JP3889635B2 - Perpendicular magnetic recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium used in a magnetic disk or the like, and more particularly to a two-layer perpendicular magnetic recording medium in which a perpendicular magnetization film is formed as a magnetic recording layer on a soft magnetic underlayer.
[0002]
[Prior art]
While there is a demand for an increase in capacity of hard disk drives, research and development of perpendicular magnetic recording, which is positioned as the next-generation high-density magnetic recording technology, is being actively conducted. Magnetic recording media used for perpendicular magnetic recording are roughly divided into a single-layer perpendicular magnetic recording medium whose magnetic layer is only a magnetic recording layer (perpendicular magnetization film) and a soft magnetic underlayer that assists writing in addition to the magnetic recording layer. There are two types of two-layer perpendicular magnetic recording media.
[0003]
For writing data to this perpendicular magnetic recording medium, a single-pole head is generally used. However, in the case of a two-layer perpendicular magnetic recording medium, the perpendicular head magnetic field at the time of writing becomes large and ideal perpendicular recording becomes possible. Become. For this reason, the two-layer perpendicular magnetic recording medium is attracting attention as a high-density magnetic recording medium.
[0004]
For example, as shown in FIG. 9, a two-layer perpendicular magnetic recording medium having a soft magnetic underlayer includes a soft magnetic underlayer 2, a nonmagnetic layer 3, and a perpendicular magnetization film 4 formed in this order on a substrate 1. The film structure is as follows.
[0005]
[Problems to be solved by the invention]
In order to increase the recording density, it is necessary to form a bit pattern with a fine and clear transition region on the perpendicular magnetic film 4. For this reason, it is necessary that a steep head magnetic field acts on the perpendicular magnetic film 4. Become. However, in the conventional structure, since the soft magnetic underlayer 2 having a high magnetic permeability and a high saturation magnetic flux density exists on the entire back surface of the perpendicular magnetization film 4, the local magnetic flux generated from the recording head is under the soft magnetism. There is a problem that the magnetic field spreads toward the formation 2 and a steep head magnetic field does not act on the perpendicular magnetization film 4 to cope with narrowing of the track.
[0006]
The present invention has been made to solve this problem, and a problem to be solved is to realize a two-layer perpendicular magnetic recording medium in which a steep head magnetic field acts on a perpendicular magnetization film.
[0007]
[Means for Solving the Problems]
The inventor of the present invention pays attention to the fact that in the film structure shown in FIG. 9, the spread of the magnetic field acting on the soft magnetic underlayer can be reduced if the direction of the magnetic flux toward the soft magnetic underlayer can be controlled. The inventors have conceived of providing a film having such a function on the surface of the soft magnetic underlayer, and have completed the present invention.
[0008]
That is, the present invention for solving the above problem is a two-layer perpendicular magnetic recording medium in which a perpendicular magnetization film is formed on a soft magnetic underlayer, and between the soft magnetic underlayer and the perpendicular magnetization film, The magnetic particle has a film magnetically isolated in the in-plane direction.
[0009]
In the present invention, due to the presence of a film in which magnetic particles are magnetically isolated in the in-plane direction, a large amount of magnetic flux emitted from the recording head passes through the isolated magnetic particle portion (high permeability portion) and softens. Since the magnetic head is directed to the magnetic underlayer, the magnetic flux is concentrated on the magnetic particle portion closest to the recording head, the magnetic flux generated from the recording head does not spread toward the soft magnetic underlayer, and a steep head magnetic field is generated in the perpendicular magnetization film. It will work, and it can cope with narrow track.
[0010]
The film provided between the soft magnetic underlayer and the perpendicular magnetization film can be composed of semi-hard ferrite, soft magnetic granular film, or soft magnetic nanocrystal.
As the semi-hard ferrite, γ-Fe ₂ O ₃ , Fe ₃ O ₄ or the like having a needle-like structure is particularly suitable. As the soft magnetic granular film, at least one of the soft magnetic particles selected from Co, Fe, and Ni is used. Preferably, the nonmagnetic base material is made of at least one material selected from SiO ₂ , Al ₂ O ₃ , C, and ZrO ₂ . Further, the soft magnetic nanocrystal is preferably made of a material containing α-Fe particles in an amorphous base.
