027] An advantageous embodiment for carrying out the present disclosure will be described below. Note that the embodiment described below shows a typical embodiment of the present disclosure, and the scope of the present disclosure is not limited to these embodiments only.

[0028] The present invention will be described in the following order. 1. Description of the present disclosure 2. Embodiment (Example of a coating-type magnetic recording medium) (1) Configuration of the magnetic recording medium (2) Method for producing the magnetic recording medium (3) Recording / playback device (4) Cassette (5) Effects (6) Modified example 3. Example 1. Description of the present disclosure

[0029] A magnetic recording medium according to the present disclosure comprises: a magnetic layer containing a magnetic powder having a certain particle volume, an average thickness and a thermal stability K u V act / k B T are within certain numerical ranges, and a ratio Hrp / Hc1 of a residual coercive force Hrp of the magnetic recording medium, measured using a pulsed magnetic field, to a coercive force Hc1 of the magnetic recording medium in the perpendicular direction is within a certain numerical range. As a result, the magnetic recording medium according to the present disclosure has excellent preservation stability even though the particle volume of the magnetic powder is small. In addition, the magnetic recording medium according to the present disclosure has excellent electromagnetic conversion properties. The thermal stability Ku V act / k B T and the remaining coercivity Hrp are described in detail below.

[0030] The smaller the particle volume of the magnetic powder contained in the magnetic recording medium, the higher the recording density and the better the electromagnetic conversion characteristics. However, if the particle volume is smaller, the magnetization recorded in the magnetic recording medium (especially the magnetic layer) is likely to be lost due to thermal energy, which may lead to attenuation of the data signal. Thus, if the particle volume of the magnetic powder contained in the magnetic recording medium becomes smaller, the stability of the magnetic recording medium to heat (also called thermal stability) may be reduced, and the preservation stability of the magnetic recording medium may be reduced. Furthermore, if thermal stability is to be maintained, it becomes difficult to easily rewrite information.Although reducing the particle volume of the magnetic powder results in improved recording density and improved electromagnetic conversion properties, it leads to a reduction in preservation stability and, in some cases, also makes it difficult to rewrite information.

[0031] The relationship between the thermal stability and the coercive force of the magnetic recording medium can be expressed by the Bean equation shown below. (Math. 1)

[0032] In the equation, V act = the activation volume of the magnetic powder contained in the magnetic recording medium, H c = the coercive force, K u = the magnetocrystalline anisotropy, M = the magnetization volume, k B = the Boltzmann constant and T = the temperature.

[0033] K u V act / k BT, which consists of parameters included in this equation, is known as the index value of thermal stability. The higher the value, the higher the thermal stability. As can be seen from the thermal stability K u V act / k B As can be seen, the miniaturization of magnetic powder, that is, the reduction of the particle volume of the magnetic powder, leads to a reduction in thermal stability. The reduction in thermal stability leads to a reduction in the preservation stability of the magnetic recording medium.

[0034] This is particularly problematic when the magnetic recording medium is preserved for a longer period of time.

[0035] The magnetic recording medium according to the present disclosure has a thermal stability K u V act / k BT of 60 or more, preferably 63 or more, more preferably 65 or more, and even more preferably 70 or more. The magnetic recording medium according to the present disclosure has excellent thermal stability because it has a thermal stability K u V act / k B T within the above-mentioned numerical range, and is therefore excellent in preservation stability and also excellent in long-term preservation stability. Furthermore, the magnetic recording medium is also superior from the perspective of output signals.

[0036] Furthermore, the residual coercive force Hrp, particularly the ratio Hrp / Hc1 of the residual coercive force Hrp to the coercive force Hc1 of the magnetic recording medium in the perpendicular direction, also contributes to improving the preservation stability of the magnetic recording medium having a small average particle volume of the magnetic powder.

[0037] The remaining coercive force Hrp is given below with reference to Fig. 1 described.

[0038] The coercive force Hc1 in the perpendicular direction is an index that has been used in the past. To measure it, for example, an MH loop (magnetization curve) is generated based on the measurement result by a magnetometer. An example of the MH loop is shown in Fig. 1 shown.

[0039] As it is in Fig. As shown in Figure 1, the magnetic field at a position where the MH loop intersects the X-axis (magnetic field) is the coercive force Hc1. The field sweep rate used for this measurement is slow.

[0040] Unlike the measurement of the coercive force Hc1, the residual coercive force Hrp is measured using a pulsed magnetic field. That is, the measurement is performed using a fast field sweep rate. During the measurement, a magnetization curve is generated based on the magnetization volume obtained using the pulsed magnetic field. The magnetization curve is called the residual magnetization curve. An example of the residual magnetization curve is also shown in Fig. 1 shown.

[0041] The magnetic field at a position where the residual magnetization curve intersects the X-axis (magnetic field) is in Fig. 1 is given by “Hrp” and the magnetic field is a residual coercive force.

[0042] The inventors of the present invention have found that the thermal stability of the magnetic recording medium is improved when the difference between the coercive force Hc1 and the remaining coercive force Hrp is small, particularly when the ratio Hrp / Hc1 between the remaining coercive force Hrp and the coercive force Hc1 is within a certain numerical range.

[0043] Note that the residual coercivity Hrp is measured using a fast field sweep rate as described above. This fast field sweep rate is closer to the magnetic field applied by the magnetic recording medium during recording than the slow field sweep rate used when measuring the coercivity Hc1. From this point of view, the residual coercivity Hrp is also considered a valuable index.

[0044] The ratio Hrp / Hc1 of the residual coercive force Hrp to the coercive force Hc1 of the magnetic recording medium according to the present disclosure is 2.10 or less, preferably 2.05 or less, more preferably 2.00 or less, and even more preferably 1.95 or less, 1.90 or less, or 1.85 or less. When the above-mentioned ratio Hrp / Hc1 is within the above-mentioned numerical range, the magnetic recording medium according to the present disclosure has excellent preservation stability, making it possible, for example, to prevent signal attenuation during long-term preservation. Furthermore, when the ratio Hrp / Hc1 is within the above-mentioned numerical range, recording and reproduction can be performed stably even when the average particle volume of the magnetic powder contained in the magnetic recording medium is small.

[0045] Furthermore, an average particle volume V of the magnetic powder contained in the magnetic recording medium according to the present disclosure is 2000 nm 3 or less, preferably 1900 nm 3 or less, more preferably 1800 nm 3 or less and more preferably 1700 nm 3 or less. 1600 nm 3 or less or 1500 nm 3 or less. When the average particle volume is within the above numerical range, the electromagnetic conversion properties are improved.

[0046] Despite the very small average particle volume of the magnetic powder contained in the magnetic recording medium according to the present disclosure, the magnetic recording medium according to the present disclosure has excellent preservation stability as described above. Although it is difficult to achieve both electromagnetic conversion properties and preservation stability, both electromagnetic conversion properties and preservation stability can be improved by the present disclosure.

[0047] The signal attenuation amount SD 100 seconds after recording by the magnetic recording medium according to the present disclosure satisfies the following relationship: preferably -0.30 dB ≤ SD, more preferably -0.25 dB ≤ SD, and even more preferably -0.20 dB ≤ SD, -0.15 dB ≤ SD, or -0.10 dB ≤ SD. The signal attenuation amount SD 100 seconds after data is recorded by the magnetic recording medium according to the present disclosure can be low as described above. Therefore, the magnetic recording medium according to the present disclosure is excellent in data preservation stability and also in data preservation stability over a long period of time. The method for measuring the signal attenuation amount SD will be described below.It can be seen that the signal attenuation amount SD is an index of long-term preservation stability since it is extrapolated in logarithmic plots when calculating the signal attenuation as described in this specification.

[0048] For example, the signal attenuation amount SD 100 seconds after recording by the magnetic recording medium according to the present disclosure may satisfy the relationship SD ≤ 0.

[0049] An average thickness t T of the magnetic recording medium according to the present disclosure is preferably 5.3 µm or less, more preferably 5.2 µm or less, and even more preferably 5.1 µm or less, 5.0 µm or less, 4.8 µm or less, or 4.6 µm or less. The magnetic recording medium according to the present disclosure can thus be thin in overall thickness.

[0050] By reducing the overall thickness of the magnetic recording medium according to the present disclosure in this way, for example, the length of the tape to be wound into a magnetic recording cartridge can be extended, thereby increasing the recording capacity per magnetic recording cartridge. In other words, the present disclosure can improve the recording capacity in addition to improving the electromagnetic conversion characteristics and preservation stability.

[0051] The width of the magnetic recording medium according to the present disclosure may be, for example, 5 mm to 30 mm, in particular 7 mm to 25 mm, in particular 10 mm to 20 mm, and in particular 11 mm to 19 mm. The length of the tape magnetic recording medium according to the present disclosure may be, for example, 500 m to 1500 m. For example, the width of the tape according to the LTO8 standard is 12.65 mm and the length of the tape is 960 m.

[0052] The magnetic recording medium according to the present disclosure has a tape shape and may, for example, be an elongated magnetic recording tape. The tape-like magnetic recording medium according to the present disclosure may, for example, be accommodated in a magnetic recording cartridge. Specifically, it may be accommodated in the cartridge by being wound onto a reel in the magnetic recording cartridge.

[0053] In one advantageous embodiment of the present disclosure, the magnetic recording medium according to the present disclosure may include a magnetic layer, an underlayer, a base (also referred to as a base layer), and a back layer. These four layers may be stacked in this order. The magnetic recording medium according to the present disclosure may include other layers in addition to these layers. The other layers may be appropriately selected depending on the type of magnetic recording medium. The magnetic recording medium according to the present disclosure may be, for example, a coating-type magnetic recording medium.

[0054] The coating type magnetic recording medium is described in more detail in Section 2 below. 2. Embodiment (Example of a coating type magnetic recording medium)(1) Configuration of the magnetic recording medium

[0055] First, a configuration of a magnetic recording medium 10 according to an embodiment will be described with reference to Fig. 2. The magnetic recording medium 10 includes an elongated base 11, an underlayer 12 provided on one major surface of the base 11, a magnetic layer 13 provided on the underlayer 12, and a back layer 14 provided on the other major surface of the base 11. Note that the underlayer 12 and the back layer 14 are provided as needed and are not mandatory.

[0056] The magnetic recording medium 10 has a long, tape-like shape and is caused to move in the longitudinal direction during recording and playback. Note that the surface of the magnetic layer 13 is the surface on which the magnetic head moves. The magnetic recording medium 10 is preferably used in a recording / reproducing device having a ring-type head as the recording head. Note that in this specification, the "perpendicular direction" means a direction perpendicular to the surface of the magnetic recording medium 10 (the thickness direction of the magnetic recording medium 10), and the "longitudinal direction" means a longitudinal direction (travel direction) of the magnetic recording medium 10. (Base)

[0057] The base 11 is a non-magnetic support supporting the undercoat layer 12 and the magnetic layer 13. The base 11 has a long film-like shape. The average thickness of the base 11 is preferably 4.2 µm or less, more preferably 3.8 µm or less, and still more preferably 3.4 µm or less. When the average thickness of the base 11 is 4.2 µm or less, the recording capacity in a data cartridge can be increased compared to a typical magnetic recording medium. The average thickness of the base 11 is preferably 3 µm or more, and more preferably 3.2 µm or more. When the average thickness of the base 11 is 3 µm or more, a decrease in the intensity of the base 11 can be suppressed.

[0058] The average thickness of the base 11 is obtained as follows. First, the magnetic recording medium 10 is prepared with a width of 1 / 2 inch and cut into a length of 250 mm to prepare a sample. Then, layers other than the base 11 of the sample (i.e., the underlayer 12, the magnetic layer 13, and the back layer 14) are removed with a solvent such as MEK (methyl ethyl ketone) and diluted hydrochloric acid. Next, using a laser holometry instrument (LGH-110C) manufactured by Mitutoyo Corporation as the measuring device, the thickness of the sample (base 11) is measured at five or more points, and the measured values are simply averaged (arithmetically averaged) to calculate the average thickness of the base 11. Note that the measurement positions are randomly selected from the sample.

[0059] The base 11 contains, for example, polyesters, polyolefins, cellulose derivatives, vinyl resins, and / or various polymer resins. In the case where the base 11 contains two or more of the above-mentioned materials, the two or more materials may be blended, copolymerized, or stacked.

[0060] The polyesters include, for example, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylenedimethylene terephthalate), PEB (polyethylene p-oxybenzoate) and / or polyethylene bisphenoxycarboxylate.

[0061] Polyolefins include, for example, PE (polyethylene) and / or PP (polypropylene). Cellulose derivatives include, for example, cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and / or CAP (cellulose acetate propionate). Vinyl resins include, for example, PVC (polyvinyl chloride) and / or PVDC (polyvinylidene chloride).

[0062] The various polymer resins include, for example, PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, e.g. Zylon (registered trademark)), polyether, PEK (polyether ketone), polyether ester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate) and / or PU (polyurethane).

[0063] The base 11 contains, for example, a polyester as the main component. The polyester may be, for example, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylenedimethylene terephthalate), PEB (polyethylene p-oxybenzoate), or polyethylene bisphenoxycarboxylate, or a mixture of two or more thereof. In this specification, the "main component" means the component with the highest content ratio among the components constituting the base. For example, polyester as the main component of the base 11 may mean that the content of the polyester in the base 11 based on the mass of the base layer 11 is, for example, 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, 90 mass% or more, 95 mass% or more, or 98 mass% or more, or that the base layer 11 consists only of polyester.

[0064] In this embodiment, the base 11 may contain, in addition to the polyester, a resin other than polyester described below.

[0065] According to an advantageous embodiment of the present technology, the base 11 may be formed of PET or PEN. (Magnetic layer)

[0066] The magnetic layer 13 is a recording layer for recording signals. The magnetic layer 13 contains, for example, a magnetic powder and a binder. The magnetic layer 13 may further contain at least one additive selected from a lubricant, an antistatic agent, an abrasive, a hardening agent, a rust inhibitor, non-magnetic reinforcing particles, and the like, as needed.

[0067] It is preferable that the magnetic layer 13 contains in advance a plurality of servo bands SB and a plurality of data bands DB as shown in Part A of Fig. 3. The plurality of servo bands SB are provided at equal intervals in the width direction of the magnetic recording medium 10. The data band DB is provided between adjacent servo bands SB. A servo signal for controlling the tracking of the magnetic head is pre-written into the servo band SB. User data is recorded on the data band DB.

[0068] From the point of view of ensuring a high recording capacity, a ratio R S (=(S SB / S)×100) of a total area S SB of the servo bands SB to an area S of the surface of the magnetic layer 13 is preferably 4.0% or less, more preferably 3.0% or less, and even more preferably 2.0% or less. From the viewpoint of ensuring five or more servo tracks, the ratio R S of the total area S SBof the servo bands SB to the area S of the surface of the magnetic layer 13 is preferably 0.8% or more.

