JP2008052877A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-density magnetic recoding medium in which an increase in demagnetizing field is suppressed in a magnetic recording layer. <P>SOLUTION: In the magnetic recording medium having the magnetic recording layer 5 in which a plurality of magnetic regions 22 are separately provided in a base material made of a nonmagnetic material 21, the magnetic region 22 has at least one soft magnetic layer 23 and at least one hard magnetic layer 25 at least in an in-plane direction of the magnetic recording layer, and a nonmagnetic layer 24 made of a nonmagnetic material between the soft magnetic layer 23 and the hard magnetic layer 25. The average magnetic anisotropy energy density of the soft magnetic layer is preferably smaller than the average magnetic anisotropy energy density of the hard magnetic layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium capable of high density magnetic recording.

  In recent years, as the amount of information increases, it is expected that the surface recording density of a magnetic recording medium such as a hard disk drive (hereinafter referred to as “HDD”) is improved, and the recording bit size on the magnetic recording medium is about several tens of nm. It has become extremely fine.

  In the conventional longitudinal magnetic recording type magnetic recording medium, since the demagnetizing field in the recording bit in the high recording density region becomes strong, it is easily affected by “thermal fluctuation” from a relatively large magnetic particle diameter. On the other hand, in the magnetic recording medium of the perpendicular magnetic recording system, by growing the magnetic particles in the film thickness direction, the minimum unit volume of magnetization can be increased while the particle diameter of the medium surface is small. Since it can be suppressed, it is expected as a further high-density recording method.

  Conventionally, alloy materials such as CoCrPt and CoCrTa have been mainly used as magnetic recording layer materials for perpendicular magnetic recording media employing the perpendicular magnetic recording system. In these alloy materials, Cr, which is a nonmagnetic material, segregates at the crystal grain boundaries, so that individual crystal grains are magnetically separated, and the characteristics necessary for a magnetic recording medium such as high coercive force (Hc) are exhibited. . Such segregation of Cr to the crystal grain boundary has been promoted in the in-plane medium by devising a film forming process such as heating or applying a substrate bias.

  However, the perpendicular magnetic recording medium has a problem in that the amount of Cr segregation is small even when heating or substrate bias application is performed as in the case of the in-plane medium, and the medium noise increases due to this.

As a method for solving this problem, there has been proposed a granular medium that promotes magnetic separation of crystal grains by segregating oxides and nitrides to crystal grain boundaries. For example, in a CoCrPt—SiO ₂ granular film, the CoCrPt crystal grains are segregated so as to surround the SiO ₂ , whereby the individual CoCrPt crystal grains are magnetically separated. As described above, the granular film is characterized in that it does not use phase separation (magnetic phase separation) of the alloy material but adds an amorphous material that is not easily dissolved in the alloy material, such as oxide or nitride. Therefore, it has been confirmed that medium noise can be reduced as compared with a medium using a conventional CoCr-based material as a magnetic recording layer.

  Further, a medium configuration as disclosed in Patent Document 1 is disclosed for the purpose of breaking the magnetic coupling. In Patent Document 1, a magnetic material is combined with nanometer-sized holes (hereinafter referred to as nanoholes) formed in a self-organized manner in a non-magnetic material layer, thereby coupling the magnetic materials combined in each hole. Is effectively divided as compared with a granular medium, so that the effect of reducing medium noise is great.

  As a method for creating nanoholes in such a self-organized manner, for example, in Patent Document 1, a material in which a phase-separated structure is formed is used to form a structure in which columnar members are dispersed in a region surrounding the columnar member. A method for obtaining a porous layer by removing these members is disclosed.

Patent Document 2 discloses a method of forming holes by anodizing aluminum or an alloy containing aluminum in a solution such as oxalic acid or phosphoric acid.
Examples of nonmagnetic layers forming nanoholes include oxides such as SiO ₂ , Al ₂ O ₃ , and TiO ₂ , nitrides such as Si ₃ N ₄ , AlN, and TiN, carbides such as TiC, and borides such as BN. And a ferromagnetic region is selectively formed in these nonmagnetic layers.

