Magnetic Recording Media

Abstract

To provide a magnetic recording medium capable of obtaining high output, having excellent thermal stability, and obtaining ease of recording.SOLUTION: A magnetic recording medium 30 includes a recording layer 33 containing magnetic powder. The magnetic powder includes magnetic particles including particles containing ε-iron oxide and iron oxide provided on at least a part of a surface of the particle. A ratio R1 (=(σ / D)×100) of a standard deviation σ of a particle size distribution of the magnetic particle to an average particle diameter D of the magnetic particle is R1≤40%.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to magnetic recording media. [Background technology]

[0002] Conventionally, coating-type magnetic recording media have been known as magnetic recording media, in which a recording layer is formed by coating a non-magnetic support with a magnetic paint containing a magnetic powder, a binder, and an organic solvent, and then drying the coating-type magnetic recording media. Such coating-type magnetic recording media are widely used as high-density recording media, such as backup data cartridges.

[0003] In recent years, the magnetic powder contained in the recording layer has been made finer in order to accommodate recording media with high recording densities, but as the magnetic powder is further made finer, it is subject to the effects of external heat in the magnetic tape usage environment, and the effects of so-called thermal disturbance of magnetization become more pronounced, resulting in the phenomenon of recorded magnetization disappearing. In order to avoid the effects of this thermal disturbance of magnetization, it is necessary to increase the coercive force of the magnetic powder.

[0004] However, as the coercive force is increased, it becomes difficult to cause magnetization reversal by a recording head, i.e., to record information signals. Also, as the fine particles are made finer, the saturation magnetization amount σ s This, combined with the reduction in output due to high density recording, can result in a significant deterioration in the signal-to-noise ratio (hereinafter referred to as "CNR").

[0005] To solve these problems, for example, Patent Document 1 proposes a method for producing a magnetic powder in which the surfaces of ε-iron oxide particles are subjected to a reduction treatment to form a shell portion containing α-Fe. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2016 / 092744 Brochure Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present technology is to provide a magnetic recording medium that is capable of obtaining high output, has excellent thermal stability, and allows ease of recording. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, a first aspect of the present disclosure provides a recording layer including a magnetic powder, the magnetic powder including magnetic particles including particles including ε-iron oxide and iron oxide provided on at least a portion of the surface of the particle, The iron oxide includes iron tetraoxide or gamma-iron oxide. The magnetic recording medium has a ratio R1 (=(σ / D)×100) of the standard deviation σ of the particle size distribution of the magnetic particles to the average particle diameter D of the magnetic particles, which satisfies R1≦40%. A second aspect of the present disclosure is a method for producing a magnetic powder, which comprises reducing particles containing ε-iron oxide (including those in which part of the Fe sites are substituted with a metal element) to form triiron tetroxide (including those in which part of the Fe sites are substituted with a metal element) on at least a part of the surface of the particles to obtain magnetic particles, wherein the ratio R1 (=(σ / D)×100) of the standard deviation σ of the particle size distribution of the magnetic particles to the average particle diameter D of the magnetic particles is R1≦40%.

[0009] A third aspect of the present disclosure includes obtaining magnetic particles by subjecting particles containing ε-iron oxide (including those in which a portion of the Fe site is substituted with a metal element) to a reduction treatment to form triiron tetroxide (including those in which a portion of the Fe site is substituted with a metal element) on at least a portion of the surface of the particles, the magnetic particles having a core-shell structure, and an average volume V of the shell portion of the magnetic particles. s But 90 nm 3 ≦V s and the average volume of the shell V is the average volume of the magnetic particles V s The proportion of R2(=(V s / V) × 100) is 16%≦R2≦62%.

[0010] A fourth aspect of the present disclosure includes obtaining magnetic particles by subjecting particles containing ε-iron oxide (including those in which a portion of the Fe site is substituted with a metal element) to a reduction treatment to form triiron tetroxide (including those in which a portion of the Fe site is substituted with a metal element) on at least a portion of the surface of the particles, and obtaining a saturation magnetization σ s However, 30 emu / g≦σ s A method for producing magnetic powder with a molecular weight of ≦60 emu / g.

[0011] A fifth aspect of the present disclosure is a method for producing a magnetic powder, comprising transforming first particles containing ferrous oxide (including those in which a portion of the Fe sites is substituted with the metal element M) by firing into second particles containing γ-iron oxide (including those in which a portion of the Fe sites is substituted with the metal element M), and then transforming a portion of the second particles into ε-iron oxide (including those in which a portion of the Fe sites is substituted with the metal element M), thereby obtaining magnetic particles.

[0012] A sixth aspect of the present disclosure is a magnetic recording medium comprising a recording layer containing magnetic powder, the magnetic powder comprising magnetic particles including particles containing ε-iron oxide (including those in which a portion of the Fe site is substituted with a metal element) and triiron tetroxide (including those in which a portion of the Fe site is substituted with a metal element) provided on at least a portion of the surface of the particle.

[0013] A seventh aspect of the present disclosure is a magnetic recording medium comprising a recording layer containing magnetic powder, the magnetic powder comprising magnetic particles comprising particles containing ε-iron oxide (including those in which part of the Fe site is substituted with a metal element) and γ-iron oxide (including those in which part of the Fe site is substituted with a metal element) provided on at least a portion of the surface of the particle. An eighth aspect of the present disclosure is a recording layer including a magnetic powder, the magnetic powder including magnetic particles having particles including ε-iron oxide and iron oxide provided on at least a portion of the surface of the particle, and a ratio R of a standard deviation σ of a particle size distribution of the magnetic particles to an average particle diameter D of the magnetic particles. 1 (=(σ / D)×100) is R 1 ≦40%, and the saturation magnetization M s However, 50 emu / cc≦M s A magnetic recording medium having a density of ≦110 emu / cc. A ninth aspect of the present disclosure is a recording layer including a magnetic powder, the magnetic powder including magnetic particles having particles including ε-iron oxide and iron oxide provided on at least a portion of the surface of the particle, and a ratio R of a standard deviation σ of a particle size distribution of the magnetic particles to an average particle diameter D of the magnetic particles. 1 (=(σ / D)×100) is R 1 ≦40%, and the coercive force H c is 3000 Oe or less. Effect of the Invention

[0014] According to the present disclosure, it is possible to obtain high output, excellent thermal stability, and ease of recording. Note that the effects described here are not necessarily limited, and may be any of the effects described in the present disclosure or effects different from those effects. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a cross-sectional view of a magnetic powder according to the first embodiment of the present disclosure. [Diagram 2] FIG. 4 is a cross-sectional view of a magnetic powder according to a second embodiment of the present disclosure. [Diagram 3] FIG. 11 is a cross-sectional view of a magnetic recording medium according to a third embodiment of the present disclosure. [Figure 4] FIG. 2 is a process diagram illustrating the method for producing the magnetic powder according to Examples 1 to 8 and 11 to 15. [Diagram 5] FIG. 11 is a process diagram for explaining the method for producing the magnetic powder according to Examples 9 and 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The embodiments of the present disclosure will be described in the following order. 1 First embodiment (example of magnetic powder) 2. Second embodiment (example of magnetic powder) 3. Third embodiment (example of magnetic recording medium)

[0017] <1 First embodiment> [Magnetic powder composition] The magnetic powder according to the first embodiment of the present disclosure includes magnetic particles 10 having a core-shell structure, as shown in FIG. 1. The magnetic particles 10 include a core portion 11 including ε-iron oxide (including those in which a part of the Fe site is substituted with a metal element M) and a shell portion 12 provided around the core portion 11 and including triiron tetroxide (including those in which a part of the Fe site is substituted with a metal element M). The core portion 11 and the shell portion 12 are preferably exchange-coupled. At the interface between the core portion 11 and the shell portion 12, the composition and / or state of both may change discontinuously or may change continuously. The magnetic particles 10 have, for example, an approximately cubic or approximately spherical shape. The magnetic powder according to the first embodiment is suitable for use in the recording layer (magnetic layer) of a high-density magnetic recording medium.