[0069] The ratio R S of the total area S SB of the servo bands SB to the area S of the entire surface of the magnetic layer 13 is obtained as follows. For example, the magnetic recording medium 10 is developed using a ferric colloid developer (SigMarker Q, manufactured by Sigma Hi Chemical Inc.), and the developed magnetic recording medium 10 is then observed under an optical microscope to determine a servo band width W SB and the number of servo bands SB. Next, the ratio R S obtained from the following formula. Ratio RS [%] = (((Servo bandwidth WSB) × (number of servo bands)) / (width of the magnetic recording medium 10)) × 100

[0070] The number of servo bands SB is preferably 5 or more, more preferably 5+4n (however, n is a positive integer) or more, and even more preferably 9+4n or more. When the number of servo bands SB is 5 or more, the effect on the servo signal due to the dimensional change of the magnetic recording medium 10 in the width direction can be suppressed, and stable recording / reproducing characteristics with less deviation can be ensured. The number of servo bands SB is not particularly limited, but is, for example, 33 or less.

[0071] The number of servo bands SB can be checked as follows. First, the surface of the magnetic layer 13 is observed using a magnetic force microscope (MFM) to obtain an MFM image. Next, the number of servo bands SB is counted using the MFM image.

[0072] The servo bandwidth W SBis preferably 95 µm or less, more preferably 60 µm or less, and even more preferably 30 µm or less from the viewpoint of ensuring high recording capacity. The servo bandwidth W SB is preferably 10 µm or more. The production of a recording head that transmits the servo signal with a servo bandwidth W SB of less than 10 µm is a challenge.

[0073] The servo bandwidth W SB is obtained as follows. First, the surface of the magnetic layer 13 is observed using a magnetic force microscope (MFM) to obtain an MFM image. Next, the W SB the servo bandwidth using the MFM image.

[0074] As described in Part B of Fig. 3, the magnetic layer 13 is configured to form a plurality of data tracks Tk on the data tape DB. From the viewpoint of ensuring high recording capacity, a data track width W is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.0 μm or less. The data track width W is preferably 0.02 μm or more.

[0075] The data track width W is obtained as follows. For example, data recording patterns of data tape portions of the magnetic layer 13 in which data is recorded are observed on the entire surface using a magnetic force microscope (MFM) to obtain an MFM image. The Dimension 3100 manufactured by Digital Instruments and its analysis software are used as the MFM. The measurement area of the MFM image is 10 µm × 10 µm, and the 10 µm × 10 µm measurement area is divided into 512 × 512 (= 262144) measurement points. The MFM measurement is performed on three 10 µm × 10 µm measurement areas at different locations, that is, three MFM images are obtained. From the three obtained MFM images, the track widths at 10 locations are measured using the analysis software connected to the Dimension 3100, and the average value (which is a simple average) is obtained. The obtained average value is the data track width W.It should be noted that the measurement conditions of MFM are as follows: sweep rate: 1 Hz, used chip: MFMR-20, stroke height: 20 nm and correction: flattening order 3.

[0076] The magnetic layer 13 is designed to be able to record data so that a minimum value L of the magnetization reversal pitch and the data track width W satisfy the following relationship: preferably W / L ≤ 200, more preferably W / L ≤ 60, even more preferably W / L ≤ 45, and particularly preferably W / L ≤ 30.

[0077] When the minimum value L of the magnetization reversal pitch is a constant value, and the minimum value L of the magnetization reversal pitch and the track width W satisfy the following relationship: W / L> 200 (that is, when the track width W is large), since the track recording density does not increase, there is a possibility that the recording capacity cannot be sufficiently ensured. Furthermore, when the track width W is a constant value, and the minimum value L of the magnetization reversal pitch and the track width W satisfy the following relationship: W / L> 200 (that is, when the minimum value L of the magnetization reversal pitch is small), there is a possibility that the SNR will deteriorate significantly due to the effect of pitch loss even though the bit length is reduced and the line recording density is increased.Therefore, in order to suppress the deterioration of SNR while ensuring the recording capacity, it is preferable that W / L be in the range of W / L ≤ 60 as described above. However, W / L is not limited to the above range and may satisfy the following relationship: W / L ≤ 23 or W / L ≤ 13. The lower limit of W / L is not particularly limited, but is, for example, 1 ≤ W / L.

[0078] From the viewpoint of ensuring high recording capacity, the magnetic layer 13 is designed to be able to record data such that the minimum value L of the magnetization reversal distance is still preferably 55 nm or less, more preferably 53 nm or less, even more preferably 52 nm or less, 50 nm or less, 48 nm or less, or 44 nm, and particularly preferably 40 nm or less. The lower limit of the minimum value L of the magnetization reversal distance is preferably 20 nm or more in view of the magnetic particle size. The minimum value L of the magnetization reversal distance is taken into account by the magnetic particle size. The minimum value L of the

[0079] Magnetization reversal pitch is obtained as follows. For example, data recording patterns of data tape portions of the magnetic layer 13 in which data is recorded are observed on the entire surface using a magnetic force microscope (MFM) to obtain an MFM image. The Dimension 3100 manufactured by Digital Instruments and its analysis software are used as the MFM. The measurement area of the MFM image is 2 μm × 2 μm, and the 2 μm × 2 μm measurement area is divided into 512 × 512 (= 262144) measurement points. The MFM measurement is performed on three 2 μ × 2 μm measurement areas at different locations, that is, three MFM images are obtained. From the two-dimensional uneven diagram of the recording pattern of the obtained MFM image, 50 bit-to-bit pitches are measured. The bit-to-bit distances are measured using the analysis software included with Dimension 3100.The value that approximately becomes the greatest common factor of the 50 measured bit-to-bit distances is defined as the minimum value L of the magnetization reversal distance. Note that the measurement conditions are as follows: sweep rate: 1 Hz, chip used: MFMR-20, lift height: 20 nm, and correction: flattening order 3.

[0080] An average thickness t m of the magnetic layer 13 is preferably 90 nm or less, more preferably 80 nm or less, more preferably 70 nm or less, and even more preferably 50 nm or less. When the average thickness of the magnetic layer 13 is 90 nm or less, since the magnetization can be recorded uniformly in the thickness direction of the magnetic layer 13 when a ring-type head is used as the recording head, the electromagnetic conversion characteristics (e.g., SNR (signal-to-noise ratio)) can be improved.

[0081] The average thickness t m The average thickness of the magnetic layer 13 is preferably 30 nm or more, and more preferably 35 nm or more. When the average thickness of the magnetic layer 13 is 30 nm or more, the output can be ensured in the case where an MR type head is used as the reproducing head, so that the electromagnetic conversion characteristics (e.g., SNR) can be improved.

[0082] The numerical range of the average thickness of the magnetic layer 13 can be defined by one of the above-mentioned upper limit values and one of the above-mentioned lower limit values and can satisfy the following relationship: preferably 30 nm ≤ t m ≤ 90 nm, 35 nm ≤ t m ≤ 80 nm or 35 nm ≤ t m ≤ 70 nm.

[0083] The average thickness of the magnetic layer 13 is obtained, for example, as follows.

[0084] The magnetic recording medium 10 is processed by a focused ion beam (FIB) method or the like to obtain a layer. When using the FIB method, a carbon film and a tungsten thin film as a protective film are formed as preprocessing for observing a TEM image of a cross section to be described below. The carbon film is formed on the magnetic layer-side surface and the back layer-side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer-side surface by an evaporation method or a sputtering method. Cutting is performed along the length direction (longitudinal direction) of the magnetic recording medium 10.That is, the cutting forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10.

[0085] The above-mentioned cross-section of the obtained cut sample is observed with a transmission electron microscope (TEM) under the following conditions to obtain a TEM image. Note that depending on the device type, the magnification and acceleration voltage can be adjusted accordingly. Device: TEM (H9000NAR, manufactured by Hitachi Ltd.) Acceleration voltage: 300 kV Magnification: 100,000x

[0086] Next, the obtained TEM image is used to measure the thickness of the magnetic layer 13 at at least 10 positions in the longitudinal direction of the magnetic recording medium 10. The obtained measurement values are simply averaged (arithmetically averaged), and the obtained average value is taken as the average thickness [nm] of the magnetic layer 13. Note that the positions where the measurement is performed are randomly selected from the test pieces. (Magnetic powder)

[0087] Examples of magnetic particles constituting the magnetic powder contained in the magnetic layer 13 include, but are not limited to, hexagonal ferrite, epsilon-type iron oxide (ε-iron oxide), Co-containing spinel ferrite, gamma hematite, magnetite, dichromium dioxide, cobalt-deposited iron oxide, and metal. The magnetic powder may be one of these or a combination of two or more thereof. It is preferable that the magnetic powder may contain hexagonal ferrite, ε-iron oxide, or Co-containing spinel ferrite. More preferably, the magnetic powder is hexagonal ferrite. Hexagonal ferrite may more preferably contain Ba and / or Sr. The ε-iron oxide may more preferably contain Al and / or Ga. These magnetic particles can be appropriately selected by those skilled in the art based on factors such as the method for manufacturing the magnetic layer 13, the standard of the tape, and the function of the tape.

[0088] The shape of the magnetic particles depends on the crystal structure of the magnetic particles. For example, barium ferrite (BaFe) and strontium ferrite can have a hexagonal plate shape. ε-iron oxide can be spherical. Cobalt ferrite can be cubic. The metal can be spindle-shaped. These magnetic particles are aligned during the manufacture of the magnetic recording medium 10.

[0089] The average particle size of the magnetic powder may preferably be 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less, 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm or less. The average particle size may, for example, be 10 nm or more, and preferably 12 nm or more.

[0090] For example, the average aspect ratio of the magnetic powder may be 1.0 or more and 3.0 or less, and may be 1.0 or more and 2.9 or less. (Embodiment in which the magnetic powder contains hexagonal ferrite)

[0091] According to an advantageous embodiment of the present disclosure, the magnetic powder contains hexagonal ferrite, in particular a powder of nanoparticles containing hexagonal ferrite (hereinafter referred to as "hexagonal ferrite particles"). Hexagonal ferrite is preferably hexagonal ferrite having an M-type structure. Hexagonal ferrite has, for example, a hexagonal plate shape or a substantially hexagonal plate shape. Hexagonal ferrite may preferably contain Ba, Sr, Pb, and / or Ca, and more preferably Ba, Sr, and / or Ca. In particular, hexagonal ferrite may be, for example, one selected from the group consisting of barium ferrite, strontium ferrite, and calcium ferrite, or a combination of two or more thereof, and is particularly preferably barium ferrite or strontium ferrite. Barium ferrite may further contain Sr, Pb, and / or Ca in addition to Ba. Strontium ferrite may further contain Ba, Pb, and / or Ca in addition to Sr.

[0092] In particular, hexagonal ferrite may have an average composition represented by the general formula MFe 12 O 19 Here, M is, for example, at least one metal selected from Ba, Sr, Pb, or Ca, and preferably at least one metal selected from Ba or Sr. M may be a combination of Ba and one or more metals selected from the group consisting of Sr, Pb, and Ca. Further, M may be a combination of Sr and one or more metals selected from the group consisting of Ba, Pb, and Ca. In the above-mentioned general formula, some Fe may be replaced by other metal elements.

[0093] In the case where the magnetic powder contains a powder of hexagonal ferrite particles, the average particle size of the magnetic powder may preferably be 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less, 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm or less. The average particle size may, for example, be 10 nm or more, preferably 12 nm or more, and more preferably 15 nm or more. For example, the average particle size of the magnetic powder may be 10 nm or more and 50 nm or less, 10 nm or more and 40 nm or less, 12 nm or more and 30 nm or less, 12 nm or more and 25 nm or less, or 15 nm or more and 22 nm or less. In the case where the average particle size of the magnetic powder is less than or equal to the above-mentioned upper limit (e.g.50 nm or less, particularly 30 nm or less), preferable electromagnetic conversion characteristics (e.g., SNR) can be obtained in the high-density magnetic recording medium 10. In the case where the average particle size of the magnetic powder is not smaller than the above-mentioned lower limit (e.g., 10 nm or more, preferably 12 nm or more), the dispersibility of the magnetic powder is further improved, and more excellent electromagnetic conversion characteristics (e.g., SNR) can be obtained.

[0094] In the case where the magnetic powder contains hexagonal ferrite particle powder, the average aspect ratio of the magnetic powder may preferably be 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.9 or less, and even more preferably 2.0 or more and 2.9 or less. When the average aspect ratio of the magnetic powder is within the above-mentioned numerical range, it is possible to suppress the aggregation of the magnetic powder and suppress the resistance exerted on the magnetic powder at the time the magnetic powder is perpendicularly aligned in the process of forming the magnetic layer 13. This can lead to an improvement in the perpendicular alignment of the magnetic powder.

[0095] In the case where the magnetic powder contains a powder of hexagonal ferrite particles, the average particle size and the average aspect ratio of the magnetic powder are obtained as follows.

[0096] First, the magnetic recording medium 10 to be measured is processed by the focused ion beam (FIB) method or the like to obtain a section. When using the FIB method, a carbon film and a tungsten thin film as a protective film are formed as preprocessing for observing a TEM image of a cross section to be described below. The carbon film is formed on the magnetic layer-side surface and the back layer-side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer-side surface by an evaporation method or a sputtering method. The cutting is performed along the length direction (longitudinal direction) of the magnetic recording medium 10.That is, the cutting forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10.

[0097] Using a transmission electron microscopy (H-9500, manufactured by Hitachi High-Tech Corporation), the above-mentioned cross section of the obtained section sample is observed at an accelerating voltage of 200 kV and a total magnification of 500,000 so that the entire magnetic layer 13 is included with respect to the thickness direction of the magnetic layer 13, and a TEM photograph is taken.

[0098] Next, 50 particles whose side faces are oriented toward the observation area and whose thickness can be clearly observed are selected from the obtained TEM photograph. For example, Fig. 4 an example of the TEM photo. In Fig. 4, for example, particles indicated by a and d are selected because their thickness can be clearly observed. For each of the 50 selected particles, a maximum plate thickness DA is measured. The maximum plate thicknesses DA thus obtained are simply averaged (arithmetically averaged) to obtain an average maximum plate thickness DA. ave to obtain.

[0099] Subsequently, a plate diameter DB of each of the magnetic powders is measured. To measure the plate diameter DB of the particles, 50 particles whose plate diameter can be clearly observed are selected from the obtained TEM photograph. For example, in Fig. Four particles were selected, indicated by b and c, because their plate diameters could be clearly observed. The plate diameter DB of each of the 50 selected particles was measured. The resulting plate diameters DB were simply averaged (arithmetically averaged) to obtain an average plate diameter DB. ave The average plate diameter DB ave is the average particle size.