  In particular, in perpendicular recording media in which magnetic materials are combined with nanoholes such as these, isolated magnetic regions can be periodically arranged to record one bit in one isolated magnetic region, thereby achieving higher density recording. Is expected to be.

  However, in order to achieve high density recording by recording 1 bit in such an isolated magnetic region, if the surface density of the isolated region is increased, the recording magnetization tends to become unstable due to the demagnetizing field. Was.

  In particular, in the case of perpendicular magnetic recording, a magnetic pole is generated on the surface of the magnetic recording layer, and as the density of the isolated magnetic region is increased, the density of the magnetic pole generated on the surface of the magnetic recording layer is increased. This effect appears as deterioration of the medium squareness ratio when the perpendicular magnetic recording medium is evaluated by a normal MH loop. That is, the slope of the increase in magnetization with respect to the holding force Hc of the MH loop curve versus the increase in applied magnetic field ΔM / ΔH is small, and when the magnitude of the coercive force is small, the magnitude of the residual magnetization when there is no applied magnetization. Make it smaller. In addition, the occurrence of noise during recording increases due to the influence of the demagnetizing field.

  In order to prevent the influence of such a demagnetizing field, in Patent Document 3, a plurality of isolated magnetic regions separated by non-recording regions are patterned, and a plurality of magnetic domains whose magnetization directions are antiparallel to each other are formed in the isolated magnetic regions. A perpendicular magnetic recording medium is disclosed.

  A conventional example disclosed in Patent Document 3 will be described with reference to FIG. The description will be made particularly on the characteristic features of the prior art, and the portions that are widely known in the technical field may be omitted. In FIG. 4, 401 is a soft magnetic backing layer formed on a substrate (not shown), 402 is a nonmagnetic underlayer, 403 is a perpendicular magnetic recording layer, 404 is a magnetic area, 405 nonmagnetic area, 406 is a magnetic domain, and 407 is a recording. Magnetic head.

  This conventional example is applied to a disk-shaped perpendicular recording medium such as an HDD. Specifically, it is composed of a soft magnetic backing layer 401, a nonmagnetic underlayer 402, and a perpendicular magnetic recording layer 403 formed on a disk-like substrate (not shown) such as aluminum having mechanical properties that can withstand rotational motion by sputtering or the like. Perpendicular magnetic recording media. The perpendicular magnetic recording layer 403 is formed by patterning a plurality of magnetic regions 404 in a nonmagnetic region 405 by an electron beam drawing method or the like. The perpendicular magnetic recording layer 403 is often provided with a protective layer for protecting the same layer and a lubricating layer for smoothly sliding the recording magnetic head 407.

  The recording magnetic head 407 floats and slides at an interval of several tens to two hundred nanometers with respect to the medium surface by the rotation of the disk-shaped medium. A recording applied magnetic field is applied from the recording magnetic head 407 substantially perpendicular to the medium surface in accordance with the information data to be recorded.

  The recording applied magnetic field penetrates the perpendicular magnetic recording layer 403 and the nonmagnetic underlayer 402 perpendicular to the main magnetic pole perpendicularly to the film surface from the main magnetic pole of the recording magnetic head 407. Then, it passes through the soft magnetic underlayer 401 and passes through the nonmagnetic underlayer 402 and the perpendicular magnetic recording layer 403 at the sub magnetic pole position behind the main magnetic pole for recording 407 and reaches the sub magnetic pole of the recording magnetic head 407. As described above, since the substantially closed magnetic circuit is formed by the main magnetic pole and the sub magnetic pole of the recording magnetic head 407 and the soft magnetic backing layer 401 of the perpendicular recording medium, it is difficult for the applied magnetic field to diverge midway. As a result, the magnetic field strength in the perpendicular magnetic recording layer 403 is reduced, and the influence of diffusion of the magnetic field application region is suppressed.