[0018] (average particle radius r) The average particle radius r of the magnetic particles 10 is preferably 4 nm≦r≦20 nm. When the average particle radius r of the magnetic particles 10 is 4 nm≦r, the decrease in dispersibility of the magnetic powder can be suppressed when preparing a coating material for forming a recording layer using the magnetic powder, and the electromagnetic conversion characteristics (e.g., CNR) of the magnetic recording medium can be further improved. On the other hand, when the average particle radius r of the magnetic particles 10 is r≦20 nm, the increase in noise of the magnetic recording medium can be suppressed when preparing a recording layer using the magnetic powder. Therefore, the electromagnetic conversion characteristics (e.g., CNR) of the magnetic recording medium can be further improved. In addition, when a coating material for forming a recording layer containing the magnetic powder is applied to form a coating film, the deterioration of the surface properties of the coating film can be suppressed. In this disclosure, the average particle radius r and the average particle diameter D of the magnetic particles 10 are referred to not only when the magnetic particles 10 have an almost spherical shape, but also when they have an almost cubic shape.

[0019] The average particle radius r of the magnetic particles 10 is determined as follows. First, the magnetic powder is photographed using a transmission electron microscope (TEM). The device (TEM) used for the photographing and the photographing conditions are shown below. Equipment (TEM): Hitachi H9000NAR Acceleration voltage: 200 kV Total magnification: 500,000x Next, 500 magnetic particles 10 whose particle shapes can be clearly confirmed are randomly selected from the TEM photographs, and the area S of each of these magnetic particles 10 is calculated. Next, assuming that the shape of the magnetic particles 10 is spherical, the radius r of each magnetic particle 10 is calculated from the following formula: A is calculated to obtain the particle size distribution of the magnetic powder. r A =(S / π) 1 / 2 Next, the median diameter (50% diameter, D50) is calculated from the particle size distribution, and this is set as the average particle radius r.

[0020] (Ratio R1 of standard deviation σ of particle size distribution to average particle diameter D) It is preferable that the ratio R1 (=(σ / D)×100) of the standard deviation σ of the particle size distribution of the magnetic particles 10 to the average particle diameter D of the magnetic particles 10 is R1≦40%. When the ratio R1 is R1≦40%, the variation in particle size of the magnetic particles 10 is small, and the variation in the magnetic properties of the magnetic powder can be suppressed. The lower limit of the ratio R1 is not particularly limited, but is, for example, 5%≦R1.

[0021] The above ratio R1 is calculated as follows. First, the area S of each particle is calculated in the same manner as the average particle radius r of the magnetic particles 10. Next, assuming that the shape of the magnetic particles 10 is spherical, the diameter D of each particle is calculated from the following formula: A is calculated to obtain the particle size distribution of the magnetic powder. D A =2×(S / π) 1 / 2 Next, the median diameter (50% diameter, D50) is calculated from the obtained particle size distribution, and this is set as the average particle diameter D. In addition, the standard deviation σ is calculated from the obtained particle size distribution. Next, the ratio R1 (=(σ / D)×100) is calculated using the obtained average particle diameter D and the standard deviation σ of the particle size distribution.

[0022] (Saturation magnetization amount σ s ) Saturation magnetization amount σ of magnetic particle 10s However, 30 emu / g≦σ s It is preferable that the saturation magnetization is ≦60 emu / g. s 30 emu / g≦σ s When a recording layer is produced using the magnetic powder, a higher output can be obtained, and therefore better electromagnetic conversion characteristics (e.g., CNR) can be obtained. s is σ s When it is ≦60 emu / g, the ratio of shell portion 12 to core portion 11, that is, the ratio of soft magnetic material to hard magnetic material, can be prevented from becoming too high, and therefore a decrease in coercive force Hc can be prevented.

[0023] The above saturation magnetization amount σ s can be obtained as follows. First, a magnetic powder sample of a predetermined shape is prepared. The magnetic powder sample can be prepared freely as long as it does not affect the measurement, such as by compacting it into a measurement capsule or attaching it to a measurement tape. Next, an MH loop is obtained for the magnetic powder sample using a vibrating sample magnetometer (VSM), and then the saturation magnetization σ is calculated from the obtained MH loop. s is calculated. The above MH loop measurement is performed in an environment of 25°C. A high-sensitivity vibration sample magnetometer "VSM-P7-15 type" manufactured by Toei Industry Co., Ltd. is used to measure the above MH loop. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, number of MH averages: 20.

[0024] (Core) The core 11 is preferably made of ε-Fe2O3 crystal (including those in which a part of the Fe site is replaced with the metal element M) which is a hard magnetic material as a main phase, and more preferably made of single-phase ε-Fe2O3 crystal. The metal element M is, for example, at least one of Al, Ga, and In. However, when the molar ratio of M to Fe is expressed as M:Fe=x:(2-x), 0≦x<1. Here, the composition formula of ε-iron oxide is expressed as ε-Fe2O3, but ε-iron oxide may have a non-stoichiometric composition.

[0025] In this disclosure, unless otherwise specified, the ε-Fe2O3 crystal includes not only pure ε-Fe2O3 crystal in which the Fe sites are not substituted with other elements, but also crystals in which a part of the Fe sites is substituted with a trivalent metal element M and which have the same space group as the pure ε-Fe2O3 crystal (i.e., the space group is Pna21).

[0026] (Shell part) The shell portion 12 covers at least a part of the periphery of the core portion 11. Specifically, the shell portion 12 may cover a part of the periphery of the core portion 11, or may cover the entire periphery of the core portion 11. From the viewpoint of ensuring sufficient exchange coupling between the core portion 11 and the shell portion 12 and improving magnetic properties, it is preferable that the shell portion 12 covers the entire surface of the core portion 11.

[0027] The shell portion 12 is preferably made of Fe3O4 crystal (including those in which a part of the Fe site is replaced with the metal element M) which is a soft magnetic material as the main phase, and more preferably made of single-phase Fe3O4 crystal. However, when the molar ratio of M to Fe is expressed as M:Fe=x:(3-x), 0≦x<1.5. Here, the composition formula of triiron tetroxide is expressed as Fe3O4, but triiron tetroxide may have a non-stoichiometric composition.

[0028] In this disclosure, unless otherwise specified, the Fe3O4 crystal includes not only pure Fe3O4 crystal in which the Fe sites are not substituted with other elements, but also crystal in which a portion of the Fe sites is substituted with a trivalent metal element M and which has the same space group as the pure Fe3O4 crystal.