[0100] Then an average aspect ratio (DB ave / DA ave ) of the particles from the average maximum plate thickness DA ave and the average plate diameter DB ave receive.

[0101] In the case where the magnetic powder contains a powder of hexagonal ferrite particles, the average particle volume of the magnetic powder is preferably 2000 nm 3 or less, preferably 1900 nm 3or less, more preferably 1800 nm 3 or less and more preferably 1700 nm 3 or less, 1600 nm 3 or less or 1500 nm 3 or less. The average particle volume of the magnetic powder is preferably 500 nm 3 or more and preferably 700 nm 3 or more.

[0102] In the case where the average particle volume of the magnetic powder is less than or equal to the above-mentioned upper limit (e.g., 2000 nm3 or less), preferable electromagnetic conversion characteristics (e.g., SNR) can be achieved in the high-density magnetic recording medium 10. In the case where the average particle volume of the magnetic powder is greater than or equal to the above-mentioned lower limit (e.g., 500 nm 3or more), the dispersibility of the magnetic powder is further improved and the more excellent electromagnetic conversion properties (e.g., SNR) can be achieved.

[0103] The average particle volume of the magnetic powder is obtained as follows. First, as described in the above-mentioned method for calculating the average particle size of the magnetic powder, the average maximum plate thickness DA ave and the average plate diameter DB ave Next, the average particle volume V of the magnetic powder is obtained by the following formula. [Math. 2]

[0104] According to a particularly preferred embodiment of the present disclosure, the magnetic powder may be a barium ferrite magnetic powder or a strontium ferrite magnetic powder, and may more preferably be a barium ferrite magnetic powder. The magnetic powder contains magnetic iron oxide particles having barium ferrite as the main phase (hereinafter referred to as "barium ferrite particles"). The barium ferrite magnetic powder is highly reliable in data recording; for example, the coercive force of the barium ferrite magnetic powder does not drop even in high-temperature and high-humidity environments. From this point of view, the barium ferrite magnetic powder is preferable as the above-mentioned magnetic powder.

[0105] The average particle size of the barium ferrite magnetic powder is 50 nm or less, more preferably 10 nm or more and 40 nm or less, and even more preferably 12 nm or more and 25 nm or less.

[0106] In the case where the magnetic layer 13 contains barium ferrite magnetic powder as the magnetic powder, the average thickness t m [nm] of the magnetic layer 13 is preferably 90 nm or less, and more preferably 80 nm or less. For example, the average thickness t m of the magnetic layer 13 satisfy the following relationship: 35 nm ≤ t m ≤ 90 nm.

[0107] In addition, the coercive force Hc1 measured in the thickness direction (vertical direction) of the magnetic recording medium 10 is preferably 2010 [Oe] or more and 3520 [Oe] or less, more preferably 2070 [Oe] or more and 3460 [Oe] or less, and still more preferably 2140 [Oe] or more and 3390 [Oe] or less. (Embodiment in which the magnetic powder contains ε-iron oxide)

[0108] According to another preferred embodiment of the present disclosure, the above-mentioned magnetic powder may preferably comprise a powder of nanoparticles containing ε-iron oxide (hereinafter referred to as "ε-iron oxide particles"). The ε-iron oxide particles can achieve a high coercive force even when the ε-iron oxide particles are fine particles. The ε-iron oxide contained in the ε-iron oxide particles is preferably crystal-oriented, preferably in the thickness direction (perpendicular direction) of the magnetic recording medium 10.

[0109] The ε-iron oxide particles each have a spherical or substantially spherical shape, or each have a cubic or substantially cubic shape. Since the ε-iron oxide particles have the above-mentioned shapes, when ε-iron oxide particles are used as magnetic particles, the contact area between the particles in the thickness direction of the medium can be reduced and the aggregation of the particles can be suppressed compared to the case of using hexagonal plate-shaped barium ferrite particles as magnetic particles. Therefore, it is possible to increase the dispersibility of the magnetic powder and achieve a more favorable SNR (signal-to-noise ratio).

[0110] The ε-iron oxide particles may each have a core-shell structure. Specifically, the ε-iron oxide particles each have a core portion 21 and a shell portion 22 with a two-layer structure provided around the core portion 21, as shown in Fig. 5. The shell portion 22 having the two-layer structure includes a first shell portion 22a provided on the core portion 21 and a second shell portion 22b provided on the first shell portion 22a.

[0111] The core portion 21 contains ε-iron oxide. The ε-iron oxide contained in the core portion 21 preferably has an ε-Fe2O3 crystal as the main phase, and more preferably a single phase of ε-Fe2O3.

[0112] The first shell portion 22a covers at least a part of the circumference of the core portion 21. In particular, the first shell portion 22a may partially cover the circumference of the core portion 21 or cover the entire circumference of the core portion 21.

[0113] From the viewpoint of achieving sufficient exchange coupling between the core portion 21 and the first shell portion 22a and improving the magnetic properties, covering the entire surface of the core portion 21 is preferable.

[0114] The first shell portion 22a is a so-called soft magnetic layer and may contain a soft magnetic material such as α-Fe, a Ni-Fe alloy, and a Fe-Si-Al alloy. α-Fe can be obtained by reducing the ε-iron oxide contained in the core portion 21.

[0115] The second shell portion 22b is an oxide coating film as an oxidation prevention layer. The second shell portion 22b may contain α-iron oxide, aluminum oxide, or silicon oxide. For example, α-iron oxide may contain at least one iron oxide selected from Fe3O4, Fe2O3, or FeO. In the case where the first shell portion 22a contains α-Fe (soft magnetic material), the α-iron oxide may be one obtained by oxidizing α-Fe contained in the first shell portion 22a.

[0116] When the ε-iron oxide particles each have the first shell portion 22a as described above, thermal stability can be ensured. This makes it possible to keep the coercive force Hc of the core portion 21 alone high and / or to adjust the coercive force Hc of the ε-iron oxide particles (core-shell particles) as a whole to the coercive force Hc suitable for recording. When the ε-iron oxide particles each have the second shell portion 22b as described above, deterioration of the properties of the ε-iron oxide particles due to rust or the like on the surfaces of the particles can be suppressed by exposing the ε-iron oxide particles to air during the process of manufacturing the magnetic recording medium 10 and before the process. Therefore, it is possible to suppress the characteristic deterioration of the magnetic recording medium 10.

[0117] The ε-iron oxide particles may have a shell portion 23 with a single layer structure as shown in Fig. 6. In this case, the shell portion 23 has the same configuration as the first shell portion 22a. However, from the viewpoint of suppressing the deterioration of the properties of the ε-iron oxide particles, it is more preferable that the ε-iron oxide particles each have the shell portion 22 having a two-layer structure.

[0118] The ε-iron oxide particles may contain an additive instead of a core-shell structure, or may contain an additive and simultaneously have a core-shell structure. In these cases, part of the Fe of the ε-iron oxide particles is replaced with additives. When the ε-iron oxide particles also contain an additive, the coercive force Hc of the entire ε-iron oxide particles can be adjusted to the coercive force Hc suitable for recording, so that the ease of recording can be improved. The additive is a metal element other than iron, preferably a trivalent metal element, and more preferably one or more types selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In).

[0119] In particular, the ε-iron oxide containing an additive is an ε-Fe2- x M xO3 crystal (where M represents a metal element other than iron, preferably a trivalent metal element, and more preferably one or more species selected from the group consisting of Al, Ga, and In. For example, x satisfies the following formula represented by 0 < x < 1.).

[0120] The average particle size (average maximum particle size) of the magnetic powder is preferably 22 nm or less, more preferably 8 nm or more and 22 nm or less, and even more preferably 12 nm or more and 22 nm or less. In the magnetic recording medium 10, the region half the recording wavelength is the actual magnetization region. Therefore, by setting the average particle size of the magnetic powder to half or less of the shortest recording wavelength, it is possible to achieve a preferable SNR. Therefore, when the average particle size of the magnetic powder is 22 nm or less, preferable electromagnetic conversion characteristics (e.g., SNR) can be achieved in the high-density magnetic recording medium 10 (e.g.,the magnetic recording medium 10, which is designed to record signals with the shortest recording wavelength of 44 nm or less). Meanwhile, in the case where the average particle size of the magnetic powder is 8 nm or more, the dispersibility of the powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be achieved.

[0121] The average aspect ratio of the magnetic powder is preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.9 or less, and even more preferably 1.0 or more and 2.5 or less. When the average aspect ratio of the magnetic powder is within the above-mentioned numerical range, the aggregation of the magnetic powder can be suppressed, and the resistance exerted on the magnetic powder at the time the magnetic powder is perpendicularly aligned in the process of forming the magnetic layer 13 can be suppressed. Therefore, the perpendicularity of the magnetic powder can be improved.

[0122] In the case where the magnetic powder contains ε-iron oxide particles, the average particle size and the average aspect ratio of the magnetic powder are obtained as follows.

[0123] First, the magnetic recording medium 10 to be measured is processed by the focused ion beam (FIB) method or the like to obtain a section. When using the FIB method, a carbon film and a tungsten thin film as a protective film are formed as preprocessing for observing a TEM image of a cross section to be described below. The carbon film is formed on the magnetic layer-side surface and the back layer-side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer-side surface by an evaporation method or a sputtering method. The cutting is performed along the length direction (longitudinal direction) of the magnetic recording medium 10.That is, the cutting forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10.

[0124] Using a transmission electron microscopy (H-9500, manufactured by Hitachi High-Tech Corporation), the above-mentioned cross section of the obtained section sample is observed at an accelerating voltage of 200 kV and a total magnification of 500,000 so that the entire magnetic layer 13 is included with respect to the thickness direction of the magnetic layer 13, and a TEM photograph is taken.

[0125] Next, 50 particles whose shapes can be clearly observed are selected from the obtained TEM photograph, and the major axis length DL and minor axis length DS of each particle are measured. Here, the major axis length DL represents the largest (so-called maximum Feret diameter) distance between two parallel lines drawn from all angles so that they touch the contour of the particle. Meanwhile, the minor axis length DS represents the largest length of the particles in the direction perpendicular to the major axis (DL) of the particles.

[0126] Subsequently, the measured major axis lengths DL of the 50 particles are simply averaged (arithmetically averaged) to obtain an average major axis length DL ave The average major axis length DL thus obtained aveis used as the average particle size of the magnetic powder. Furthermore, the measured minor axis lengths DS of the 50 particles are simply averaged (arithmetically averaged) to obtain an average minor axis length DS ave Then an average aspect ratio (DL ave / DS ave ) of the particles from the average major axis length DL ave and the average minor axis length DS ave receive.

[0127] The average particle volume of the magnetic powder is preferably 2000 nm 3 or less, preferably 1900 nm 3 or less, more preferably 1800 nm 3 or less, and more preferably 1700 or less, 1600 or less, or 1500 nm 3 or less. The average particle volume of the magnetic powder is preferably 500 nm 3 or more and preferably 700 nm 3 or more.

[0128] In the case where the average particle volume of the magnetic powder is less than or equal to the above upper limit (e.g. 2000 nm 3 or less), the magnetic recording medium 10 with high recording density can achieve preferable electromagnetic conversion characteristics (e.g., SNR). In the case where the average particle volume of the magnetic powder is greater than or equal to the above-mentioned lower limit (e.g., 500 nm 3 or more), the dispersibility of the magnetic powder is further improved and more excellent electromagnetic conversion properties (e.g., SNR) can be achieved.

[0129] In the case where the ε-iron oxide particles are spherical or substantially spherical, the average particle volume of the magnetic powder is obtained as follows. First, the average major axis length DL avein the same way as in the above-mentioned method for calculating the average particle size of the magnetic powder. Next, the average particle volume V of the magnetic powder is obtained by the following formula. V=(π / 6)×DLave3

[0130] In the case where the ε-iron oxide particles each have a cubic shape, the average particle volume of the magnetic powder is obtained as follows.

[0131] The magnetic recording medium 10 is processed by the focused ion beam (FIB) method or the like to obtain a section. When using the FIB method, a carbon film and a tungsten thin film as a protective film are formed as preprocessing for observing a TEM image of a cross section to be described below. The carbon film is formed on the magnetic layer-side surface and the back layer-side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer-side surface by an evaporation method or a sputtering method. The cutting is performed along the length direction (longitudinal direction) of the magnetic recording medium 10.That is, the cutting forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10.

[0132] Using a transmission electron microscope (H-9500, manufactured by Hitachi High-Tech Corporation), the above-mentioned cross-section of the obtained section sample was observed at an acceleration voltage of 200 kV and a total magnification of 500,000 so that the entire magnetic layer 13 was included with respect to the thickness direction of the magnetic layer 13, and a TEM photograph was taken. Note that depending on the device type, the magnification and acceleration voltage may be adjusted accordingly.

[0133] Next, 50 particles whose shapes can be clearly observed are selected from the obtained TEM photograph, and a side length DC of each particle is measured. Then, the measured side lengths DC of the 50 particles are simply averaged (arithmetically averaged) to obtain an average side length DC ave Next, the average side length DC ave used to calculate an average particle volume V ave (particle volume) of the magnetic powder from the following formula. Vave=DCave3

[0134] The coercive force Hc of the ε-iron oxide particles is preferably 2500 Oe or more, and more preferably 2800 Oe or more and 4200 Oe or less. (Embodiment in which the magnetic powder contains Co-containing spinel ferrite)

[0135] According to yet another advantageous embodiment of the present disclosure, the magnetic powder may comprise a powder of nanoparticles containing Co-containing spinel ferrite (hereinafter also referred to as "cobalt ferrite particles"). That is, the magnetic powder may be a cobalt ferrite magnetic powder. The cobalt ferrite particles advantageously have uniaxial crystal anisotropy. The cobalt ferrite magnetic particles each have, for example, a cubic shape or a substantially cubic shape. The Co-containing spinel ferrite may contain, in addition to Co, one or more species selected from the group consisting of Ni, Mn, Al, Cu, and Zn.

[0136] For example, cobalt ferrite has the average composition represented by the following formula (1). Co x M y Fe2O z (1)

[0137] (In formula (1), however, M represents, for example, one or more metals selected from the group consisting of Ni, Mn, Al, Cu, and Zn. X represents a value in the range 0.4 ≤ x ≤ 1.0. y represents a value in the range 0 ≤ y ≤ 0.3. However, x and y satisfy the following relationship: (x+y) ≤ 1.0. z represents a value in the range 3 ≤ z ≤ 4. Part of Fe can be replaced by other metal elements.)