  The soft magnetic backing layer 401 is provided for effective use of the applied magnetic field as described above. However, in order to suppress the occurrence of spike noise due to the domain wall in the soft magnetic backing layer 401, the magnetic anisotropy is easily generated in the plane. It is also possible to have a multilayer structure in which the axes are oriented or an antiferromagnetic film is included.

  In the magnetic region 404 of the perpendicular magnetic recording layer 403, the easy axis of magnetic anisotropy faces the direction perpendicular to the surface of the perpendicular magnetic recording layer 403, and the magnetization in the magnetic region 404 faces upward or downward depending on the recording information. Each magnetic region 404 is divided by a nonmagnetic region 405, and magnetic coupling such as magnetic exchange coupling is broken.

  Therefore, the magnetic regions 404 do not affect each other except through a demagnetizing field that is a magnetostatic interaction in which magnetization of the magnetic regions is generated. When the area density of the magnetic region 404 on the surface of the perpendicular magnetic recording layer 403 is small, the size of the magnetic pole appearing on the surface is small. For this reason, the magnitude of this demagnetizing field is small, and each magnetic region 404 can independently reverse the magnetization direction. Therefore, in general, a medium having a perpendicular magnetic recording layer structure in which such a magnetic region is separated by a nonmagnetic region is used for recording. The noise will be small.

  On the other hand, when the density of the magnetic region 404 on the surface of the perpendicular magnetic recording layer 403 is increased and the space between the magnetic regions 404 is reduced for the purpose of increasing the density, an external magnetic field such as a recording applied magnetic field is affected by the demagnetizing field. Even if no voltage is applied, the magnetization of the magnetic region 404 is reversed and the recorded information is easily destroyed.

  In Patent Document 3, the magnetic region 404 includes three magnetic domains 406, and the magnetizations in the respective magnetic domains are substantially aligned, but the magnetization directions of the magnetic sections are antiparallel. For this reason, the magnetic poles appearing on the surface are smaller in size than the configuration in which the magnetic region 404 is a single magnetic domain. Further, since the antiparallel magnetic domain regions are adjacent to each other, the static magnetic fields generated in the magnetic regions 404 cancel each other to form a magnetic closed magnetic circuit, and the influence of the demagnetizing field on the adjacent magnetic regions is small. As a result, even if the recording density is increased, the medium having excellent recording characteristics can be provided without increasing the influence of the demagnetizing field.

  However, in such a conventional technique, recording must be performed so that magnetic domains that are antiparallel to each other are formed in the magnetic region and reproduced as a signal. For example, in Patent Document 3, in order to record a signal of “1” (for example, an upward magnetization direction) in a certain magnetic region, a magnetic domain having a reverse magnetization direction needs to exist in the magnetic region adjacent to the magnetic region. There is. Therefore, “0” downward magnetization must be recorded before and after the “1” upward magnetization region. For this reason, it is necessary to change the signal processing method at the time of recording from the conventional one, and it cannot be applied as it is to the conventional HDD device.

  Furthermore, such conventional examples have the following problems when the magnetic region is made smaller for higher density. That is, in order to form a plurality of magnetic domains in the continuous magnetic material in the magnetic region, there is a magnetization direction variation region called a domain wall between the magnetic domains. The size of the domain wall is determined by the magnetic characteristics of the magnetic material. Generally, however, a plurality of magnetic domains with uniform magnetization directions cannot exist if the magnetic region is made smaller and the domain wall size (thickness) or less. For this reason, the size of the magnetic region is limited, and the configuration becomes inappropriate for high density.

  The relationship between the domain wall thickness σ and the magnetic material magnetic properties is described, for example, in Non-Patent Document 1 as shown in Equation 1 below.

  Here, A is the exchange constant of the magnetic material, K is the magnetic anisotropy energy density of the magnetic material, and c is a constant and depends on the direction of magnetization of the magnetic domain sandwiching the crystal or domain wall. When the direction of the 180-degree magnetization changes before and after, it is generally larger than π (circumference).