[0029] The shell portion 12 can be obtained, for example, by reducing the surface of a particle containing ε-iron oxide (hard magnetic particle) that is a precursor particle of the magnetic particle 10.

[0030] (The average volume of the shell V s , the average volume of the shell V relative to the average volume V of the magnetic particles s Ratio of Average volume V of shell 12 s But 90 nm 3 ≦V2, and the average volume V of the shell portion 12 relative to the average volume V of the magnetic particles 10 s The proportion of R2(=(V s / V)×100) is preferably 16%≦R2≦62%. s is 90 nm 3 ≦V s If the ratio R2 is 16% or less, the saturation magnetization σ s becomes too small, for example, the saturation magnetization σ s 30emu / g≦σ s Therefore, when a recording layer is produced using the magnetic powder, a higher output can be obtained, and therefore better electromagnetic conversion characteristics (e.g., CNR) can be obtained. On the other hand, the average volume V s is 90 nm 3 ≦V2 and the ratio R2 is R2≦62%, the saturation magnetization σ s is suppressed from becoming too large, for example, the saturation magnetization σ s σ s ≦60 emu / g. In addition, the ratio of the shell portion 12 to the core portion 11, i.e., the ratio of the soft magnetic material to the hard magnetic material, can be prevented from becoming too high, so that a decrease in the coercive force Hc can be suppressed.

[0031] The above average volume V s The ratio R2 is calculated as follows: First, the magnetic powder is photographed using a TEM. The equipment (TEM) and photographing conditions used for the photographing are shown below. Equipment (TEM): Hitachi H9000NAR Acceleration voltage: 200 kV Total magnification: 500,000x Next, 500 magnetic particles 10 whose particle shapes could be clearly confirmed were randomly selected from the TEM photographs taken, and the area S of each of the magnetic particles 10 and the area S of the core portion 11 were measured. h Next, assuming that the magnetic particles 10 and the core portion 11 are spherical, the radius r of each magnetic particle 10 is calculated from the following formula: A and the radius r of each core portion 11 Ah is calculated to obtain the particle distribution of the magnetic particles 10 and the core portions 11. r A =(S / π) 1 / 2 r Ah =(S h / π) 1 / 2

[0032] Next, the median diameter (50% diameter, D50) is calculated from the particle distribution of the magnetic particles 10, and this is defined as the average particle radius r of the magnetic particles 10. In addition, the median diameter (50% diameter, D50) is calculated from the particle distribution of the core portion 11, and this is defined as the average radius r of the core portion 11. h Next, assuming that the magnetic particles 10 and the core portion 11 are spherical, the average volume V of the magnetic particles 10 and the average volume V of the core portion 11 are calculated from the following formula: h Request. V = (4 / 3) × π × r 3 V h =(4 / 3)×π×r h 3

[0033] Next, the average volume V of the magnetic particles 10 and the average volume V of the core portion 11 are calculated. h Using the above, the average volume V of the shell portion 12 is calculated from the following formula: s Request. V s =VV h Finally, the average volume V of the magnetic particles 10 and the average volume V of the shell portion 12 were calculated. s Using the above, the average volume V of the shell portion 12 relative to the average volume V of the magnetic particle 10 is calculated.s The proportion of R2(=(V s Calculate V( / V1) × 100).

[0034] [Magnetic powder manufacturing method] A method for producing a magnetic powder according to the first embodiment of the present disclosure will be described below. This method for producing a magnetic powder involves reducing particles (hereinafter referred to as "ε-iron oxide particles") containing ε-iron oxide (including those in which a portion of the Fe site is substituted with the metal element M) to form a shell portion 12 containing triiron tetroxide (including those in which a portion of the Fe site is substituted with the metal element M) on at least a portion of the surface of the ε-iron oxide particle, thereby obtaining magnetic particles 10 having a core-shell structure.

[0035] First, a powder of ε-iron oxide particles is prepared. The ε-iron oxide particles preferably have a main phase of ε-Fe2O3 crystals (including those in which a portion of the Fe site is substituted with a metal element M), and more preferably are made of a single phase of ε-Fe2O3.

[0036] Then, the material is transferred into a heating furnace, and the inside of the heating furnace is replaced with a neutral gas or an inert gas. As the neutral gas, for example, at least one gas selected from the group consisting of nitrogen (N2), dry hydrogen (dryH2), and ammonia (NH3) decomposition gas can be used. As the inert gas, for example, at least one gas selected from the group consisting of argon (Ar) and helium (He) can be used.

[0037] Next, the powder of ε-iron oxide particles is reduced by a gas-phase reduction method. More specifically, the powder of ε-iron oxide particles is heat-treated while a reducing gas is introduced into a heating furnace. As a result, a shell portion 12 containing Fe3O4 crystals (including those in which a part of the Fe site is substituted with a metal element M) is formed on at least a part of the surface of the ε-iron oxide particles. Examples of the reducing gas include hydrogen (H2), carbon monoxide (CO), and hydrocarbon gases (CH4, C3H8, C4H 10 At least one selected from the group consisting of

[0038] The heating time during the heat treatment is preferably 10 minutes to 1 hour when using a reducing gas with an H2 concentration of 4%. When the heating time is 10 minutes or more, the surroundings of ε-Fe2O3 can be effectively reduced to Fe3O4. On the other hand, when the heating time is 1 hour or less, the reduction to Fe3O4 can be effectively suppressed while the disappearance of ε-Fe2O3 is effectively suppressed.

[0039] The heating temperature during the heat treatment is preferably 250° C. or higher and 600° C. or lower. When the heating temperature is 250° C. or higher, ε-Fe2O3 can be effectively reduced to Fe3O4. On the other hand, when the heating temperature is 600° C. or lower, the transformation of ε-Fe2O3 into a different crystal due to heat can be effectively suppressed.

[0040] After that, the sintering furnace is cooled to room temperature, and the obtained magnetic powder is carried out from the heating furnace, thereby obtaining the magnetic powder containing the magnetic particles shown in FIG.

[0041] [effect] The magnetic powder according to the first embodiment includes magnetic particles 10 having a core portion 11 containing ε-iron oxide (including those in which a portion of the Fe site is substituted with a metal element) and a shell portion 12 containing triiron tetroxide (including those in which a portion of the Fe site is substituted with the metal element) provided at least partially around the core portion 11. By forming a recording layer of a magnetic recording medium using this magnetic powder, it is possible to realize a magnetic recording medium that has high output, excellent thermal stability, and ease of recording.

[0042] In the method for producing magnetic powder according to the first embodiment, the surfaces of previously prepared ε-iron oxide particles are directly subjected to reduction treatment, so that the particle diameter of the ε-iron oxide particles that serve as precursor particles is approximately the same as the particle diameter of the magnetic particles 10 obtained by reduction treatment. Therefore, by adjusting the particle diameter of the ε-iron oxide particles that serve as precursor particles, it is possible to prepare magnetic particles 10 having a desired particle diameter. This makes it possible to suppress the occurrence of variations in particle size distribution.