[0138] The average particle size of the cobalt ferrite magnetic powder is preferably 25 nm or less, and more preferably 23 nm or less. The coercive force Hc of the cobalt ferrite magnetic powder is preferably 2500 Oe or more, and more preferably 2600 Oe or more and 3500 Oe or less.

[0139] In the case where the magnetic powder contains cobalt ferrite particle powder, the average particle size of the magnetic powder is preferably 25 nm or less, and more preferably 10 nm or more and 23 nm or less. When the average particle size of the magnetic powder is 25 nm or less, favorable electromagnetic conversion characteristics (e.g., SNR) can be achieved in the high-density magnetic recording medium 10. When the average particle size of the magnetic powder is 10 nm or more, the dispersibility of the magnetic powder is further improved, and more excellent electromagnetic conversion characteristics (e.g., SNR) can be obtained.In the case where the magnetic powder contains a powder of cobalt ferrite particles, the average aspect ratio and the average particle size of the magnetic powder are obtained in the same way as in the case where the magnetic powder contains ε-iron oxide particles.

[0140] The average particle volume of the magnetic powder is preferably 2000 nm 3 or less, preferably 1900 nm 3 or less, more preferably 1800 nm 3 or less and more preferably 1700 nm 3 or less, 1600 nm 3 or less or 1500 nm 3 or less. The average particle volume of the magnetic powder is preferably 500 nm 3 or more and preferably 700 nm 3 or more.

[0141] In the case where the average particle volume of the magnetic powder is less than or equal to the above upper limit (e.g. 2000 nm3 or less), preferable electromagnetic conversion characteristics (e.g., SNR) can be achieved in the high-density magnetic recording medium 10. In the case where the average particle volume of the magnetic powder is greater than or equal to the above-mentioned lower limit (e.g., 500 nm 3 or more), the dispersibility of the magnetic powder is further improved and more excellent electromagnetic conversion properties (e.g., SNR) can be achieved. (Binder)

[0142] As the binder, a resin having a structure in which a crosslinking reaction is performed on a polyurethane resin, a vinyl chloride resin, or the like is preferable. However, the binder is not limited to this, and other resins can be appropriately blended depending on the physical properties and the like required for the magnetic recording medium 10. The resin to be blended is not particularly limited as long as it is a resin commonly used in the coating-type magnetic recording medium 10.

[0143] As a binder, for example, one selected from the group consisting of polyvinyl chloride, polyvinyl acetate, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinylidene chloride copolymer, a vinyl chloride-acrylonitrile copolymer, an acrylate ester copolymer, an acrylate ester-vinyl chloride-vinylidene chloride copolymer, an acrylate ester-vinylidene chloride copolymer, a methacrylic acid ester-vinylidene chloride copolymer, a methacrylic acid ester-vinyl chloride copolymer, a methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, a vinylidene chloride-acrylonitrile copolymer, an acrylonitrile-butadiene copolymer, a polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), a styrene-butadiene copolymer, a polyester resin, an amino resin and synthetic rubber, or a combination used by two or more of them.

[0144] Furthermore, a thermosetting resin or a reactive resin can be used as the binder. Examples of the thermosetting resin or the reactive resin include a phenolic resin, an epoxy resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, a polyamine resin, and a urea-formaldehyde resin.

[0145] Additionally, a polar functional group such as -SO3M, -OSO3M, -COOM, and P=O(OM)2 can be introduced into any of the above-mentioned binders to improve the dispersibility of the magnetic powder. Here, M represents a hydrogen atom or an alkali metal such as lithium, potassium, and sodium.

[0146] Further, examples of the polar functional groups include those of the side chain type having an end group of --NR1R2, -NR1R2R3 + X - and those of the main chain type from >NR1R2 + X -Here, R1, R2, and R3 in the formula each independently represent a hydrogen atom or a hydrocarbon group, and X- represents, for example, a halogen element ion such as fluorine, chlorine, bromine, and iodine, or an inorganic or organic ion. Further, examples of the polar functional group include -OH-, -SH-, -CN-, and epoxy groups. The amount of these polar functional groups to be introduced into the binder is preferably 10 -1 up to 10 -8 mol / g and more preferably 10 -2 up to 10 -6 mol / g. (Lubricant)

[0147] The above-mentioned magnetic layer may contain a lubricant. The above-mentioned lubricant may, for example, be one or two or more kinds selected from fatty acids and / or fatty acid esters, and may preferably contain both fatty acids and fatty acid esters. The above-mentioned fatty acid may advantageously be a compound represented by the following general formula (1) or (2). For example, one of the compounds represented by the following general formula (1) and the compound represented by the general formula (2) may be contained as the above-mentioned fatty acid, or both may be contained.

[0148] Furthermore, the above-mentioned fatty acid ester may advantageously be a compound represented by the following general formula (3) or (4). For example, one of the compounds represented by the following general formula (3) and the compound represented by the general formula (4) may be included as the above-mentioned fatty acid ester, or both may be included.

[0149] When the above-mentioned lubricant contains one or both of the compound represented by the general formula (1) and the compound represented by the general formula (2) and one or both of the compound represented by the general formula (3) and the compound represented by the general formula (4), it is possible to suppress the increase of the dynamic friction coefficient due to the repeated recording or reproduction of the magnetic recording medium. CH3 (CH2) k COOH (1)

[0150] (However, in the general formula (1), k represents an integer selected from the range of 14 or more and 22 or less, and more preferably from the range of 14 or more and 18 or less.) CH3 (CH2) n CH=CH (CH2) m COOH (2)

[0151] (However, in the above general formula (2), the sum of n and m is an integer selected from the range of 12 or more and 20 or less, and more preferably from the range of 14 or more and 18 or less.) CH3 (CH2) p COO (CH2) q CH3 (3)

[0152] (However, in the general formula (3), p represents an integer selected from the range of 14 or more and 22 or less, and more preferably 14 or more and 18 or less, and q represents an integer selected from the range of 2 or more and 5 or less, and more preferably the range of 2 or more and 4 or less.) CH3 (CH2) r COO- (CH2) s CH (CH3) 2 (4)

[0153] (However, in the above general formula (4), r represents an integer selected from the range of 14 or more and 22 or less, and s represents an integer selected from the range of 1 or more and 3 or less.)

[0154] Examples of the lubricant include esters of monobasic fatty acids having 10 to 24 carbon atoms and one of monohydric to hexahydric alcohols having 2 to 12 carbon atoms, mixed esters thereof, difatty acid esters, and trifatty acid esters. Specific examples of the lubricant include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, isooctyl stearate, and octyl myristate. (Antistatic agent)

[0155] Examples of the antistatic agent include carbon black, natural surfactants, nonionic surfactants and cationic surfactants. (abrasives)

[0156] Examples of the abrasive include α-alumina having a pregelatinization rate of 90% or more, 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, zirconia, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, acicular α-iron oxide obtained by dehydrating and curing the raw material of magnetic iron oxide, and those surface-treated with aluminum and / or silicon dioxide as required. (hardening agent)

[0157] Examples of the curing agent include polyisocyanate. Examples of the polyisocyanate include aromatic polyisocyanates such as an adduct of tolylene diisocyanate (TDI) and an active hydrogen compound, and aliphatic polyisocyanates such as an adduct of hexamethylene diisocyanate (HMDI) and an active hydrogen compound. The weight-average molecular weight of these polyisocyanates is desirably in the range of 100 to 4500. (rust inhibitor)

[0158] Examples of the rust inhibitor include phenols, naphthols, quinones, heterocyclic compounds containing a nitrogen atom, heterocyclic compounds containing an oxygen atom, and heterocyclic compounds containing a sulfur atom. (Non-magnetic reinforcing particles)

[0159] Examples of the non-magnetic reinforcing particles include alumina (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). (lower class)

[0160] The undercoat layer 12 is a non-magnetic layer containing a non-magnetic powder and a binder. The undercoat layer 12 may further contain at least one additive selected from a lubricant, an antistatic agent, a curing agent, a rust inhibitor, or the like, if necessary.

[0161] The average thickness of the underlayer 12 is preferably 0.6 μm or more and 2.0 μm or less, and more preferably 0.6 μm or more and 1.4 μm or less. Note that the average thickness of the underlayer 12 is obtained in the same way as the average thickness of the magnetic layer 13. However, the magnification of the TEM image is appropriately adjusted according to the thickness of the underlayer 12.

[0162] In an advantageous embodiment of the present disclosure, the underlayer 12 is provided between the magnetic layer 13 and the base 11, and the average thickness of the underlayer 12 may be 2.0 µm or less. (Non-magnetic powder)

[0163] The non-magnetic powder includes, for example, an inorganic particle powder and / or an organic particle powder. Further, the non-magnetic powder may contain a carbon powder such as carbon black. Note that only one type of non-magnetic powder may be used, or two or more types of non-magnetic powder may be used in combination. The inorganic particles contain, for example, a metal, a metal oxide, a metal carbonate, a metal sulfate, a metal nitride, a metal carbide, or a metal sulfide. Examples of the shape of the non-magnetic powder include various shapes such as a needle shape, a spherical shape, a cubic shape, and a plate shape, but are not limited to these shapes. (Binder)

[0164] The description regarding the binder contained in the above-mentioned magnetic layer 13 also applies to the binder contained in the underlayer. (additive)

[0165] The description regarding the lubricant, the antistatic agent, the hardening agent and the rust inhibitor contained in the above-mentioned magnetic layer 13 also applies to the lubricant, the antistatic agent, the hardening agent and the rust inhibitor contained in the underlayer. (Back layer)

[0166] The backing layer 14 may contain a binder and a non-magnetic powder. The backing layer 14 may further contain an additive of a lubricant, a curing agent, an antistatic agent, or the like, as needed. The description regarding the binder and the non-magnetic powder contained in the above-mentioned underlayer 12 also applies to the binder and the non-magnetic powder contained in the backing layer.

[0167] The average particle size of the non-magnetic powder is preferably 10 nm or more and 150 nm or less, more preferably 15 nm or more and 110 nm or less. The average particle size of the non-magnetic powder is obtained in a manner similar to the average particle size of the above-mentioned magnetic particle. The non-magnetic powder may include a non-magnetic powder having two or more particle size distributions.

[0168] The average thickness of the back layer 14 (also referred to as “average thickness t b ' or 't b ”) is advantageously 0.6 µm or less. If the average thickness t bof the back layer 14 is within the above-mentioned range, the thickness of the underlayer 12 and the base 11 can be kept thick even when the average thickness of the magnetic recording medium 10 is 5.3 µm or less. As a result, it is possible to maintain the running stability of the magnetic recording medium 10 in a recording / reproducing device. The lower limit of the average thickness t b of the back layer 14 is not particularly limited, but is, for example, 0.2 µm or more.

[0169] In an advantageous embodiment of the present disclosure, the back layer 14 is provided on the surface of the two surfaces of the base 11 opposite to the surface on which the magnetic layer 13 is provided, and the average thickness of the back layer 14 may be 0.6 µm or less.

[0170] The average thickness tb of the back layer 14 is obtained as follows. First, the average thickness t T of the magnetic recording medium 10. The method for measuring the average thickness t T is described below. Subsequently, the back layer 14 of the sample is removed using a solvent such as MEK (methyl ethyl ketone) and dilute hydrochloric acid. Next, the thickness of the sample is measured at five or more points using a laser holometry instrument (LGH-110C) manufactured by Mitutoyo, and the measured values are simply averaged (arithmetically averaged) to obtain an average value t B [µm]. Then, the average thickness tb [µm] of the back layer 14 is obtained from the following formula. Note that the measurement positions are randomly selected from the sample. tb[μm]=tT[μm]−tB[μm] (Average thickness t Tof the magnetic recording medium)

[0171] The average thickness of the magnetic recording medium 10 (also referred to as “average thickness t T ' or 't T ") is preferably 5.3 µm or more, more preferably 5.2 µm or less, and may even more preferably be 5.1 µm or more, 5.0 µm or less, 4.8 µm or less, or 4.6 µm or less. When the average thickness t T of the magnetic recording medium 10 is within the above-mentioned numerical range (e.g., t T ≤ 5.6 µm), the recording capacity in a data cartridge can be increased compared to the existing data cartridge. The lower limit of the average thickness t T of the magnetic recording medium 10 is not particularly limited, but satisfies, for example, the relationship: 3.5 µm ≤ t T .

[0172] The average thickness t Tof the magnetic recording medium 10 is obtained as follows. First, the magnetic recording medium 10 is prepared with a width of 1 / 2 inch and cut into a length of 250 mm to prepare a sample. Next, using a laser holometry instrument (LGH-110C) manufactured by Mitutoyo as the measuring instrument, the thickness of the sample is measured at five or more points, and the measured values are simply averaged (arithmetically averaged) to obtain the average value t T [µm]. Please note that the measurement positions are randomly selected from the sample. (Coercive force Hc1 in vertical direction)

[0173] The coercive force Hc1 in the perpendicular direction is 4500 Oe or less, more preferably 3500 Oe or less, and even more preferably 3000 Oe or less, 2900 Oe or less, or 2850 Oe or less. A large coercive force Hc1 is preferable because it is less susceptible to thermal disturbances and demagnetizing fields. If the coercive force Hc1 exceeds 4500 Oe, there is a possibility that saturated recording by the recording head will become difficult. As a result, unrecordable portions will remain, and noise will increase, thereby deteriorating the electromagnetic conversion characteristics (e.g., SNR).

[0174] The coercive force Hc1 in the perpendicular direction is preferably 500 Oe or more, more preferably 1000 Oe or more, and may even more preferably be 1500 Oe or more, 2000 Oe or more, 2100 Oe or more, 2200 Oe or more, 2300 Oe or more, or 2400 Oe or more. When the coercive force Hc1 is greater than or equal to the above-mentioned lower limit, it is possible to suppress a decrease in electromagnetic conversion characteristics (e.g., SNR) in high-temperature environments due to the influence of thermal disturbances and the influence of a demagnetizing field.

[0175] The coercive force Hc1 in the perpendicular direction is obtained as follows. First, three sheets of the magnetic recording medium 10 are superimposed with double-sided tapes and then punched with a φ6.39 mm punch to prepare a measurement sample. At this time, markings are made with any ink that does not exhibit magnetism so that the longitudinal direction (running direction) of the magnetic recording medium can be detected. Then, using a vibration sample magnetometer (VSM), the MH loop of the measurement sample (the entire magnetic recording medium 10) is measured according to the perpendicular direction of the magnetic recording medium 10 (the thickness direction of the magnetic recording medium 10). Next, acetone, ethanol, or the like is used to wipe off the coating film (the undercoat layer 12, the magnetic layer 13, the back layer 14, and the like), leaving only the base 11.Then, three layers of the obtained bases 11 are superimposed with double-sided tapes and then punched with a φ6.39 mm punch to obtain a background correction sample (hereinafter referred to simply as the correction sample). The VSM is then used to measure the MH loop of the correction sample (the base 11), which corresponds to the perpendicular direction of the base 11 (the thickness direction of the magnetic recording medium 10).