[0011]
A nonmagnetic layer is preferably provided between the above-mentioned film provided between the soft magnetic underlayer and the perpendicular magnetization film and the perpendicular magnetization film in order to break the magnetic coupling between them.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross-sectional view of an essential part showing an embodiment of the present invention. This embodiment has a film structure in which a soft magnetic underlayer 12, a microcrystalline thin film 13, a nonmagnetic layer 14, a perpendicular magnetization film 15, and a protective film 16 are formed on a substrate 11 in this order.
[0013]
As the substrate 11, a glass substrate is usually used, but another material such as an Al alloy may be used. The soft magnetic underlayer 12 is made of a material selected from FeTaC, FeC, CoZrNb, NiFe, FeAlO, FeN, FeSiAl, and the like. The film thickness is, for example, about 200 nm.
[0014]
An antiferromagnetic layer may be formed adjacent to the soft magnetic underlayer 12 on the substrate 11 side. The antiferromagnetic layer in this case fixes the domain wall of the soft magnetic underlayer 12 and reduces noise such as spike noise peculiar to the two-layer perpendicular magnetic recording medium. For example, IrMn having a film thickness of about 5 nm or the like. It is comprised with the thin film which consists of material. The antiferromagnetic layer and the soft magnetic underlayer 12 may have a multilayer structure including two or more alternating layers.
[0015]
The microcrystalline thin film 13 as a film in which magnetic particles are magnetically isolated in the in-plane direction is composed of a material selected from semi-hard ferrite, soft magnetic granular film, soft magnetic nanocrystal, and the like. When semi-hard ferrite is used as the material of the microcrystalline thin film 13, γ-Fe ₂ O ₃ , Fe ₃ O ₄ or the like having a needle-like structure is particularly suitable.
[0016]
When a soft magnetic granular film is used as the microcrystalline thin film 13, the soft magnetic particles are made of at least one material selected from Co, Fe, and Ni, and the nonmagnetic base material is SiO ₂ , Al ₂ O ₃ , A material made of at least one material selected from C and ZrO ₂ is preferred. Further, when soft magnetic nanocrystals are used as the material of the microcrystalline thin film 13, those made of a material containing α-Fe particles in an amorphous base are preferable.
[0017]
Since the soft magnetic characteristics deteriorate when the soft magnetic underlayer 12 itself is magnetically isolated, in the present invention, a newly magnetically isolated microcrystalline thin film 13 is provided on the soft magnetic underlayer 12. Since the microcrystalline thin film 13 is provided, the spacing between the head and the soft magnetic underlayer 12 may increase, and the soft magnetic characteristics may be deteriorated. A thin film is used as the thin film 13). That is, since the microcrystalline thin film 13 is located between the recording head and the soft magnetic underlayer 12, if the distance between the two is large, the head magnetic field decreases, so that the film thickness is 20 nm or less (most preferably 10 nm or less). )I have to. Further, the particle diameter of the soft magnetic particles of the microcrystalline thin film 13 is, for example, approximately the same as that of the perpendicular magnetization film 15 and is selected to be 20 nm or less.
[0018]
The microcrystalline thin film 13 has a role of assisting the concentration of magnetic flux on the conventional soft magnetic underlayer 12. For this reason, the microcrystalline thin film 13 is magnetically coupled in the film thickness direction and magnetically isolated in the in-plane direction. If the shape of the soft magnetic particles is acicular, it is not impossible to form this film as a thick film.
[0019]
The nonmagnetic layer (intermediate layer) 14 controls the magnetic interaction between the microcrystalline thin film 13 and the perpendicular magnetization film 15 or controls the crystal growth of the perpendicular magnetization film 15 to reduce the noise of the reproduction output. Is. Examples of the material of the nonmagnetic layer 14 include a thin film of Ti, CoZrNb or the like having a film thickness of, for example, 10 nm or less.
[0020]
The perpendicular magnetization film 15 is typically formed of an artificial lattice film, and is formed of a multilayer film such as [Co / Pt], [Co / Pd], [CoCrTa / Pd]. In this case, vertical anisotropy can be easily obtained by controlling the film thickness of Co. As an artificial lattice film, for example, an ultrathin magnetic film of 0.05 nm to 2 nm and an ultrathin nonmagnetic film of 0.05 nm to 5 nm are alternately laminated by a sputtering method or the like, so that the total film thickness is 200 nm or less. The formed one is used.