[0043] In the technology described in Patent Document 1, it is difficult for ε-iron oxide (hard magnetic material) and α-Fe (soft magnetic material) to coexist, and an oxide film is required on the surface, so the process is complicated and it is difficult to adjust a three-layer structure (a three-layer structure consisting of one core layer and two shell layers). Therefore, it is difficult to manufacture magnetic particles having a core-shell structure. In contrast, in the magnetic particles according to the first embodiment, oxidation-resistant triiron tetroxide (soft magnetic material) is formed on the surface of the ε-iron oxide particles (hard magnetic particles), so the process is simple and it is easy to adjust a two-layer structure (a two-layer structure consisting of one core layer and one shell layer). Therefore, magnetic particles 10 having a core-shell structure can be easily manufactured.

[0044] <2. Second embodiment> [Magnetic powder composition] The magnetic powder according to the second embodiment of the present disclosure includes magnetic particles 20 having a core-shell structure, as shown in Fig. 2. The magnetic particles 20 include a core portion 21 including ε-iron oxide (including iron oxide in which a portion of the Fe site is substituted with a metal element) and a shell portion 22 including γ-iron oxide (including iron oxide in which a portion of the Fe site is substituted with the metal element).

[0045] (Core) The core portion 21 can be obtained, for example, by transforming the inside of a particle containing γ-iron oxide (including those in which a part of the Fe site is substituted with the metal element) as a precursor particle of the magnetic particle 20 into ε-iron oxide. Except for the above-mentioned points, the core portion 21 is similar to the core portion 11 in the first embodiment.

[0046] (Shell part) The shell portion 22 is preferably made of a soft magnetic γ-Fe2O3 crystal (including those in which a part of the Fe site is replaced with the metal element M) as the main phase, and more preferably made of a single-phase γ-Fe2O3 crystal. However, when the molar ratio of M to Fe is expressed as M:Fe=x:(2-x), 0≦x<1. Here, the composition formula of γ-iron oxide is expressed as γ-Fe2O3, but γ-iron oxide may have a non-stoichiometric composition. The shell portion 12 can be obtained, for example, by transforming particles containing ferrous oxide (including those in which a part of the Fe site is replaced with the metal element M) as precursor particles through sintering.

[0047] In this disclosure, unless otherwise specified, the γ-Fe2O3 crystal includes a pure γ-Fe2O3 crystal in which the Fe site is not substituted with other elements, as well as a crystal in which a part of the Fe site is substituted with a trivalent metal element M and which has the same space group as the pure γ-Fe2O3 crystal. The shell portion 22 is similar to the shell portion 12 in the first embodiment except for the above points.

[0048] [Magnetic powder manufacturing method] A method for producing a magnetic powder according to a second embodiment of the present disclosure will now be described. In this method, particles containing ferrous oxide (including those in which a portion of the Fe site is substituted with a metal element) (hereinafter referred to as "FeO particles") are sintered to transform them into particles containing γ-iron oxide (including those in which a portion of the Fe site is substituted with a metal element) (hereinafter referred to as "γ-iron oxide particles"), and then the interior of the γ-iron oxide particles is transformed into ε-iron oxide to obtain magnetic particles 20 having a core-shell structure.

[0049] First, a powder of FeO particles is prepared. The FeO particles preferably have FeO crystals (including those in which a part of the Fe site is replaced with the metal element M) as the main phase, and more preferably are made of single-phase FeO crystals. However, when the molar ratio of M to Fe is expressed as M:Fe=x:(1-x), 0≦x<1. Here, the composition formula of ferrous oxide is expressed as FeO, but ferrous oxide may have a non-stoichiometric composition.

[0050] In the present disclosure, unless otherwise specified, the FeO crystal includes not only a pure FeO crystal in which the Fe sites are not substituted with other elements, but also a crystal in which a part of the Fe sites is substituted with a divalent metal element M and which has the same space group as the pure FeO crystal.

[0051] The FeO particle powder is then transported to a sintering furnace, the temperature of the sintering furnace is raised, the FeO particle powder is sintered, the FeO particles are transformed into γ-iron oxide particles, and the inside of the γ-iron oxide particles is transformed into ε-iron oxide. The γ-iron oxide particles are preferably those having a γ-Fe2O3 crystal (including those in which a part of the Fe site is substituted with the metal element M) as the main phase, and more preferably those made of single-phase Fe3O4. The ε-iron oxide contained in the inside of the γ-iron oxide particles is preferably those having a ε-Fe2O3 crystal (including those in which a part of the Fe site is substituted with the metal element M) as the main phase, and more preferably those made of single-phase ε-Fe2O3.

[0052] The firing time is preferably from 10 hours to 200 hours. When the firing time is 10 hours or more, the inside of the γ-iron oxide particles can be effectively transformed into ε-iron oxide. On the other hand, when the firing time is 200 hours or less, the disappearance of γ-iron oxide can be effectively suppressed.

[0053] The firing temperature is preferably 950° C. or higher and 1400° C. or lower. When the firing temperature is 950° C. or higher, the inside of the γ-iron oxide particles can be effectively transformed into ε-iron oxide. On the other hand, when the firing temperature is 1400° C. or lower, the disappearance of γ-iron oxide can be effectively suppressed.

[0054] Before the entire γ-iron oxide particles are transformed into ε-iron oxide, the sintering furnace is cooled to room temperature and the obtained magnetic powder is removed from the sintering furnace, thereby obtaining a magnetic powder containing the magnetic particles 20 shown in FIG.

[0055] [effect] The magnetic powder according to the second embodiment can provide the same effects as the magnetic powder according to the first embodiment. Moreover, the method for producing the magnetic powder according to the second embodiment can provide the same effects as the method for producing the magnetic powder according to the first embodiment.

[0056] <3. Third embodiment> [Configuration of magnetic recording medium] A magnetic recording medium 30 according to a third embodiment of the present disclosure is a so-called tape-shaped magnetic recording medium, and as shown in Fig. 3, includes a long substrate 31, an underlayer (non-magnetic layer) 32 provided on one main surface of the substrate 31, and a recording layer (magnetic layer) 33 provided on the underlayer 32. The underlayer 32 is provided as necessary, but may not be required. The magnetic recording medium may further include a backcoat layer 34 provided on the other main surface of the substrate 31 as necessary.

[0057] (Saturation magnetization M s ) Saturation magnetization amount M of the recording layer 33 s 50 emu / cc≦M s It is preferable that the saturation magnetization M is ≦110 emu / cc. s If the saturation magnetization is 50 emu / cc or less, a higher output can be obtained, and therefore better electromagnetic conversion characteristics (e.g., CNR) can be obtained. On the other hand, the saturation magnetization M s M s If the density is ≦110 emu / cc, the occurrence of saturation of the reproducing head can be suppressed, and the occurrence of noise can be suppressed, thereby further improving the electromagnetic conversion characteristics (e.g., CNR) of the magnetic recording medium.