[0176] A high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by TOEI INDUSTRY CO., LTD. is used to measure the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (base 11). The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, lock amplifier time constant: 0.3 s, waiting time: 1 s, and MH average count: 20.

[0177] After obtaining two MH loops, background correction is performed by subtracting the MH loop of the sample for correction (the base 11) from the MH loop of the measurement sample (the entire magnetic recording medium 10) to obtain the MH loop after background correction. The measurement / analysis program included with the "Type VSMP7-15" is used to calculate the background correction.

[0178] The coercive force Hc1 in the perpendicular direction is obtained from the obtained MH loop after background correction. Note that the measurement / analysis program associated with the "VSM-P7-15" type is used for this calculation. Note that the above-mentioned MH loop measurement is performed at 25°C. Furthermore, the "demagnetization field correction" is not performed when measuring the MH loop in the perpendicular direction of the magnetic recording medium 10. (Coercive force Hc2 in the longitudinal direction)

[0179] The coercive force Hc2 in the longitudinal direction is preferably 2000 Oe or less, more preferably 1900 Oe or less, and even more preferably 1800 Oe or less. When the coercive force Hc2 in the longitudinal direction is 2000 Oe or less, a favorable recording pattern can be formed because the magnetization is sensitive to the magnetic field in the perpendicular direction from the recording head.

[0180] The coercive force Hc2 in the longitudinal direction is preferably 1000 Oe or more. When the coercive force Hc2 in the longitudinal direction is 1000 Oe or more, it is possible to suppress demagnetization due to the leakage flux from the recording head.

[0181] The above-mentioned coercive force Hc2 is obtained as follows.

[0182] First, three sheets of the magnetic recording medium 10 are superimposed with double-sided tapes and then punched with a φ6.39 mm punch to prepare a measurement sample. At this time, markings are made with any non-magnetic inks so that the longitudinal direction (running direction) of the magnetic recording medium 10 can be detected.

[0183] Then, using a vibration sample magnetometer (VSM), the MH loop of the measurement sample (the entire magnetic recording medium 10) is measured according to the longitudinal direction (travel direction) of the magnetic recording medium 10. Next, acetone, ethanol, or the like is used to wipe off the coating film (the undercoat layer 12, the magnetic layer 13, the back layer 14, and the like), leaving only the base 11. Then, three layers of the obtained bases 11 are superimposed with double-sided tapes and then punched out with a φ6.39 mm punch to obtain a background correction sample (hereinafter simply referred to as a correction sample). The VSM is then used to measure the MH loop of the correction sample (the base 11) corresponding to the longitudinal direction of the base 11 (the longitudinal direction of the magnetic recording medium 10).

[0184] A high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by TOEI INDUSTRY CO., LTD. is used to measure the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (base 11). The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, lock amplifier time constant: 0.3 s, waiting time: 1 s, and MH average count: 20.

[0185] After obtaining the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the sample for correction (base 11), background correction is performed by subtracting the MH loop of the sample for correction (base 11) from the MH loop of the measurement sample (the entire magnetic recording medium 10) to obtain the MH loop after background correction. The measurement / analysis program included with the "Type VSMP7-15" is used to calculate the background correction.

[0186] The coercive force Hc2 is obtained from the obtained MH loop after background correction. Note that the measurement / analysis program associated with the "VSM-P7-15" type is used for this calculation. Note that the above-mentioned MH loop measurement is performed at 25°C. Furthermore, the "demagnetization field correction" is not performed when measuring the MH loop in the longitudinal direction of the magnetic recording medium 10. (Hc2 / Hc1)

[0187] A ratio Hc2 / Hc1 of the coercive force Hc2 in the longitudinal direction to the coercive force Hc1 in the perpendicular direction satisfies the following relationship: Hc2 / Hc1 ≤ 0.8, preferably Hc2 / Hc1 ≤ 0.75, more preferably Hc2 / Hc1 ≤ 0.7, even more preferably, for example, Hc2 / Hc1 ≤ 0.65, and particularly preferably Hc2 / Hc1 ≤ 0.6. When the coercive forces Hc1 and Hc2 satisfy the above-mentioned relationship, the degree of perpendicular alignment of the magnetic powder can be improved. Therefore, the magnetization transition width can be narrowed, and a high-output signal can be obtained at the time of signal reproduction. It is possible to improve the electromagnetic conversion characteristics (e.g., C / N). It should be noted that, as described above, a preferable recording pattern can be formed when Hc2 is low because the magnetization is sensitive to the magnetic field in the perpendicular direction from the recording head.

[0188] In the case where the ratio Hc2 / Hc1 satisfies the following relationship: Hc2 / Hc1 ≤ 0.8, it is particularly advantageous if the average thickness of the magnetic layer 13 is 90 nm or less. If the average thickness of the magnetic layer 13 exceeds 90 nm, in the case where a ring-type head is used as the recording head, the lower region of the magnetic layer 13 (region on the underlayer 12 side) is magnetized in the longitudinal direction, and there is a possibility that the magnetic layer 13 cannot be magnetized uniformly in the thickness direction. Therefore, even if the ratio Hc2 / Hc1 satisfies the relationship Hc2 / Hc1 ≤ 0.8 (that is, the degree of perpendicular orientation of the magnetic powder is increased), there is a possibility that electromagnetic conversion characteristics (e.g., C / N) cannot be improved.

[0189] The lower limit of Hc2 / Hc1 is not particularly restricted, but satisfies, for example, the following relationship: 0.5 ≤ Hc2 / Hc1.

[0190] Note that Hc2 / Hc1 represents the degree of perpendicular orientation of the magnetic powder. The smaller Hc2 / Hc1, the higher the degree of perpendicular orientation of the magnetic powder. The reason why Hc2 / Hc1 is used as an index representing the degree of perpendicular orientation of the magnetic powder in this embodiment will be described below.

[0191] A perpendicularity ratio SQ (= (Mr / Ms)×100, where Mr(emu): residual magnetization, Ms(emu): saturation magnetization) has been commonly used in the past as an index (parameter) representing the degree of perpendicularity of the magnetic powder. However, the perpendicularity ratio index SQ is no more suitable than Hc2 / Hc1 as an index representing the degree of perpendicularity of the magnetic powder for the following reason. (1) The perpendicularity ratio SQ varies depending on the value of the coercive force Hc of the magnetic powder. For example, as shown in Fig. 7, the perpendicularity ratio SQ appears to increase as the coercive force Hc of the magnetic powder increases. (2) The perpendicularity ratio SQ is affected by distortion of the MH loop due to overdispersion.

[0192] In this regard, in this embodiment, Hc2 / Hc1 can be used as an index that more appropriately represents the orientation degree of the magnetic powder. Since the coercive forces Hc1 and Hc2 simply vary depending on the orientation direction of the magnetic powder, Hc2 / Hc1 is more suitable as an index for the orientation degree of the magnetic powder. (Residual coercivity Hrp and ratio Hrp / Hc1)

[0193] In the magnetic recording medium according to the present disclosure, the ratio Hrp / Hc1 of the residual coercive force Hrp of the magnetic recording medium measured using the pulsed magnetic field to the coercive force Hc1 of the above-mentioned magnetic recording medium in the perpendicular direction is 2.10 or less, preferably 2.05 or less, and more preferably 2.00 or less, and may be even more preferably 1.95 or less, 1.90 or less, or 1.85 or less. In the magnetic recording medium according to the present disclosure, when the ratio Hrp / Hc1 is within the above-mentioned numerical range, it is excellent in preservation stability even though the average particle volume of the magnetic powder is small.

[0194] The above-mentioned ratio Hrp / Hc1 may be, for example, 0 or more, 0.50 or more, or 1.00 or more.

[0195] Hc1, which is used to calculate the above-mentioned ratio Hrp / Hc1, is measured as described above.

[0196] Hrp, which is used to calculate the above-mentioned ratio Hrp / Hc1, is obtained as follows.

[0197] A sample similar to the sample used for calculating the coercive force Hc1 is prepared as a measurement sample, and a residual magnetization curve in the direction perpendicular to the film surface is obtained using an evaluation device HR-PVSM20 manufactured by HAYAMA Co. with fast response characteristics as follows.

[0198] First, a magnetic field of approximately -3980 kA / m (-50 kOe) is applied to the sample in the perpendicular direction, and the magnetic field is returned to zero to achieve a residual magnetization state. Then, a magnetic field of approximately 40.2 kA / m (approximately 505 Oe) is applied in the opposite direction, and the magnetic field is returned to zero to measure the residual magnetization amount. The magnetic field applied at this time is a pulsed magnetic field with a pulse width of 10 -8s. Afterward, the measurement of applying a magnetic field approximately 40.2 kA / m larger than the previously applied magnetic field to reset the magnetic field to zero is repeated in the same manner, and the residual magnetization amount is plotted against the applied magnetic field to construct a DCD curve. The measured magnetic field is up to approximately 20 kOe. Note that background correction and demagnetizing field correction are not performed. The measurement conditions are shown below. Initial magnetization voltage: 220 V (equivalent to -3980 kA / m) Measurement start voltage: 0 V (corresponds to 0 Oe) Step voltage: 17.5 V (corresponds to approx. 505 Oe) Maximum voltage: 350 V (equivalent to 20 kOe) Latching amplifier waiting time: 10 seconds

[0199] For example, the Fig. The residual magnetization curve shown in Figure 8 is obtained from the data obtained by the above-mentioned measurement. Phase correction is performed as needed to obtain a residual magnetization curve from the data. The phase correction is described below. Of the points constituting the obtained residual magnetization curve, two points enclosing the X-axis (two points closest to the X-axis) are connected by a straight line, and the point where the straight line intersects the X-axis is calculated as Hrp.

[0200] Phase correction is described in more detail below.

[0201] Although the unit of magnetization volume is originally emu, the magnetization volume is output as a voltage V for each applied magnetic field, and either a positive or negative value of the magnetization volume (voltage V) for each applied magnetic field is output as a positive value with respect to the above-mentioned evaluation device with fast response characteristics. Therefore, it is necessary to perform phase correction for each applied magnetic field. The phase information data included in the output of the evaluation device with fast response characteristics is used for the correction. In addition, the phase information data for each applied magnetic field is output along with the magnetization volume (voltage V) for each applied magnetic field.

[0202] In the case where the phase information data of the measured magnetization volume (voltage V) for a specific magnetic field is a negative value, the measured magnetization volume (voltage V) must be multiplied by "-1," and a value obtained by multiplying the measured magnetization volume (voltage V) by "-1" is used to obtain a residual magnetization curve. The multiplication by "-1" is the phase correction mentioned above.

[0203] In the case where the phase information data of the measured magnetization volume (voltage V) for a certain magnetic field is a positive value, the measured magnetization volume (voltage V) does not need to be multiplied by "-1" and the measured magnetization volume (voltage V) is used to obtain a residual magnetization curve.

[0204] By plotting the magnetization volume after phase correction (multiplied by “-1”) obtained as described above and the measured magnetization volume (not multiplied by “-1”) with respect to the magnetic field, the residual magnetization curve is obtained as shown in Fig. 8 is shown. (Thermal stability)

[0205] The thermal stabilization K u V act / k B For example, T of the magnetic recording medium according to the present disclosure is 60 or more, preferably 63 or more, and more preferably 65 or more, and may be even more preferably 67 or more, 70 or more, 73 or more, or 75 or more. Although the magnetic powder having a small average particle volume is contained, the magnetic recording medium according to the present disclosure has such high thermal stability that it has excellent preservation stability.

[0206] The thermal stability K u V act / k B T of the magnetic recording medium according to the present disclosure may be, for example, 150 or less or 100 or less.

[0207] The thermostability K u V act / k B T of the magnetic recording medium can be achieved, for example, by stabilizing the material state after glass dissolution during the process of synthesizing the magnetic powder. Although the dissolution temperature is arbitrarily set at the time of glass dissolution, for example, the amorphous state of the material after glass dissolution is further uniformed by setting the dissolution temperature at this time to a high temperature, thereby making it possible to stabilize the material state. Furthermore, the thermal stability K u V act / k BT can also be adjusted by improving the degree of vertical alignment.

[0208] The thermal stability K u V act / k B T of the magnetic recording medium (Ku: magnetocrystalline anisotropy constant of the magnetic powder, V act : Activation volume of the magnetic powder, k B : Boltzmann constant, T: absolute temperature) is calculated using the Sherlock equation shown below (Reference documents: IEEE TRANSACTIONS ON MAGNETICS, VOLUME 50, NO. 11, NOVEMBER 2014, and J. Flanders and M.P. Sharrock: J. Appl. Phys., 62, 2918 (1987)) Hr(t′)=H0[1−{kBT / (KuVact)ln(f0t′ / 0.693)n}] (H r : residual magnetic field, t': magnetization damping amount, H0: magnetic field change amount, kB: Boltzmann constant, T: absolute temperature, Ku: magnetocrystalline anisotropy constant, V act : activation volume of the magnetic powder, f0: frequency factor, n: coefficient)

[0209] It should be noted that (a) the residual magnetic field H r , (b) the magnetization attenuation amount t', and (c) the magnetic field change amount H0 are obtained as follows. Furthermore, the following numerical values are used as (d) the frequency factor f0 and (e) the coefficient n. Furthermore, the absolute temperature T is 25 °C.

[0210] The (a) residual magnetic field H rcan be measured by a pulse VSM "HR-PVSM20" manufactured by HAYAMA Co. Ltd. For the measurement, a sample is prepared using a method similar to the above-mentioned method for measuring coercive force Hc1. Before starting the measurement, a magnetic field of 6358 [Oe] is applied to the sample to magnetically align the sample in one direction. After that, a magnetic field is intermittently applied every 505.75 [Oe] from 0 to 20230 [Oe]. The magnetization volume at this time is measured, and the values are plotted with the applied magnetic field as the X-axis and the magnetization volume as the Y-axis. The X at Y = 0 in the obtained graph is the residual magnetic field H. r .

[0211] (b) The magnetization attenuation amount t' is obtained as follows. Namely, by applying an external magnetic field near the coercive force Hc of the magnetic recording medium to be measured under three conditions, a sample obtained by the preparation method similar to the above-mentioned method for measuring the coercive force Hc1 is used to measure the magnetization attenuation amount similarly to the above-mentioned method for measuring the coercive force Hc1 by the VSM. Then, the magnetization attenuation amount t' is calculated from the magnetization attenuation amount using the Flanders equation described in the following reference (Reference: IPJ Flanders and MP Sharrock, "An Analysis of Time-Dependent Magnetization and Coercivity and of Their Relationship to Print-Through in Recording Tapes," J. Appl. Phys., Vol. 62, pp. 2918-2928, 1987).