[0021]
The perpendicular magnetization film 15 may be made of a CoCr alloy or the like instead of an artificial lattice film. For example, a perpendicular magnetic film including CoCrPt, CoCr, CoCrTa, CoCrTaPt, CoCrNbPt, Co / Pd, TbFeCo, and FePt may be used. The perpendicular magnetization film 15 may be formed by selecting a material from an alloy having a directivity. The protective film 16 is made of carbon (C) and has a thickness of about 10 nm. These films are mainly formed using a sputtering method.
[0022]
FIG. 2 is a diagram showing the flow of magnetic flux from the recording head to the magnetic recording medium shown in FIG. 1 (the same parts as those in FIG. 1 are denoted by the same reference numerals). The recording head 20 is a single magnetic pole head (SPT head), and includes a light pole 22 having a rectangular cross section, a rectangular return pole 23 having a larger cross section than the light pole 22, and a driving coil 24. It is configured.
[0023]
As described above, the microcrystalline thin film 13 is magnetically coupled in the film thickness direction and magnetically isolated in the in-plane direction. Therefore, as shown in FIG. 2, the magnetic particles forming the high magnetic permeability portion 13a are arranged in the low magnetic permeability portion 13b so as to be aligned in the film thickness direction and spaced apart in the in-plane direction. Yes. Therefore, a large amount of magnetic flux emitted from the write pole 22 of the recording head 20 travels to the soft magnetic underlayer 12 through the isolated magnetic particle portion (high permeability portion 13a) as shown in FIG. Therefore, the magnetic flux is concentrated on the magnetic particle portion closest to the recording head 20. For this reason, the magnetic flux generated from the write pole 22 of the recording head 20 does not spread toward the soft magnetic underlayer 12, but a steep head magnetic field acts on the perpendicular magnetization film 15, which corresponds to narrowing of the track. it can.
[0024]
When the microcrystalline thin film 13 made of γ-Fe ₂ O _3, which is a semi-hard ferrite having an acicular structure, is used, for example, an FeTaC film of about 200 nm is formed as a soft magnetic underlayer 12 on a glass substrate 11. Then, a γ-Fe ₂ O ₃ film having a thickness of about 10 nm is formed thereon as a microcrystalline thin film 13, a Ti film (nonmagnetic layer 14) having a thickness of about 5 nm, a CoCrPt film (perpendicular magnetization film 15) having a thickness of about 200 nm, and C A film (protective film 16) is formed. The film formation is performed by a sputtering method or the like.
[0025]
Here, γ-Fe ₂ O ₃ which is a semi-hard ferrite is used as a granular film. In the γ-Fe ₂ O ₃ granular film, α-FeOOH is oxidized and reduced by heat treatment to obtain γ-Fe ₂ O ₃ as a final product, which is then mixed with the nonmagnetic base material SiO ₂ . perpendicular anisotropy imparting of γ-Fe ₂ O ₃ after formation of the γ-Fe ₂ O ₃ granular film, performed by heat treatment in a magnetic field.
[0026]
The magnetic properties of γ-Fe ₂ O ₃ and Fe ₃ O ₄ which are semi-hard ferrites having a needle-like structure used for the microcrystalline thin film 13 are as shown in FIG. From FIG. 3, γ-Fe ₂ O ₃ and Fe ₃ O ₄ have a coercive force Hc of about 200 to 450 (unit Oe) and a coercive force sufficiently smaller than that of the perpendicular magnetization film 15. Therefore, it is considered that the particles are isolated to some extent. Further, the particle size is 0.01 to 0.05 μm, which is sufficiently smaller than the magnetization transition width, which is advantageous for narrowing the track.