[0058] The above saturation magnetization M sis obtained as follows. First, three long magnetic recording media 30 are stacked with double-sided tape, and then punched out with a φ6.39 mm punch to prepare a measurement sample. At this time, marking is performed with any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium 10 can be recognized. Then, the MH loop of the entire measurement sample (entire magnetic recording medium 30) corresponding to the vertical direction (thickness direction) of the measurement sample is measured using a VSM. Next, the coating film (undercoat layer 32, recording layer 33, backcoat layer 34, etc.) is wiped off with acetone or ethanol, etc., leaving only the substrate 31. Then, three obtained substrates 31 are stacked with double-sided tape, and then punched out with a φ6.39 mm punch to prepare a sample for background correction (hereinafter simply referred to as a "correction sample"). Then, the MH loop of the correction sample (substrate 31) corresponding to the vertical direction (thickness direction) of the substrate 31 is measured using a VSM.

[0059] The MH loop of the measurement sample (the entire magnetic recording medium 30) and the MH loop of the correction sample (substrate 311) are measured using a high-sensitivity vibration sample magnetometer "VSM-P7-15 type" manufactured by Toei Industry Co., Ltd. The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, number of MH averages: 20.

[0060] After the MH loop of the measurement sample (entire magnetic recording medium 10) and the MH loop of the correction sample (base layer 11) are obtained, background correction is performed by subtracting the MH loop of the correction sample (substrate 31) from the MH loop of the entire measurement sample (entire magnetic recording medium 30) to obtain the MH loop after background correction. A measurement and analysis program attached to the "VSM-P7-15" is used for the calculation of this background correction. The saturation magnetization m s(emu) is calculated. Note that all of the above MH loop measurements are performed at 25° C. Furthermore, it is assumed that no “demagnetization field correction” is performed when measuring the MH loop in the perpendicular direction to the magnetic recording medium 30.

[0061] Next, a carbon layer is formed on the surface of the magnetic recording medium 30 on the recording layer 33 side and on the surface of the back layer 34 side by a vapor deposition method, and then a tungsten layer is further formed on the surface on the recording layer 33 side by a vapor deposition method. These layers are formed to protect the sample in the flaking process described below. Next, the magnetic recording medium 30 on which the above layers are formed is processed by a FIB (Focused Ion Beam) method to perform flaking. The flaking is performed along the length direction (longitudinal direction) of the magnetic recording medium 30. In other words, the flaking forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 30.

[0062] The cross section of the obtained thinned sample is observed by a TEM to obtain a TEM image. The magnification and acceleration voltage may be appropriately adjusted depending on the type of device. The device and observation conditions used for the observation are shown below. Equipment: TEM (Hitachi H9000NAR) Acceleration voltage: 300 kV Magnification: 100,000x Next, using the obtained TEM image, the thickness of the recording layer 33 is measured at at least 10 positions in the longitudinal direction of the magnetic recording medium 30, and then these measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness d of the recording layer 33. Note that the measurement positions are selected at random from the test piece.

[0063] Next, the volume v (=S×d) (cc) of the measurement sample used in the measurement of the MH loop is calculated using the area S of the measurement sample and the average thickness d of the recording layer 33. Then, the calculated volume v (cc) and the saturation magnetization m s (emu) and the saturation magnetization m s Calculate (emu / cc).

[0064] (The coercive force H c ) Coercive force H in the perpendicular direction c The upper limit of the coercive force H is 3000 Oe or less, more preferably 2900 Oe or less, and further preferably 2850 Oe or less. c A large coercive force H c If the magnetic field exceeds 3000 Oe, it becomes difficult for the recording head to perform saturation recording, which may result in some areas that cannot be recorded and an increase in noise, which may result in a deterioration in the electromagnetic conversion characteristics (e.g., CNR).

[0065] Coercive force H in the perpendicular direction c The lower limit of the coercive force H is preferably 2200 Oe or more, more preferably 2400 Oe or more, and even more preferably 2600 Oe or more. c If the magnetic field strength is 2200 Oe or more, it is possible to suppress the deterioration of electromagnetic conversion characteristics (for example, CNR) in a high-temperature environment caused by the influence of thermal disturbance and the influence of a demagnetizing field.

[0066] The above coercive force H c can be calculated as follows. First, the above-mentioned saturation magnetization M s The background-corrected MH loop is then calculated from the obtained MH loop. c Request.

[0067] (Base) The substrate 31 serving as the support is a long, flexible non-magnetic substrate. The non-magnetic substrate is a film, and the thickness of the film is, for example, 3 μm or more and 8 μm or less. The substrate 31 may be made of, for example, polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, plastics such as polycarbonate, polyimide, and polyamideimide, light metals such as aluminum alloys and titanium alloys, and ceramics such as alumina glass.

[0068] (Recording layer) The recording layer 33 contains, for example, the magnetic powder, binder, and conductive particles according to the first embodiment. The recording layer 33 may further contain additives such as a lubricant, an abrasive, and an anti-rust agent, as necessary.

[0069] As the binder, a resin having a structure in which a crosslinking reaction is given to a polyurethane resin, a vinyl chloride resin, or the like is preferable. However, the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required for the magnetic recording medium. The resin to be blended is not particularly limited as long as it is a resin generally used in coating-type magnetic recording media.

[0070] Examples of the polymer include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butadiene copolymer, polyester resin, amino resin, and synthetic rubber.

[0071] Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, and urea formaldehyde resin.

[0072] Furthermore, in order to improve the dispersibility of the magnetic powder, polar functional groups such as -SO3M, -OSO3M, -COOM, and P=O(OM)2 may be introduced into each of the above-mentioned binders, where M is a hydrogen atom or an alkali metal such as lithium, potassium, or sodium.

[0073] Furthermore, the polar functional group is -NR1R2, -NR1R2R3 + X - Side chain type with terminal group of >NR1R2 + X - In the formula, R1, R2, and R3 are hydrogen atoms or hydrocarbon groups, and X - is a halogen element ion such as fluorine, chlorine, bromine, or iodine, or an inorganic or organic ion. Examples of the polar functional group include -OH, -SH, -CN, and an epoxy group.

[0074] The recording layer 33 may further contain non-magnetic reinforcing particles such as aluminum oxide (α, β or γ alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile or anatase type titanium oxide), etc.

[0075] The average thickness of the recording layer 33 is preferably 30 nm or more and 120 nm or less, and more preferably 50 nm or more and 70 nm or less. The method for calculating the average thickness of the recording layer 33 is as described above.

[0076] (base layer) The underlayer 32 is a non-magnetic layer containing non-magnetic powder and a binder as main components. If necessary, the underlayer 32 may further contain at least one additive selected from the group consisting of conductive particles, lubricants, hardeners, and rust inhibitors.

[0077] The non-magnetic powder may be an inorganic or organic substance. The non-magnetic powder may be carbon black or the like. Examples of inorganic substances include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. The shape of the non-magnetic powder may be, for example, various shapes such as needles, spheres, cubes, and plates, but is not limited thereto. The binder is the same as that of the recording layer 33 described above.

[0078] The average thickness of the underlayer 32 is preferably 0.6 μm or more and 2.0 μm or less, and more preferably 0.8 μm or more and 1.4 μm or less. The method for calculating the average thickness of the underlayer 32 is the same as the method for calculating the average thickness of the recording layer 33 described above.