[0212] Here, "coercive force Hc" refers to the coercive force Hc in the alignment direction of the magnetic powder. That is, when the magnetic powder is aligned in the vertical direction, "coercive force Hc" refers to the coercive force Hc1 in the vertical direction. Meanwhile, when the magnetic powder is aligned in the longitudinal direction, "coercive force Hc" refers to the coercive force Hc2 in the longitudinal direction. When the magnetic powder is not aligned, that is, when there is no alignment, "coercive force Hc1" refers to the coercive force Hc1 in the vertical direction.

[0213] Furthermore, the "external magnetic field under three conditions" means a magnetic field greater than or equal to the coercive force Hc (a magnetic field in which positive magnetization is obtained), a magnetic field near the coercive force Hc (a magnetic field in which magnetization close to zero is obtained), and a magnetic field below the coercive force Hc (a magnetic field in which negative magnetization is obtained). As a specific example, in the case where the tape with perpendicular orientation Hc = 2600 [Oe], the "external magnetic field under the three conditions" is calculated with the magnetic field in which positive magnetization is obtained = 2400 [Oe], the magnetic field near the coercive force Hc = 2600 [Oe], and the magnetic field in which negative magnetization is obtained = 2800 [Oe]. However, the numerical values given as a specific example do not limit the numerical range in actual measurement.

[0214] The (c) magnetic field change amount H0 is a constant obtained by substituting the measurement magnetic field measured in (b) and the magnetization attenuation amount into the Sherlock equation for calculation.

[0215] The (d) frequency factor f0 is a constant value and f0=5.0×10 9 Hz.

[0216] The (e) coefficient n is set to a value corresponding to the magnetocrystalline anisotropy of the magnetic powder. In the case where the magnetic powder has uniaxial magnetocrystalline anisotropy and the magnetic tape is vertically aligned, n is set to 0.5. In the case where the magnetic powder has multiaxial magnetocrystalline anisotropy (triaxial magnetocrystalline anisotropy) or the magnetic powder has uniaxial magnetocrystalline anisotropy but the magnetic tape is not aligned, n is set to 0.77. (2) Method for producing a magnetic recording medium

[0217] Next, a method for manufacturing the magnetic recording medium 10 having the above-mentioned configuration will be described. First, a coating material for forming an undercoat layer is prepared by kneading and dispersing a non-magnetic powder, a binder, and the like in a solvent. Next, a coating material for forming a magnetic layer is prepared by kneading and dispersing a magnetic powder, a binder, and the like in a solvent. For preparing the coating material for forming a magnetic layer and the coating material for forming an undercoat layer, the following solvents, dispersing devices, and kneading devices can be used, for example.

[0218] Examples of the solvent used for preparing coating materials include a ketone solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; an alcohol solvent such as methanol, ethanol, and propanol; an ester solvent such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol acetate; an ether solvent such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; an aromatic hydrocarbon solvent such as benzene, toluene, and xylene; and a halogenated hydrocarbon solvent such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene. These can be used alone or appropriately mixed and used.

[0219] As the above-mentioned kneading device used for producing the coating materials, for example, a kneading device such as a continuous twin-screw kneader, a continuous twin-screw kneader capable of multi-stage dilution, a kneader, a pressure kneader, and a roller kneader can be used. However, the present technology is not specifically limited to these devices. Furthermore, as the above-mentioned dispersing device used for producing the coating materials, for example, a dispersing device such as a roller mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a bead mill (e.g., "DCP Mill" manufactured by Eirich Co. Ltd.), a homogenizer, and an ultrasonic disperser can be used. However, the present technology is not specifically limited to these devices.

[0220] Next, the coating material for forming an undercoat layer is applied to one main surface of the base 11 and dried to form the undercoat layer 12. Then, the coating material for forming a magnetic layer is applied to this undercoat layer 12 and dried to form the magnetic layer 13 on the undercoat layer 12. Note that the magnetic field of the magnetic powder is aligned in the thickness direction of the base 11 during drying, for example, by an electromagnetic coil. Further, the magnetic field of the magnetic powder may be aligned in the running direction (longitudinal direction) of the base 11 during drying, for example, by an electromagnetic coil, and then aligned in the thickness direction of the base 11. With such magnetic field alignment processing, it is possible to lower the ratio Hc2 / Hc1.Therefore, the degree of perpendicular alignment of the magnetic powder can be improved. After the magnetic layer 13 is formed, the back layer 14 is formed on the other main surface of the base 11. As a result, the magnetic recording medium 10 is obtained.

[0221] The ratio Hc2 / Hc1 is set to a desired value by adjusting, for example, the strength of the magnetic field for forming a magnetic layer applied to the coating film of the coating material, the concentration of the solid content in the coating material for forming a magnetic layer, and the drying conditions (drying temperature and drying time) of the coating film of the coating material for forming a magnetic layer. The strength of the magnetic field applied to the coating film is preferably not less than twice and not more than three times the coercive force of the magnetic powder. To further increase the ratio Hc2 / Hc1, it is preferable to improve the dispersed state of the magnetic powder in the coating material for forming a magnetic layer.To further increase the Hc2 / Hc1 ratio, it is also effective to magnetize the magnetic powder in a stage before the coating material for forming a magnetic layer enters the alignment device to cause the magnetic field of the magnetic powder to be aligned. Note that the above-mentioned methods for adjusting the Hc2 / Hc1 ratio can be used alone or two or more of them can be used in combination.

[0222] The Hrp / Hc1 ratio can be controlled, for example, by adjusting the alignment condition during magnetic field alignment processing and / or adjusting the coercive force of the magnetic powder. Furthermore, the Hrp / Hc1 ratio can also be adjusted by changing the type of magnetic powder, the average particle volume, the average aspect ratio, or the average particle size of the magnetic powder. Afterwards, the resulting

[0223] Magnetic recording medium 10 is wound around the large-diameter core, and curing processing is performed on it. Finally, the magnetic recording medium 10 is calendered and cut to a predetermined width (e.g., 1 / 2 inch wide). In this way, a desired elongated magnetic recording medium 10 can be obtained. (3) Recording / playback device [Configuration of the recording / playback device]

[0224] Next, an example of a configuration of a recording / reproducing apparatus 30 for recording and reproducing the magnetic recording medium 10 having the above-mentioned configuration will be described with reference to Fig. 9 described.

[0225] The recording / reproducing device 30 has a configuration capable of adjusting the voltage applied to the longitudinal direction of the magnetic recording medium 10. Furthermore, the recording / reproducing device 30 has a configuration capable of loading a magnetic recording cartridge 10A. For convenience of explanation, the recording / reproducing device 30 has a configuration capable of loading a single magnetic recording cartridge 10A. However, the recording / reproducing device 30 may have a configuration capable of loading a plurality of magnetic recording cartridges 10A.

[0226] The recording / reproducing device 30 is connected to an information processing device such as a server 41 and a personal computer (hereinafter referred to as "PC") 42 via a network 43, and is configured to record data supplied from these information processing devices onto the magnetic recording cartridge 10A. The shortest recording wavelength of the recording / reproducing device 30 is preferably 100 nm or less, more preferably 75 nm or less, even more preferably 60 nm or less, and particularly preferably 50 nm or less.

[0227] As it is in Fig. 9, the recording / reproducing device 30 includes a spindle 31, a recording / reproducing device side reel 32, a spindle driving device 33, a reel driving device 34, a plurality of guide rollers 35, a head unit 36, a communication interface (hereinafter I / F) 37, and a control device 38.

[0228] The spindle 31 is configured to load the magnetic recording cartridge 10A. The magnetic recording cartridge 10A conforms to the Linear Tape Open (LTO) standard and rotatably includes a single reel 10C, on which the magnetic recording medium 10 is wound, within a cartridge case 10B. An inverted V-shaped servo pattern is prerecorded as a servo signal on the magnetic recording medium 10. The reel 32 is configured to fix the distal end of the magnetic recording medium 10 pulled out from the magnetic recording cartridge 10A.

[0229] The spindle drive device 33 is a device that rotates the spindle 31. The reel drive device 34 is a device that rotates the reel 32. When recording or reproducing data to or from the magnetic recording medium 10, the spindle drive device 33 and the reel drive device 34 rotate the spindle 31 and the reel 32, respectively, to drive the magnetic recording medium 10. The guide roller 35 is a roller for guiding the movement of the magnetic recording medium 10.

[0230] The head unit 36 includes a plurality of recording heads for recording data signals on the magnetic recording medium 10, a plurality of reproducing heads for reproducing data signals recorded on the magnetic recording medium 10, and a plurality of servo heads for reproducing the servo signal recorded on the magnetic recording medium 10. For example, a ring-type head may be used as the recording head, but the type of the recording head is not limited thereto.

[0231] The communication I / F 37 is used to communicate with an information processing device such as the server 41 and the PC 42 and is connected to the network 43.

[0232] The control device 38 controls the entire recording / reproducing device 30. For example, the control device 38 records data signals supplied from the information processing device onto the magnetic recording medium 10 through the head unit 36 in response to a request from the information processing device such as the server 41 and the PC 42. Further, the control device 38 reproduces the data signal recorded on the magnetic recording medium 10 and supplies the reproduced data signal to the information processing device through the head unit 36 in response to a request from the information processing device such as the server 41 and the PC 42. [Operation of the recording / playback device]

[0233] Next, the operation of the recording / reproducing device 30 having the above-mentioned configuration will be described.

[0234] First, the magnetic recording cartridge 10A is loaded into the recording / reproducing device 30, and the distal end of the magnetic recording medium 10 is pulled out and transferred to the reel 32 via the plurality of guide rollers 35 and the head unit 36, and fixed to the reel 32.

[0235] Next, when an operation unit (not shown) is operated, the spindle drive device 33 and the reel drive device 34 are driven under the control of the control device 38, and the spindle 31 and the reel 32 are caused to rotate in the same direction, so that the magnetic recording medium 10 moves from the reel 10C to the reel 32. While the magnetic recording medium 10 is wound onto the reel 32, the head unit 36 records information on the magnetic recording medium 10 or reproduces recorded information on the magnetic recording medium 10.

[0236] Furthermore, in the case where the magnetic recording medium 10 is rewound onto the reel 10C, the spindle 31 and the reel 32 are rotationally driven in the direction opposite to the above-mentioned direction, thereby causing the magnetic recording medium 10 to travel from the reel 32 to the reel 10C. Also in this rewinding, the head unit 36 records information on the magnetic recording medium 10 or reproduces information recorded on the magnetic recording medium 10. (4) Cassette[Cassette configuration]

[0237] The present disclosure also provides a magnetic recording cartridge (also referred to as a tape cartridge) comprising the magnetic recording medium according to the present disclosure. In the magnetic recording cartridge, the magnetic recording medium may, for example, be wound on a reel. The magnetic recording cartridge may, for example, comprise a communication unit that communicates with a recording / reproducing device, a storage unit, and a control unit that stores, in the storage unit, the information received from the recording / reproducing device via the communication unit, reads the information from the storage unit, and transmits the read information to the recording / reproducing device via the communication unit in response to a request from the recording / reproducing device.The information may include adjustment information for adjusting the tension applied to the magnetic recording medium in the longitudinal direction. The adjustment information may include, for example, information regarding the widthwise dimension at a plurality of positions of the magnetic recording medium in the longitudinal direction. The information regarding the widthwise dimension may be dimensional information at the time of manufacture (initially after manufacture) of the magnetic recording medium, which is described below in [Configuration of the Cartridge Memory], and / or dimensional information acquired during recording and / or playback processing of the magnetic recording medium.

[0238] An example of a configuration of the cartridge 10A including the magnetic recording medium 10 having the above-mentioned configuration will be described with reference to Fig. 10 described.

[0239] Fig. 10 is an exploded perspective view showing an example of a configuration of the cassette 10A. The cartridge 10A is a magnetic recording media cartridge conforming to the Linear Tape Open (LTO) standard, and includes, in the cartridge case 10B including a lower shell 212A and an upper shell 212B, the reel 10C on which the magnetic tape (tape-shaped magnetic recording medium 10) is wound, a reel lock 214 and a reel spring 215 for locking the rotation of the reel 10C, a spider 216 for releasing the locked state of the reel 10C, a sliding door 217 for opening and closing a tape outlet 212C provided on the cartridge case 10B across the lower shell 212A and the upper shell 212B, a door spring 218 that biases the sliding door 217 to the closed position of the tape outlet 212C, a Write protection 219 to prevent accidental deletion and a cassette memory 211.The reel 10C has a substantially disc shape with an opening at its center and includes a reel hub 213A and a flange 213B formed of a hard material such as plastic. A guide pin 220 is provided at one end of the magnetic tape 10.

[0240] The cartridge memory 211 is provided near a corner of the cartridge 10A. While the cartridge 10A is loaded into the recording / reproducing device 30, the cartridge memory 211 is caused to face a reader / writer (not shown) of the recording / reproducing device 30. The cartridge memory 211 communicates with the recording / reproducing device 30, specifically, a reader / writer (not shown), using a radio communication standard conforming to the LTO standard. [Cassette Memory Configuration]

[0241] An example of a configuration of the cassette memory 211 will be described with reference to Fig. 11 described.

[0242] Fig. 11 is a block diagram showing an example of a configuration of the cassette memory 211. The cassette memory 211 includes an antenna coil (communication unit) 331 for communicating with a reader / writer (not shown) in a defined communication standard; a rectification / power supply circuit 332 that generates power from radio waves received by the antenna coil 331 using an induced electromotive force and rectifies it to generate a power source; a clock circuit 333 that generates clocks using an induced electromotive force also received from radio waves received by the antenna coil 331; a detection / modulation circuit 334 for detecting radio waves received by the antenna coil 331 and modulating signals transmitted from the antenna coil 331.a controller (a control unit) 335 having a logic circuit and the like for distinguishing commands and data from digital signals extracted from the detection / modulation circuit 334 and for processing the commands and data; and a memory (a storage unit) 336 that stores information. Furthermore, the cassette memory 211 includes a capacitor 337 connected in parallel with the antenna coil 331, and the antenna coil 331 and the capacitor 337 form an oscillation circuit.

[0243] Memory 336 stores information and the like related to cartridge 10A. Memory 336 is non-volatile memory (NVM). The storage capacity of memory 336 is advantageously approximately 32 KB or more. For example, in the case where cartridge 10A conforms to the LTO-9 or LTO-10 standard, memory 336 has a storage capacity of approximately 32 KB.