[0027]
When the microcrystalline thin film 13 is formed with soft magnetic nanocrystals, a material containing α-Fe particles in an amorphous base is used as the soft magnetic nanocrystals. Examples of the material include Fe-MB (M; Zr, Hf, Nb) and Fe-MO (M; Zr, Hf, Nb, Y, Ce). In these materials, α-Fe particles in an amorphous matrix are dispersed with a particle size of about 10 nm to 100 nm, and the crystal particle size (coercive force is reduced depending on the additive element (here, equivalent to M) and heat treatment conditions. And the magnetic permeability (depending on the saturation magnetic flux density Bs) can be changed. The degree of magnetic isolation of the soft magnetic nanocrystal film can be known by measuring the coercive force. This is because, as shown in FIG. 4, the relationship that the magnetic coercive force (Hc / Hk) increases becomes magnetically isolated.
[0028]
In the case of forming the microcrystalline thin film 13 with the FeHfO film, for example, an FeTaC film of about 200 nm is formed as the soft magnetic underlayer 12 on the glass substrate 11, and the FeHfO film of about 10 nm is formed thereon. Then, a Ti film (nonmagnetic layer 14) of about 5 nm, a CoCrPt film (perpendicular magnetization film 15) of about 200 nm, and a C film (protective film 16) of about 10 nm are formed. The film formation is performed by a sputtering method or the like. Giving perpendicular anisotropy to FeHfO is performed by heat treatment in a magnetic field. When Co is added to FeHfO, anisotropy can be strengthened and anisotropic dispersion can be reduced.
[0029]
The difference in the magnetic field distribution on the magnetic recording medium between the conventional structure and the structure of the present invention was obtained and compared by micromagnetic simulation.
In the simulation model, since the recording single pole head interacts with the soft magnetic underlayer, only the single pole head excluding the medium and the soft magnetic underlayer are incorporated. As the structure of the present invention, a magnetically isolated microcrystalline thin film added on a conventional soft magnetic underlayer was used. A top view of the single pole head and the soft magnetic underlayer is shown in FIG. The single-pole head and the soft magnetic underlayer are composed of 20 × 20 × 20 nm ³ grain size units. Next, material parameters of each material are shown.
・ Single pole head (light pole and return pole)
Saturation magnetic flux density Bs = 1 T
Anisotropic magnetic field Hkx = 10 Oe
Distance from the head air bearing surface to the surface of the soft magnetic underlayer (or the soft magnetic thin film added in the present invention) (magnetic spacing + medium film thickness, etc.) 40 nm
Gap length 800nm
Exchange interaction constant A = 1.0 merg / cm (equivalent to Ni80Fe20)
・ Soft magnetic underlayer saturation magnetic flux density Bs = 1 T
Anisotropic magnetic field Hkx = 20 Oe
Exchange interaction constant A = 1.0 merg / cm
Film thickness 100nm
-Soft magnetic thin film (microcrystalline thin film) added in the present invention
Saturation magnetic flux density Bs = 0.57 T
Anisotropy magnetic field Hky = 100 Oe (vertical anisotropy due to needle-like shape anisotropy)
Exchange interaction constant A = 0.0 merg / cm
Film thickness 20nm
As a result of the simulation, FIG. 6 shows the head magnetic field at the center of the track (head magnetic field along the horizontal center line C in FIG. 5) of each medium structure. However, this head magnetic field is a value at a position of 10 nm above the soft magnetic underlayer (in the case of the conventional structure) or the isolated soft magnetic thin film (in the case of the structure of the present invention). In the medium structure of the present invention, the head magnetic field is increased by 150 Oe (about 5% of the maximum magnetic field) despite the 20 nm spacing loss up to the soft magnetic underlayer. FIG. 7 shows the head magnetic field at the off-track position (position shifted in the vertical direction in FIG. 5) at the maximum magnetic field position (point (a) in FIG. 6). In the vicinity of the track edge, according to the medium structure of the present invention, the magnetic field gradient was steep by about 10%, and the result was excellent in narrowing the track.
[0030]
A magnetic disk device incorporating the above embodiment will be described with reference to FIG. FIG. 8 shows the internal structure with the disk enclosure cover removed. In FIG. 8, one or more disks (recording media) 32 that are rotationally driven by a spindle motor (not shown) are arranged in the center of an enclosure 31 that seals the inside of the apparatus, and the vicinity of the outer periphery of the disk 32 In addition, a carriage arm 33 is provided to be rotatable about a shaft 34. The tip of the carriage arm 33 extends in the direction of the disk 32, and a suspension 35 is provided there. A magnetic head (flying head slider) comprising a recording head and a reading head is provided near the tip of the suspension 35. 37 is attached.