[0079] [Method of manufacturing magnetic recording media] Next, an example of a method for manufacturing a magnetic recording medium having the above-mentioned configuration will be described. First, a paint for forming an undercoat layer is prepared by kneading and dispersing a non-magnetic powder, a binder, etc. in a solvent. Next, a paint for forming a recording layer is prepared by kneading and dispersing a magnetic powder, a binder, etc. according to the first embodiment in a solvent. For example, the following solvents, dispersing devices, and kneading devices can be used to prepare the paint for forming a recording layer and the paint for forming an undercoat layer.

[0080] Examples of the solvent used in preparing the coating material include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, alcohol-based solvents such as methanol, ethanol, and propanol, ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol acetate, ether-based solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane, aromatic hydrocarbon-based solvents such as benzene, toluene, and xylene, and halogenated hydrocarbon-based solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene. These may be used alone or in appropriate mixture.

[0081] Examples of the kneading device used in the preparation of the above-mentioned coating material include, but are not limited to, a continuous twin-screw kneader, a continuous twin-screw kneader capable of diluting in multiple stages, a kneader, a pressure kneader, a roll kneader, etc. Examples of the dispersing device used in the preparation of the above-mentioned coating material include, but are not limited to, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a pearl mill (for example, "DCP Mill" manufactured by Eirich Co., Ltd.), a homogenizer, an ultrasonic dispersing machine, etc.

[0082] Next, a paint for forming an underlayer is applied to one main surface of the substrate 31 and dried to form the underlayer 32. Next, a paint for forming a recording layer is applied to the underlayer 32 and dried to form the recording layer 33 on the underlayer 32. During drying, the magnetic powder may be magnetically oriented in the thickness direction of the substrate 31 by, for example, a solenoid coil. Next, if necessary, a lubricant layer may be formed on the recording layer 33, or a backcoat layer 34 may be formed on the other main surface of the substrate 31.

[0083] Next, the substrate 31 on which the underlayer 32 and the recording layer 33 are formed is rewound around a large diameter core and hardened. Next, the substrate 31 on which the underlayer 32 and the recording layer 33 are formed is calendered and then cut to a predetermined width. In this manner, the desired magnetic recording medium 30 is obtained.

[0084] [effect] In the magnetic recording medium 30 according to the third embodiment of the present disclosure, the recording layer 33 contains the magnetic powder according to the first embodiment, and therefore it is possible to realize a magnetic recording medium 30 that has high output, excellent thermal stability, and ease of recording. EXAMPLES

[0085] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.

[0086] [Examples 1 to 4, 8, 11, 12, and 15] The manufacturing process of the magnetic powder will be described below with reference to Fig. 4. First, in step S11, the ε-Fe2O3 particles were weighed, placed on a quartz boat, and charged into a tubular furnace. In this case, the ε-Fe2O3 particles had an average particle radius almost identical to the average particle radius r (see Table 1) of the magnetic powder finally obtained. After charging, in step S12, the atmosphere in the tubular furnace was replaced with N2 atmosphere once, and in step S13, the temperature of the tubular furnace was raised to a predetermined temperature (350°C).

[0087] After the temperature was raised, in step S14, 240 ml of reducing gas with a H2 concentration of 4% was supplied and heat treatment was performed at 350°C. More specifically, the heat treatment was performed for 24 minutes while supplying reducing gas with a H2 concentration of 4% at 10 ml / min. As a result, the surface of the ε-Fe2O3 particles was reduced and transformed into Fe3O4. Here, the supply amount of reducing gas, 240 ml, means the total amount of reducing gas supplied during reduction. Thereafter, in step S15, the atmosphere was replaced with N2 again, and in step S16, the tubular furnace was cooled to room temperature. As a result, core-shell type magnetic particles having a Fe3O4 layer on the surface were obtained. Finally, in step S17, the obtained magnetic powder was collected.

[0088] [Examples 5 to 7, 13, and 14] In step S14, as shown in Table 1, magnetic powder was obtained in the same manner as in Example 2, except that the total amount of reducing gas with an H2 concentration of 4% was changed to 80 ml (Example 13), 160 ml (Example 5), 320 ml (Example 6), 400 ml (Example 7), and 480 ml (Example 14).

[0089] [Examples 9 and 10] Hereinafter, the manufacturing process of the magnetic powder will be described with reference to Fig. 5. First, in step S21, the FeO particles were weighed, placed on a quartz boat, and put into a sintering furnace. At this time, Fe2O3 particles having an average particle radius almost the same as the average particle radius r (see Table 1) of the finally obtained magnetic powder were prepared as the FeO particles. After the input, in step S22, the sintering furnace was heated to a predetermined temperature (1100°C).

[0090] After the temperature increase, in step S23, a firing treatment was performed at 1100°C for 50 hours (Example 9) and at 1100°C for 70 hours (Example 10), as shown in Table 1. As a result, the FeO particles were transformed into γ-iron oxide particles, and then the inside of the γ-iron oxide particles was transformed into ε-iron oxide. The firing treatment was performed in an air atmosphere. Then, in step S24, the firing furnace was cooled to room temperature before the entire γ-iron oxide particles were transformed into ε-iron oxide. As a result, core-shell type magnetic particles having a γ-iron oxide layer on the surface were obtained. Finally, in step S25, the obtained magnetic powder was collected.

[0091] [Evaluation of magnetic powder] The magnetic powder obtained as described above was evaluated as follows.

[0092] (average particle radius r) The average particle radius r of the magnetic particles was calculated in the same manner as described in the first embodiment above.

[0093] (The average radius of the core r h ) The average radius r of the core portion 11 described in the first embodiment h It was calculated in the same manner as in the calculation method of the ratio R2 (explained in the calculation method of the ratio R2).

[0094] (Ratio R1 of standard deviation σ of particle size distribution to average particle diameter D) It was calculated in the same manner as the calculation method for the ratio R1 of the standard deviation σ of the particle size distribution to the average particle diameter D described in the first embodiment above.

[0095] (average volume of magnetic particles V) It was calculated in the same manner as the calculation method for the average volume V of the magnetic particles explained in the first embodiment above (explained in the calculation method for the ratio R2).

[0096] (Average core volume V h ) The average volume V of the core portion described in the first embodiment h It was calculated in the same manner as in the calculation method of the ratio R2 (explained in the calculation method of the ratio R2).

[0097] (The average volume of the shell V s ) The average volume V of the shell portion described in the first embodiment s It was calculated in the same manner as in the calculation method of the ratio R2 (explained in the calculation method of the ratio R2).

[0098] (Average volume of the shell V relative to the average volume of the magnetic particles V) s Ratio of The average volume V of the shell portion relative to the average volume V of the magnetic particles described in the first embodiment above s The ratio was calculated in the same manner as R2.

[0099] (Saturation magnetization amount σ s ) The saturation magnetization amount σ of the magnetic particles described in the first embodiment s It was calculated in the same manner as above.

[0100] [Magnetic tape evaluation] A magnetic tape was produced using the magnetic powder obtained as described above, and the following evaluations were carried out. The magnetic tape used for the evaluations was produced as follows.

[0101] (Preparation process of paint for forming recording layer) The coating material for forming the recording layer was prepared as follows. First, the first composition having the following composition was mixed with an extruder. Next, the mixed first composition and the second composition having the following composition were added to a stirring tank equipped with a disperser and premixed. Then, further mixing was performed with a sand mill and filtering was performed to prepare the coating material for forming the recording layer.