[0244] The memory 336 has a first storage area 336A and a second storage area 336B. The first storage area 336A corresponds to a storage area of a cartridge memory of the LTO standard prior to LTO8 (hereinafter referred to as "existing cartridge memory") and is an area for storing information conforming to the LTO standard prior to LTO8. The information conforming to the LTO standard prior to LTO8 includes, for example, production information (e.g., a unique number of the cartridge 10A), usage history (e.g., the frequency of tape pulling (thread count)), and the like.

[0245] The second storage area 336B corresponds to an expanded storage area for the storage area of the existing cartridge memory. The second storage area 336B is an area for storing additional information. Here, the additional information means information regarding the cartridge 10A that is not specified in the LTO standard prior to LTO8. Examples of the additional information include, but are not limited to, voltage adjustment information, management account data, index information, and thumbnails of a moving image recorded on the magnetic tape 10. The voltage adjustment information includes a pitch between adjacent servo bands at the time of recording data on the magnetic tape 10 (pitch between servo patterns recorded on adjacent servo bands).The pitch between adjacent servo bands is an example of width-related information regarding the width of the magnetic tape 10. The details of the pitch between servo bands will be described below. In the following description, in some cases, the information stored in the first storage area 336A is referred to as "first information," and the information stored in the second storage area 336B is referred to as "second information."

[0246] The memory 336 may include multiple banks. In this case, the first storage area 336A may be formed by some of the multiple banks, and the second storage area 336B may be formed by the remaining banks. Specifically, for example, in the case where the cartridge 10A conforms to the LTO-9 standard or the LTO-10 standard, the memory 336 may include two banks with storage capacities of approximately 16 KB, where one of the two banks may form the first storage area 336A and the other bank may form the second storage area 336B.

[0247] The antenna coil 331 induces an induced voltage through electromagnetic induction. The controller 335 communicates with the recording / reproducing device 30 according to a defined communication standard via the antenna coil 331. In particular, for example, mutual authentication, sending and receiving commands, data exchange, and the like are performed.

[0248] The controller 335 stores information received from the recording / reproducing device 30 via the antenna coil 331 in the memory 336. The controller 335 reads information from the memory 336 and transmits it to the recording / reproducing device 30 via the antenna coil 331 in response to a request from the recording / reproducing device 30. (5) Effects

[0249] In the magnetic recording medium 10, the average particle volume V of the magnetic powder contained in the magnetic layer 13 is 2000 nm 3 or less, the average thickness t T of the magnetic recording medium 10 is 5.3 µm or less, the thermal stability K u V act / k B T of the magnetic recording medium 10 is 60 or more, and the ratio Hrp / Hc1 of the residual coercive force Hrp of the magnetic recording medium 10, measured using a pulsed magnetic field, and the coercive force Hc1 of the magnetic recording medium 10 in the perpendicular direction is 2.10 or less. As a result, the magnetic recording medium 10 has a high recording density and excellent preservation stability. Furthermore, the magnetic recording medium 10 also has excellent electromagnetic conversion characteristics. (6) Modified Example (Modified Example 1)

[0250] As it is in Fig. 12, the magnetic recording medium 10 may further include a barrier layer 15 provided on at least one surface of the base 11. The barrier layer 15 is a layer for suppressing dimensional change according to the environments of the base 11. For example, hygroscopicity of the base 11 is exemplified as a reason for causing the dimensional change, but it is possible to reduce the speed of moisture penetration into the base 11 by providing the barrier layer 15. The barrier layer 15 contains, for example, a metal or a metal oxide. As the metal, for example, Al, Cu, Co, Mg, Si, Ti, V, Cr, Mn, Fe, Ni, Zn, Ga, Ge, Y, Zr, Mo, Ru, Pd, Ag, Ba, Pt, Au, and / or Ta can be used. As the metal oxide, for example, a metal oxide containing one or two or more of the above-mentioned metals can be used.In particular, for example, Al2O3, CuO, CoO, SiO2, Cr2O3, TiO2, Ta2O5, and / or ZrO2 can be used. Furthermore, the barrier layer 15 can contain diamond-like carbon (DLC), diamond, or the like.

[0251] The average thickness of the barrier layer 15 is preferably 20 nm or more and 1000 nm or less, and more preferably 50 nm or more and 1000 nm or less. The average thickness of the barrier layer 15 is obtained in the same way as the average thickness of the magnetic layer 13. However, the magnification of the TEM image is appropriately adjusted according to the thickness of the barrier layer 15. (Modified Example 2)

[0252] The magnetic recording medium 10 may be incorporated into a library device. That is, the present disclosure also provides a library device including at least one magnetic recording medium 10. The library device has a configuration capable of adjusting the tension applied to the longitudinal direction of the magnetic recording medium 10 and may include a plurality of the recording / reproducing devices 30 described above. 3. Example

[0253] Hereinafter, the present disclosure will be specifically described by way of examples, but the present disclosure is not limited to these examples only.

[0254] In this example, the average thickness of the base film (base), the average thickness of the magnetic layer, the average thickness of the underlayer, the average thickness of the back layer, the average thickness of the magnetic tape (magnetic recording medium), the average aspect ratio of the magnetic powder, the average particle size of the magnetic powder, the average particle volume of the magnetic powder, the coercive force Hc1 of the tape-type magnetic recording medium (also referred to as “magnetic tape”) in the perpendicular direction, the residual coercive force Hrp, and the thermal stability K u V act / k B T (measured at 25 °C) those obtained by the measuring method described in the above-mentioned embodiment. [Example 1] (Process for preparing the coating material for forming the magnetic layer)

[0255] A coating material for forming a magnetic layer was prepared as follows. First, a first composition of the following formulation was kneaded using an extruder. Next, the kneaded first composition and a second composition of the following formulation were placed in a stirring tank equipped with a dispersing device to perform preliminary mixing. Subsequently, sand mill mixing was further performed and filtering was performed to prepare a coating material for forming a magnetic layer. (First composition)

[0256] Magnetic powder (hexagonal ferrite with an M-type structure, composition: Ba ferrite, average particle volume: 1600 nm 3 ): 100 parts by mass Vinyl chloride resin (30 mass% cyclohexanone solution): 60 parts by mass (Polymerization degree 300, Mn = 10000, contains OSO3K = 0.07 mmol / g and secondary OH = 0.3 mmol / g as polar groups.) (Aluminum oxide powder: 5 parts by mass (α-Al2O3, average particle diameter 0.2 µm) Soot: 2 parts by mass (Manufactured by Tokai Carbon Co., Ltd., Trade Name: Seast TA) (Second composition) Vinyl chloride resin: 1.1 parts by mass (Resin solution: resin content 30 mass%, cyclohexanone 70 mass%) N-Butyl stearate: 2 Methyl ethyl ketone: 121.3 parts by mass Toluene: 121.3 parts by mass Cyclohexanone: 60.7 parts by mass

[0257] Finally, as a curing agent, polyisocyanate (trade name: Coronat L, manufactured by Nippon Polyurethane Industry Co., Ltd.): 2 parts by mass and myristic acid: 2 parts by mass were added to the coating material for forming the magnetic layer prepared as described above. (Process for producing a coating material for forming an undercoat layer)

[0258] A coating material for forming an undercoat layer was prepared as follows. First, a third composition of the following formulation was kneaded using an extruder. Next, the kneaded third composition and a fourth composition of the following formulation were placed in a stirring tank equipped with a dispersion device to perform preliminary mixing. Subsequently, sand mill mixing was further performed and filtering was performed to prepare a coating material for forming an undercoat layer. (Third Composition) Acicular iron oxide powder: 100 parts by mass (α-Fe2O3, average length of the major axis 0.15 µm) Vinyl chloride resin: 55.6 parts by mass (Resin solution: resin content 30 mass%, cyclohexanone 70 mass%) Soot: 10 parts by mass (Average particle size 20 nm) (Fourth Composition) Polyurethane resin UR8200 (manufactured by TOYOBO CO., LTD.): 18.5 parts by mass N-butyl stearate: 2 parts by mass Methyl ethyl ketone: 108.2 parts by mass Toluene: 108.2 parts by mass Cyclohexanone: 18.5 parts by mass

[0259] Finally, as a curing agent, polyisocyanate (trade name: Coronat L, manufactured by TOSOH CORPORATION): 2 parts by mass and myristic acid: 2 parts by mass were added to the coating material for forming an undercoat layer prepared as described above. (Method for producing a coating material for forming a back layer)

[0260] A coating material for forming a back layer was prepared as follows. A coating material for forming a back layer was prepared by mixing the following raw materials in a stirred tank equipped with a dispersion device and subjecting them to a filter treatment. Carbon black (manufactured by ASAHI CARBON CO., LTD., trade name: #80): 100 parts by mass Polyester polyurethane: 100 parts by mass (manufactured by Nippon Polyurethane Industry Co., Ltd., product name: N-2304) Methyl ethyl ketone: 500 parts by mass Toluene: 400 parts by mass Cyclohexanone: 100 parts by mass Polyisocyanate (trade name: Coronat L, manufactured by TOSOH CORPORATION): 10 parts by mass (separation process)

[0261] Using the coating material prepared as described above, a magnetic tape having a medium configuration as shown below in Table 1 was prepared as described below. [Table 1]

[0262] First, a PEN film (base film) with an elongated shape and an average thickness of 4.0 μm was prepared as a support. Next, a coating material for forming an undercoat layer was applied to one major surface of the PEN film and dried to form an undercoat layer with an average thickness of 0.9 μm on one major surface of the PEN film. Next, a coating material for forming a magnetic layer was applied to the undercoat layer and dried to form a magnetic layer with an average thickness of 80 nm on the undercoat layer. Note that when the coating material for forming a magnetic layer is dried, the magnetic field of the magnetic powder is oriented in the thickness direction of the PEN film by a magnetic coil.Specifically, the magnetic field of the magnetic powder was aligned once in the running direction (longitudinal direction) of the PEN film by the magnetic coil and then in the thickness direction of the PEN film. Furthermore, the drying conditions (drying temperature and drying time) of the coating material to form a magnetic layer were adjusted, and the coercive force Hc1 in the perpendicular direction was adjusted as shown in Table 2.

[0263] Subsequently, a back layer with an average thickness of 0.3 µm was formed by applying a back layer coating material to the other major surface of the PEN film on which the undercoat layer and the magnetic layer were formed, and drying it. Then, the PEN film on which the undercoat layer, the magnetic layer, and the back layer were formed was cured. Afterward, it was calendered to smooth the surface of the magnetic layer. (cutting process)

[0264] The magnetic tape obtained as described above was cut to a width of 12.65 mm (1 / 2 inch). As a result, a magnetic tape having an elongated shape and an average thickness of 5.3 µm was obtained. As shown in Table 2, the thermal stability of the obtained magnetic tape was K u V act / k B T 77 and the ratio Hrp / Hc1 of the remaining coercive force Hrp to the coercive force Hc1 of the magnetic recording medium in the perpendicular direction was 1.78. (Writing the servo signal and data signal)

[0265] A servo signal and a data signal were written onto the elongated magnetic tape obtained as described above in the following manner. First, five servo tapes with a servo bandwidth W SBof 96 µm by writing a servo signal onto the magnetic tape using a servo recorder.

[0266] It should be noted that by writing servo signals, columns of inverted V-shaped magnetic patterns were formed on the servo tapes.

[0267] Next, a data signal was written onto the data tape between servo bands using a recording / reproducing device. At this time, the recording / reproducing device was controlled so that the recording track width W was 2.9 µm and the recording wavelength λ was a single recording wavelength of 0.208 µm. Note that the recording wavelength λ[nm] of the data signal was four times the minimum value L[nm] (= 0.052 µm) of the magnetization reversal pitch when recording at the shortest recording wavelength (i.e., the shortest recording wavelength L'=2×L, where the recording wavelength λ = (twice as long as L')). A ring-type head with a gap length of 0.2 µm was used as the recording head.

[0268] Here, the reason why the recording wavelength λ is twice the shortest recording wavelength L' is as follows. Namely, in the recording and reproducing system that uses a short wavelength, the output / noise ratio in recording and reproducing with the recording wavelength twice the shortest recording wavelength is generally often used. Furthermore, the SNR at twice the recording wavelength has a stronger correlation with the error rate than the SNR at the shortest recording wavelength. Furthermore, in the case where the SNR measurement is performed at the shortest recording wavelength, the tape noise is hidden in the system noise of the recording and reproducing system depending on the wavelength characteristics of the recording and reproducing system, and the noise characteristics of the medium are not accurately reflected in some cases.Especially in the case of high line density recording, the noise characteristics of the medium are often not reproduced correctly. The minimum value L of the

[0269] The magnetization reversal pitch and the data track width W were obtained as follows. First, the surface of the magnetic layer 13 was observed using a magnetic force microscope (MFM) to take an MFM image. Part A and Part B of Fig.13 each shows an example of the MFM image. Next, the dimension of the magnetization pattern column in the width direction of the magnetic tape was measured from the acquired MFM image and used as the track width W[nm]. Further, the distance between a bright part and a bright part in the longitudinal direction of the magnetic tape or the distance between a dark part and a dark part was defined as λ[nm]. After that, the value of half of λ[nm] was defined as L'[nm], and the value of half of L'[nm] was defined as L[nm]. [Example 2]

[0270] A magnetic tape was obtained in the same manner as in Example 1, except that the magnetic tape was prepared without alignment (i.e., the above-mentioned magnetic field alignment by the magnetic coil is not performed; the same applies hereinafter). The obtained magnetic tape had the coercive force Hc1, the residual coercive force Hrp, and the thermal stability K u V act / k BT, as shown in Table 2. [Example 3]

[0271] A magnetic tape was obtained in the same manner as in Example 1 except that the average particle volume of the magnetic powder was further increased to 1200 nm 3 was refined and the magnetic tape was produced without orientation. The resulting magnetic tape had the coercive force Hc1, the residual coercive force Hrp and the thermal stability K u V act / k B T, as shown in Table 2. [Example 4]

[0272] A magnetic tape was obtained in the same manner as in Example 1 except that the magnetic powder used in Example 3 was used. The obtained magnetic tape had the coercive force Hc1, the residual coercive force Hrp and the thermal stability K u V act / k B T, as shown in Table 2. [Comparison example 1]

[0273] A magnetic tape was obtained in the same manner as in Example 1 except that a magnetic powder having the average particle volume of 2500 nm 3 was used and the magnetic tape was produced without alignment. The resulting magnetic tape had the coercive force Hc1, the residual coercive force Hrp and the thermal stability K u V act / k B T, as shown in Table 2. [Comparison example 2]

[0274] A magnetic tape was obtained in the same manner as in Example 1, except that a magnetic powder with a lower Hc1 was used and the magnetic tape was prepared without orientation. The obtained magnetic tape had the coercive force Hc1, the residual coercive force Hrp, and the thermal stability K u V act / k B T, as shown in Table 2.