[0031]
An actuator (voice coil motor) 36 that rotationally drives the carriage arm 33 is provided on the base end side of the carriage arm 33. The actuator 36 has been widely used conventionally. For example, a magnetic circuit having a magnetic gap is fixed on the enclosure 31 side, and a voice coil (moving coil) is fixed to the carriage arm 33. When a drive current is passed through the voice coil in the actuator 36, a thrust is generated in the voice coil portion in the magnetic gap, the carriage arm 33 rotates, and the magnetic head 37 moves in the track width direction T of the disk 32. It is positioned on a predetermined track, and information is recorded and reproduced.
[0032]
The disk 32 of this magnetic disk apparatus uses the perpendicular magnetic recording medium of the present invention, which makes it possible to narrow the track and cope with an increase in capacity.
In addition, it cannot be overemphasized that this invention is not limited to the material and numerical value which were illustrated by the said example of a form, A various deformation | transformation is possible.
[0033]
【The invention's effect】
As described above, in the present invention, due to the presence of the film in which the magnetic particles are magnetically isolated in the in-plane direction, many magnetic fluxes emitted from the recording head are separated from the isolated magnetic particle portion (high magnetic permeability). To the soft magnetic underlayer. Therefore, according to the present invention, the magnetic flux concentrates on the magnetic particle portion closest to the recording head, and the magnetic flux generated from the recording head does not spread toward the soft magnetic underlayer, and the head is steep in the perpendicular magnetization film. A magnetic field acts, and a perpendicular magnetic recording medium that can cope with a narrow track can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an essential part showing an embodiment of the present invention.
FIG. 2 is a diagram showing the flow of magnetic flux from the recording head to the magnetic recording medium shown in FIG.
FIG. 3 is a diagram showing magnetic characteristics of a semi-hard ferrite having a needle-like structure.
FIG. 4 is a diagram showing the relationship between the degree of magnetic isolation and the coercive force (Hc / Hk).
FIG. 5 is a top view of a model used for simulation.
FIG. 6 is a diagram showing a head magnetic field at the center of a track.
FIG. 7 is a diagram showing a head magnetic field at an off-track position at a maximum magnetic field position (FIG. 6A).
FIG. 8 is a diagram showing an example of a magnetic disk device using the perpendicular magnetic recording medium of the present invention.
FIG. 9 is a cross-sectional view of a main part showing a conventional magnetic recording medium.
[Explanation of symbols]
11 Substrate 12 Soft magnetic underlayer 13 Microcrystalline thin film 13a High magnetic permeability portion 14 Nonmagnetic layer 15 Perpendicular magnetization film 16 Protective film 20 Recording head 22 Write pole 23 Return pole 24 Coil 31 Enclosure 32 Disk 33 Carriage arm 35 Suspension 37 Magnetic head

Claims (2)

2-layered perpendicular magnetic recording medium der the perpendicular magnetization film is formed on the soft magnetic underlayer is, magnetically isolated between the perpendicular magnetization film and the soft magnetic underlayer, the magnetic particles in the plane direction In a perpendicular magnetic recording medium having a structured film ,
The film provided between the soft magnetic underlayer and the perpendicular magnetization film is a granular film, and this granular film is made of semi-hard ferrite. As this ferrite, γ − Fe ₂ O ₃ having a needle-like structure , Fe ₃ O ₄ A perpendicular magnetic recording medium , wherein one of the above is selected . A two-layer perpendicular magnetic recording medium in which a perpendicular magnetic film is formed on a soft magnetic underlayer. Magnetic particles are magnetically isolated in the in-plane direction between the soft magnetic underlayer and the perpendicular magnetic film. In a perpendicular magnetic recording medium having the above film,
The film provided between the soft magnetic underlayer and the perpendicular magnetization film is made of soft magnetic nanocrystals, and the soft magnetic nanocrystals are made of a material containing α - Fe particles in an amorphous base. Perpendicular magnetic recording medium.

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