[0102] (First composition) Magnetic powder: 100 parts by mass Vinyl chloride resin (cyclohexanone solution 30% by mass): 10 parts by mass (Degree of polymerization: 300, Mn=10,000, contains polar groups OSO3K=0.07mmol / g and secondary OH=0.3mmol / g.) Aluminum oxide powder: 5 parts by weight (α-Al2O3, average particle size 0.2μm) Carbon black: 2 parts by weight (Manufactured by Tokai Carbon Co., Ltd., product name: Seast TA) As the magnetic powder, the magnetic powders of Examples 1 to 15 (see Table 1) were used.

[0103] (Second composition) Vinyl chloride resin: 1.1 parts by mass (Resin solution: resin 30% by mass, cyclohexanone 70% by mass) n-Butyl stearate: 2 parts by weight Methyl ethyl ketone: 121.3 parts by mass Toluene: 121.3 parts by mass Cyclohexanone: 60.7 parts by mass

[0104] Finally, 4 parts by mass of polyisocyanate (product name: Coronate L, manufactured by Nippon Polyurethane Industries, Ltd.) and 2 parts by mass of myristic acid were added as a curing agent to the coating material for forming a recording layer prepared as described above.

[0105] (Preparation process of paint for forming base layer) The coating material for forming the undercoat layer was prepared as follows. First, the third composition having the following composition was mixed with an extruder. Next, the mixed third composition and the fourth composition having the following composition were added to a stirring tank equipped with a disperser and premixed. Then, further mixing was performed with a sand mill and filtering was performed to prepare the coating material for forming the undercoat layer.

[0106] (Third composition) Acicular iron oxide powder: 100 parts by weight (α-Fe2O3, average major axis length 0.15μm) Vinyl chloride resin: 55.6 parts by mass (Resin solution: resin 30% by mass, cyclohexanone 70% by mass) Carbon black: 10 parts by weight (Average particle size 20nm)

[0107] (4th composition) Polyurethane resin UR8200 (manufactured by Toyobo): 18.5 parts by weight n-Butyl stearate: 2 parts by weight Methyl ethyl ketone: 108.2 parts by mass Toluene: 108.2 parts by mass Cyclohexanone: 18.5 parts by mass

[0108] Finally, 4 parts by mass of polyisocyanate (product name: Coronate L, manufactured by Nippon Polyurethane Industries, Ltd.) as a curing agent and 2 parts by mass of myristic acid were added to the coating material for forming the undercoat layer prepared as described above.

[0109] (Preparation process of paint for forming back layer) The coating material for forming the back layer was prepared as follows: The following raw materials were mixed in a stirring tank equipped with a disperser, and the mixture was filtered to prepare the coating material for forming the back layer. Carbon black (manufactured by Asahi Corporation, product name: #80): 100 parts by weight Polyester polyurethane: 100 parts by weight (Manufactured by Nippon Polyurethane Co., Ltd., product name: N-2304) Methyl ethyl ketone: 500 parts by weight Toluene: 400 parts by mass Cyclohexanone: 100 parts by mass

[0110] (Film forming process) Using the coating material prepared as described above, a magnetic tape was prepared as follows. First, a long PEN film (base film) having 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 main surface of the PEN film and dried to form an undercoat layer having an average thickness of 1.1 μm on the PEN film. Next, a coating material for forming a recording layer was applied to the undercoat layer and dried to form a recording layer having an average thickness of 0.1 μm on the undercoat layer. During drying of the coating material for forming a recording layer, the magnetic powder was magnetically oriented in the thickness direction of the PEN film by a solenoid coil.

[0111] Next, the paint for forming the back layer was applied to the other main surface of the PEN film and dried to form a back layer with an average thickness of 0.4 μm. Then, the PEN film on which the undercoat layer, recording layer, and back layer were formed was subjected to a curing treatment. After that, a calendar treatment was performed to smooth the surface of the recording layer.

[0112] (Cutting process) The magnetic tape obtained as described above was cut into a width of 1 / 2 inch (12.65 mm), thereby obtaining a long magnetic tape with an average thickness of 5.6 μm.

[0113] (Magnetic tape saturation magnetization Ms) The amount of saturation magnetization Ms of the magnetic tape was calculated in the same manner as described in the third embodiment above.

[0114] (Magnetic tape coercivity H c ) The coercive force H of the magnetic tape described in the third embodiment c It was calculated in the same manner as above.

[0115] (CNR) First, a loop tester (Microphysics) was used to obtain a playback signal from the magnetic tape. The conditions for obtaining the playback signal are as follows: head:GMR head speed:2m / s signal: single recording frequency (10MHz) Recording current: Optimum recording current

[0116] Next, the reproduction signal was captured by a spectrum analyzer, and the reproduction output value of 10 MHz and the average value of the noise of 10 MHz ± 1 MHz were measured, and the difference between them was taken as the CNR. The results are shown in Table 1 as relative values ​​with the CNR of Example 15 taken as 0 dB.

[0117] Table 1 shows the evaluation results of the magnetic powders of Examples 1-15, and the evaluation results of the magnetic tapes produced using the magnetic powders of Examples 1-15. [Table 1]

[0118] The above evaluation results revealed the following: Magnetic particles having a core-shell structure can be obtained by subjecting the surfaces of ε-iron oxide particles to a reduction treatment using a gas-phase reduction method. Magnetic particles having a core-shell structure can be obtained by sintering FeO particles to transform them into γ-iron oxide particles, and then transforming the inside of the γ-iron oxide particles into ε-iron oxide.

[0119] From the viewpoint of improving the CNR, it is preferable that the average particle radius r of the magnetic particles is 4 nm≦r≦20 nm. From the viewpoint of improving the CNR, it is preferable that the ratio R1 (=(σ / D)×100) of the standard deviation σ of the particle size distribution of the magnetic particles to the average particle size D of the magnetic particles is R1≦40%. From the viewpoint of improving the CNR, the average volume of the shell part V s But 90 nm 3 ≦V sand the average volume V of the shell with respect to the average volume V of the magnetic particles s The proportion of R2(=(V s / V)×100) is preferably within the range of 16%≦R2≦62%. From the viewpoint of improving the CNR, the saturation magnetization of the magnetic particles σ s However, 30 emu / g≦σ s It is preferred that it is ≦60 emu / g. From the viewpoint of improving the CNR, the saturation magnetization M s However, 50 emu / cc≦M s It is preferred that it is ≦110 emu / cc. From the viewpoint of improving the CNR, the magnetic particles have the above-mentioned average particle radius r, the ratio R1, the ratio R2, and the saturation magnetization amount σ s It is particularly preferable that all of the above numerical ranges are satisfied.

[0120] [Variations] Although the first to third embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described first to third embodiments, and various modifications based on the technical concept of the present disclosure are possible.

[0121] For example, the configurations, methods, steps, shapes, materials, and values ​​given in the first to third embodiments are merely examples, and different configurations, methods, steps, shapes, materials, and values ​​may be used as necessary. Also, the chemical formulas of compounds, etc. are representative, and are not limited to the valences, etc. given as long as they are general names of the same compounds.