[0275] The signal attenuation amount SD and the electromagnetic conversion characteristics (SNR) were evaluated for the magnetic tapes according to Examples 1 to 4 and Comparative Examples 1 and 2 obtained as described above. These evaluation methods are described below. (Signal attenuation amount SD after 100 s)

[0276] For the samples in Examples and Comparative Examples, the signal attenuation amount SD after 100 s of elapsed time was obtained as follows. Specifically, a "Tape Head Tester" (hereinafter referred to as THTs) manufactured by MicroPhysics, Inc. was used. As the recording / reproducing head, the head mounted on the tape drive "TS1140" of IBM Corporation was used as is. At the time of measurement, a magnetic tape as a magnetic recording medium was cut into a length of 90 cm to form a ring so that the recording layer of the magnetic tape was on the back side, and then both ends of the magnetic tape were bonded together by an adhesive tape on the back of the magnetic tape. Further, a silver tape for detecting the tape circumferential position was attached adjacent to the bonded portion. The ring-shaped magnetic tape was attached to the THT and then rotated at a speed of 2 m / s.

[0277] Then, the 10 MHz signal generated using the "ARBITRARY WAVEFORM GENERATOR AWG2021" signal generator manufactured by TEKTRONIX, INC., was recorded for an amount equivalent to only one lap of the total tape length using the optimal recording current for the magnetic tape. After recording, the signals recorded on the tape were continuously played back from the next cycle, and the playback output was measured using a spectrum analyzer "8591E2" manufactured by Hewlett-Packard Company.

[0278] It should be noted that the spectrum analyzer settings at this time were as follows: RBW: 1 MHz, VBW: 1 MHz, SWP: 500 ms, Dot: 400, and a zero span mode. The measurement was performed for only 0.4 seconds on the "recording section", excluding the "surroundings of the band-bound section" where sufficient recording was not performed, and the average value Y of the playback output during this period was calculated. The measurement was performed for each lap of the band, and the average value Y of the playback output in each lap was used as the average value of the playback output Y(t) in the elapsed time since the end of signal recording (t=0). The measurement was performed until t=100 s and timely transferred to the connected PC and recorded.

[0279] The above-mentioned measurement procedure was performed four times using the same magnetic tape and the Y(t) values obtained by the respective measurements were averaged for the same elapsed time t to obtain a numerical sequence of Y ave (t). The resulting Y ave (t) and the elapsed time t were plotted on the Y-axis and X-axis, respectively, and an approximate curve was constructed from this graph using a logarithmic approximation. The obtained approximate curve was used to calculate the signal attenuation amount SD after 100 s. The calculation results are shown in Table 2 below. (SNR in an environment of 25 °C)

[0280] Using a 1 / 2-inch tape transport device (MTS Transport, manufactured by Mountain Engineering II) mounted with a recording / playback head and a recording / playback amplifier, the SNR (electromagnetic conversion characteristics) of the magnetic tape was measured in an environment of 25°C. A ring-type head with a gap length of 0.2 µm was used as the recording head, and a GMR head with a pitch between shields of 0.1 µm was used as the playback head. The relative speed was set to 6 m / s and the recording clock frequency to 160 MHz.

[0281] Furthermore, the SNR was calculated based on the method described in the following document (measurement method using a spectrum analyzer). The results are shown in Table 2 below as relative values, where the SNR in Comparative Example 1 is defined as 0 dB.

[0282] Y. Okazaki: “An Error Rate Emulation System”, IEEE Trans. Man., 31, pp. 3093-3095 (1995)

[0283] Table 2 below shows the results of the evaluation of the magnetic tapes according to Examples 1 to 4 and Comparative Examples 1 and 2. (Table 2)

[0284] The following can be seen from Table 2.

[0285] All magnetic tapes according to Examples 1 to 4 had a signal attenuation amount SD of less than -0.30 dB after 100 seconds, although the average particle volume of the magnetic powder was 2000 nm 3or less. For this reason, all of the magnetic tapes according to Examples 1 to 4 were excellent in preservation stability even though the average particle volume of the magnetic powder was small. In addition, all of the magnetic tapes according to Examples 1 to 4 had an SNR of 0.5 dB or more and excellent electromagnetic conversion characteristics. From these results, it is apparent that the magnetic recording medium according to the present disclosure has excellent preservation stability and also excellent electromagnetic conversion characteristics even though the average particle volume of the magnetic powder is small.

[0286] The magnetic tapes according to Examples 3 and 4 exhibit excellent preservation stability and electromagnetic conversion properties even though they contain the magnetic powder having an average particle volume smaller than that of the magnetic tape according to Examples 1 and 2. The magnetic tape according to Example 4 exhibits better preservation stability and electromagnetic conversion properties than the magnetic tape according to Example 3. For this reason, it can be seen that the effects of the present disclosure can be obtained even in the case where magnetic powder having a small average particle volume (e.g., 1500 nm 3 or less) as in Examples 3 and 4. Therefore, according to the present disclosure, it is possible to improve the recording density in addition to the preservation stability and the electromagnetic conversion properties.

[0287] From the comparison between Comparative Examples 1 and 2, it is clear that the signal attenuation amount SD increases as the average particle volume of the magnetic powder decreases. From the comparison between Comparative Example 2 and Examples 1 and 2, it is then clear that the signal attenuation amount SD can be reduced by setting Hrp / Hc1 to, for example, 2.10 or less, particularly 2.05 or less, and particularly 2.00 or less, even when the average particle volume of the magnetic powder is similarly low. Furthermore, it is assumed that the thermal stability K u V act / k B T of 60 or more contributes to reducing the signal attenuation amount SD.

[0288] Furthermore, it is also apparent from the comparison between Comparative Example 2 and Examples 1 and 2 that the SNR is improved by setting Hrp / Hc1 to, for example, 2.10 or less, particularly 2.05 or less, and particularly 2.00 or less. Furthermore, it is also assumed that the thermal stability K u V act / k B T of 60 or more contributes to the improvement of the SNR. As can be seen from the results of Examples 3 and 4, this improvement is also evident in the case where the average particle volume of the magnetic powder is small (e.g., 1500 nm 3 or less).

[0289] From Examples 1 to 4, it can be seen that even in the case where the average particle volume of the magnetic powder is reduced to a smaller value (e.g., 1500 nm 3or less), the signal attenuation amount SD can be reduced by setting Hrp / Hc1 to, for example, 2.10 or less, particularly 2.05 or less, and particularly 2.00 or less. Furthermore, it is assumed that the thermal stability K u V act / k B T of 60 or more contributes to reducing the signal attenuation amount SD.

[0290] Although embodiments of the present disclosure and examples have been specifically described above, the present disclosure is not limited to the above-described embodiments and examples, and various modifications based on the technical idea of the present disclosure may be made.

[0291] For example, the configurations, methods, processes, shapes, materials, numerical values, and the like described in the above-mentioned embodiments and examples are merely examples, and other configurations, methods, processes, shapes, materials, numerical values, and the like can be used as needed. Furthermore, the chemical formulas of compounds and the like are representative, and the valences and the like are not limited as long as they represent common names of the same compound.

[0292] The above-mentioned configurations, methods, processes, shapes, materials, numerical values, and the like in the embodiments and examples can be combined with each other without departing from the gist of the present disclosure.

[0293] Furthermore, the numerical range indicated by using "to" in the present specification indicates a range including numerical values described before and after "to" as the minimum value and maximum value, respectively. In the numerical range described step by step in the present specification, the upper limit or lower limit of the numerical range in one step may be replaced by the upper limit or lower limit of the numerical range in another step. Unless otherwise specified, one of the materials exemplified in the present specification may be used alone, or two or more of them may be used in combination.

[0294] It should be noted that the present disclosure may also assume the following configurations.

[0295] [1] A tape-shaped magnetic recording medium comprising: a base; and a magnetic layer provided on the base and containing a magnetic powder, wherein an average particle volume V of the magnetic powder 2000 nm 3 or less, an average thickness of the magnetic recording medium is 5.3 µm or less, a thermal stability K u V act / k B T of the magnetic recording medium is 60 or more and a ratio Hrp / Hc1 of a residual coercive force Hrp of the magnetic recording medium, measured using a pulsed magnetic field, to a coercive force Hc1 of the magnetic recording medium in the perpendicular direction is 2.10 or less.

[0296] [2] Magnetic recording medium according to [1], wherein the average particle volume V of the magnetic powder 1800 nm 3 or less.

[0297] [3] Magnetic recording medium according to [1], wherein the average particle volume V of the magnetic powder 1600 nm 3 or less.

[0298] [4] The magnetic recording medium according to any one of [1] to [3], wherein the thermal stability K u V act / k B T is 63 or more.

[0299] [5] The magnetic recording medium according to any one of [1] to [3], wherein the thermal stability K u V act / k B T is 65 or more.

[0300] [6] A magnetic recording medium according to any one of [1] to [5], wherein the ratio Hrp / Hc1 is 2.05 or less.

[0301] [7] A magnetic recording medium according to any one of [1] to [5], wherein the ratio Hrp / Hc1 is 2.00 or less.

[0302] [8] Magnetic recording medium according to any one of [1] to [7], wherein the magnetic powder contains hexagonal ferrite.

[0303] [9] Magnetic recording medium according to [8], wherein the hexagonal ferrite contains Ba, Sr and / or Ca.

[0304]

[10] Magnetic recording medium according to any one of [1] to [9], wherein a signal attenuation amount SD of the magnetic recording medium 100 seconds after recording satisfies the following relationship: -0.30 dB ≤ SD.

[0305]

[11] Magnetic recording medium according to any one of [1] to [9], wherein the signal attenuation amount SD of the magnetic recording medium 100 seconds after recording satisfies the following relationship: -0.25 dB ≤ SD.

[0306]

[12] The magnetic recording medium according to any one of [1] to

[11] , wherein a thickness t m the magnetic layer satisfies the following relationship: 30 nm ≤ t m ≤ 90 nm.

[0307]

[13] The magnetic recording medium according to any one of [1] to

[12] , wherein the coercive force Hc1 is 500 Oe or more.

[0308]

[14] The magnetic recording medium according to any one of [1] to

[13] , wherein an average thickness of the base is 4.2 µm or less.

[0309]

[15] Magnetic recording medium according to any one of [1] to

[14] , wherein an underlayer is provided between the magnetic layer and the base and an average thickness of the underlayer is 2.0 µm or less.

[0310]

[16] Magnetic recording medium according to any one of [1] to

[15] , wherein of two surfaces of the base, a back layer is provided on a surface opposite to a surface on which the magnetic layer is provided, and an average thickness of the back layer is 0.6 µm or less.

[0311]

[17] A magnetic recording medium according to any one of [1] to

[16] , wherein an average particle size of the magnetic powder is 50 nm or less.

[0312]

[18] Tape cassette comprising: the tape-shaped magnetic recording medium according to any one of [1] to

[17] ; a communication unit that communicates with a recording / reproducing device; a storage unit; and a control unit that stores in the storage unit information received from the recording / reproducing device via the communication unit, and reads the information from the storage unit and transmits the read information to the recording / reproducing device via the communication unit in response to a request from the recording / reproducing device, wherein the information includes adjustment information for adjusting the tension applied to the magnetic recording medium in the longitudinal direction. List of reference symbols 10 Magnetic recording medium 11 Base (base layer) 12 Lower class 13 Magnetic layer 14 Back layer

Claims

[1] A tape-shaped magnetic recording medium (10) comprising: a base (11); and a magnetic layer (13) provided on the base (11) and containing a magnetic powder, wherein an average particle volume V of the magnetic powder 2000 nm 3 or less, an average thickness of the magnetic recording medium is 5.3 µm or less, a thermal stability K u V act / k B T of the magnetic recording medium is 60 or more and a ratio Hrp / Hc1 of a residual coercive force Hrp of the magnetic recording medium (10) measured using a pulsed magnetic field to a coercive force Hc1 of the magnetic recording medium (10) in the perpendicular direction is 2.10 or less. [2] The magnetic recording medium (10) according to claim 1, wherein the average particle volume V of the magnetic powder is 1800 nm 3 or less. [3] The magnetic recording medium (10) according to claim 1, wherein the average particle volume V of the magnetic powder is 1600 nm 3 or less. [4] Magnetic recording medium (10) according to claim 1, wherein the thermal stability K u V act / k B T is 63 or more. [5] Magnetic recording medium (10) according to claim 1, wherein the thermal stability K u V act / k B T is 65 or more. [6] The magnetic recording medium (10) according to claim 1, wherein the ratio Hrp / Hc1 is 2.05 or less. [7] The magnetic recording medium (10) according to claim 1, wherein the ratio Hrp / Hc1 is 2.00 or less. [8] The magnetic recording medium (10) according to claim 1, wherein the magnetic powder contains hexagonal ferrite. [9] The magnetic recording medium (10) according to claim 8, wherein the hexagonal ferrite contains Ba, Sr and / or Ca. [10] The magnetic recording medium (10) according to claim 1, wherein a signal attenuation amount SD of the magnetic recording medium (10) 100 seconds after recording satisfies the following relationship: -0.30 dB ≤ SD. [11] The magnetic recording medium (10) according to claim 1, wherein the signal attenuation amount SD of the magnetic recording medium (10) 100 seconds after recording satisfies the following relationship: -0.25 dB ≤ SD. [12] Magnetic recording medium (10) according to claim 1, wherein a thickness t m the magnetic layer (13) satisfies the following relationship: 30 nm ≤ t m ≤ 90 nm. [13] The magnetic recording medium (10) according to claim 1, wherein the coercive force Hc1 is 500 Oe or more. [14] The magnetic recording medium (10) according to claim 1, wherein an average thickness of the base (11) is 4.2 µm or less. [15] Magnetic recording medium (10) according to claim 1, wherein a sub-layer (12) is provided between the magnetic layer (13) and the base (11) and an average thickness of the underlayer (12) is 2.0 µm or less. [16] Magnetic recording medium (10) according to claim 1, wherein of two surfaces of the base (11), a back layer (14) is provided on a surface opposite to a surface on which the magnetic layer (13) is provided, and an average thickness of the rear layer (14) is 0.6 µm or less. [17] The magnetic recording medium (10) according to claim 1, wherein an average particle size of the magnetic powder is 50 nm or less. [18] Tape cassette (10A) comprising: the tape-shaped magnetic recording medium (10) according to claim 1; a communication unit (331) communicating with a recording / reproducing device (30); a storage unit (336); and a control unit (335) which stores in the storage unit (336) information received from the recording / reproducing device (30) via the communication unit (331), and reads the information from the storage unit (336) and transmits the read information to the recording / reproducing device (30) via the communication unit (331) in response to a request from the recording / reproducing device (30), wherein the information comprises adjustment information for adjusting the tension applied to the magnetic recording medium (10) in the longitudinal direction.

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