[0122] Furthermore, the configurations, methods, steps, shapes, materials, numerical values, and the like of the first to third embodiments described above can be combined with one another without departing from the spirit of the present disclosure.

[0123] In addition, in the method for producing a magnetic powder according to the first embodiment described above, the powder of ε-iron oxide particles is reduced by a gas phase reduction method. However, the powder of ε-iron oxide particles may be reduced by a liquid phase reduction method.

[0124] In addition, in the manufacturing method of magnetic powder according to the second embodiment described above, the case where the interior of the γ-iron oxide particles is transformed into ε-iron oxide has been described, but by adjusting the sintering conditions, it is also possible to transform a portion of the γ-iron oxide particles other than the interior into ε-iron oxide.

[0125] In addition, in the manufacturing method of the third embodiment described above, the case where the recording layer 33 contains the magnetic powder according to the first embodiment has been described, but the recording layer 33 may contain the magnetic powder according to the second embodiment, or may contain both the magnetic powder according to the first embodiment and the magnetic powder according to the second embodiment.

[0126] The present disclosure may also employ the following configuration. (1) The magnetic particles are obtained by subjecting particles containing ε-iron oxide (including those in which a portion of the Fe site is substituted with a metal element) to a reduction treatment to form triiron tetroxide (including those in which a portion of the Fe site is substituted with the metal element) on at least a portion of the surface of the particles. A method for producing a magnetic powder comprising the steps of: (2) The method for producing a magnetic powder according to (1), wherein the average particle radius r of the magnetic particles is 4 nm≦r≦20 nm. (3) The method for producing a magnetic powder according to (1) or (2), wherein the ratio R1 (=(σ / D)×100) of the standard deviation σ of the particle size distribution of the magnetic particles to the average particle diameter D of the magnetic particles is R1≦40%. (4) The method for producing a magnetic powder according to any one of (1) to (3), wherein the magnetic particles have a core-shell structure. (5) The average volume V of the shell of the magnetic particle s But 90 nm 3 ≦V s and The average volume V of the shell portion with respect to the average volume V of the magnetic particles s The proportion of R2(=(V s / V)×100) is 16%≦R2≦62%. (6) The saturation magnetization amount σ of the magnetic particles s However, 30 emu / g≦σ s A method for producing a magnetic powder according to any one of (1) to (5), wherein the magnetic powder has a molecular weight of ≦60 emu / g. (7) Particles containing ε-iron oxide (including those in which a portion of the Fe site is replaced with a metal element); triiron tetroxide (including those in which a part of the Fe site is substituted with the metal element) provided on at least a part of the surface of the particle; A magnetic powder comprising magnetic particles comprising: (8) (7) A magnetic recording medium comprising a recording layer containing the magnetic powder according to (7). (9) The saturation magnetization amount M of the recording layer s However, 50 emu / cc≦M s ≦110 emu / cc. (10) By calcining, first particles containing ferrous oxide (including those in which a part of the Fe site is substituted with a metal element) are transformed into second particles containing γ-iron oxide (including those in which a part of the Fe site is substituted with the metal element), and then a part of the second particles is transformed into ε-iron oxide (including those in which a part of the Fe site is substituted with the metal element), thereby obtaining magnetic particles. A method for producing a magnetic powder comprising the steps of: (11) The method for producing a magnetic powder according to (10), wherein a part of the second particle is inside the second particle. (12) The method for producing a magnetic powder according to (11), wherein the magnetic particles have a core-shell structure. (13) Particles containing ε-iron oxide (including those in which a portion of the Fe site is replaced with a metal element); γ-iron oxide (including those in which a part of the Fe site is substituted with the metal element) provided on at least a part of the surface of the particle; A magnetic powder comprising magnetic particles comprising: (14) A magnetic recording medium comprising a recording layer containing the magnetic powder according to (13). [Explanation of symbols]

[0127] 10, 20 magnetic particles 11, 21 Core section 12, 22 Shell part 30 Magnetic Recording Media 31 Base 32 Base layer 33 Recording layer 34 Backcoat Layer

Claims

1. A recording layer containing magnetic powder is provided, the magnetic powder includes magnetic particles having a particle containing ε-iron oxide and iron oxide provided on at least a portion of the surface of the particle, The iron oxide includes iron trioxide or gamma-iron oxide, The ratio R of the standard deviation σ of the particle size distribution of the magnetic particles to the average particle diameter D of the magnetic particles １ (=(σ / D)×100) is R １ ≦40%; Magnetic recording media.

2. A recording layer containing magnetic powder is provided, the magnetic powder includes magnetic particles having a particle containing ε-iron oxide and iron oxide provided on at least a portion of the surface of the particle, The ratio R of the standard deviation σ of the particle size distribution of the magnetic particles to the average particle diameter D of the magnetic particles １ (=(σ / D)×100) is R １ ≦40%, The saturation magnetization Ms of the magnetic recording medium in the perpendicular direction is 50 emu / cc≦Ms≦110 emu / cc. Magnetic recording media.

3. A recording layer containing magnetic powder is provided, the magnetic powder includes magnetic particles having a particle containing ε-iron oxide and iron oxide provided on at least a portion of the surface of the particle, The ratio R of the standard deviation σ of the particle size distribution of the magnetic particles to the average particle diameter D of the magnetic particles １ (=(σ / D)×100) is R １ ≦40%, The magnetic recording medium has a coercive force Hc in the perpendicular direction of 3000 Oe or less. Magnetic recording media.

4. The iron oxide includes a soft magnetic material.

4. The magnetic recording medium according to claim 2 or 3.

5. The ε-iron oxide includes those in which a part of the Fe site is replaced with a metal element.

5. The magnetic recording medium according to claim 2.

6. The iron oxide includes one in which a part of the Fe site is substituted with the metal element.

6. The magnetic recording medium according to claim 5.

7. The metal element includes a trivalent metal element.

7. The magnetic recording medium according to claim 5 or 6.

8. The metal element includes at least one of Al, Ga, and In.

7. The magnetic recording medium according to claim 5 or 6.

9. The magnetic particles have a core-shell structure. The magnetic recording medium according to claim 1 .

10. The average volume V of the shell of the magnetic particle ｓ But 90 nm ３ ≦V ｓ That is, 10. The magnetic recording medium according to claim 9.

11. The average volume V of the shell of the magnetic particle relative to the average volume V of the magnetic particle ｓ The ratio R ２ (=(V ｓ / V) × 100) is 16%≦R ２ ≦62%; 11. The magnetic recording medium according to claim 9 or 10.

12. The average particle radius r of the magnetic particles is 4 nm≦r≦20 nm. The magnetic recording medium according to claim 1 .

13. Further comprising a substrate comprising a polyester-based resin; The magnetic recording medium according to claim 1 .

14. Further comprising a substrate; The average thickness of the substrate is 4.0 μm or less. The magnetic recording medium according to claim 1 .

15. The average thickness of the recording layer is 30 nm or more and 120 nm or less. The magnetic recording medium according to claim 1 .

16. The average thickness of the recording layer is 50 nm or more and 70 nm or less. The magnetic recording medium according to claim 15.

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