  When calculated from this equation (1), the domain wall thickness σ is about 10 nm or more in a general hard magnetic material for magnetic recording, and the magnetic anisotropy energy density is about one digit larger than that of a conventional magnetic material. Even the ordered alloy material has a value of about 4 nm or more. For this reason, in order to provide a plurality of magnetic domains having the same magnetization direction and a plurality of domain walls therebetween, the size of the magnetic region needs to be several tens of nanometers, particularly about 30 nm or more.

For this reason, even a simple calculation has a problem that the configuration is not suitable for a medium that performs high-density recording exceeding 1 terabit / square inch, which is a magnetic region of 25 nm square or less per bit. .
JP 2004-237429 A JP 2002-175621 A Japanese Patent Laid-Open No. 2003-030812 Keizo Ota, “Basics of Magnetic Engineering II” p. 272-273, Kyoritsu Publishing Co., Ltd., published in 1972

  In the prior art described in Patent Document 3, a special method must be used at the time of recording in order to form a plurality of magnetic domains in the magnetic region, and a recording method similar to that of a normal HDD device cannot be applied as it is. The process was complicated.

  Furthermore, since the conventional technique described in Patent Document 3 has a plurality of magnetic domains in the magnetic region, the boundary has a domain wall having a constant thickness, and the magnetization direction changes in the domain wall portion, so that it is not used as an effective recording region. The size of the magnetic region is limited. For this reason, there is a problem that the magnetic region cannot be reduced and it is difficult to increase the density.

  The present invention solves these problems and provides a high-density magnetic recording medium. In particular, in the magnetic recording medium having a structure in which the magnetic recording layer has a plurality of magnetic regions magnetically separated by a nonmagnetic material, an increase in the demagnetizing field of the magnetic recording layer is suppressed, and High density is achieved.

  A magnetic recording medium for solving the above problems is a magnetic recording medium having a magnetic recording layer in which a plurality of magnetic regions are independently provided in a base material made of a non-magnetic material, wherein the magnetic region is at least magnetic recording It is characterized by having at least one or more soft magnetic layers and hard magnetic layers in the in-plane direction, and having a nonmagnetic layer made of a nonmagnetic material between the soft magnetic layer and the hard magnetic layer.

Preferably, the magnetic region is provided with a nonmagnetic layer surrounding the hard magnetic layer around the hard magnetic layer, and a soft magnetic layer surrounding the nonmagnetic layer.
Preferably, the magnetic region is provided with a nonmagnetic layer surrounding the soft magnetic layer around the soft magnetic layer, and a hard magnetic layer is provided surrounding the nonmagnetic layer.

In the magnetic region, it is preferable that a nonmagnetic layer is provided with the hard magnetic layer sandwiched around the hard magnetic layer, and a soft magnetic layer is provided with the nonmagnetic layer sandwiched therebetween.
In the magnetic region, it is preferable that a nonmagnetic layer is provided with the soft magnetic layer sandwiched around the soft magnetic layer, and a hard magnetic layer is provided with the nonmagnetic layer sandwiched therebetween.

The average magnetic anisotropy energy density of the soft magnetic layer is preferably smaller than the average magnetic anisotropy energy density of the hard magnetic layer.
It is preferable that the magnetization directions of the soft magnetic layer and the hard magnetic layer are antiparallel when no external recording magnetic field is applied.

The magnetization directions of the soft magnetic layer and the hard magnetic layer are preferably parallel to the direction of the applied magnetic field when an external recording magnetic field is applied.
The magnetization direction of the soft magnetic layer is preferably antiparallel to the magnetization direction of the hard magnetic layer after an external recording magnetic field is applied.

The product of the cross-sectional area of the soft magnetic layer on the magnetic recording layer surface and the magnitude of the saturation magnetization is preferably smaller than the product of the cross-sectional area on the magnetic recording layer surface of the hard magnetic layer and the magnitude of the saturation magnetization.
The product of the cross-sectional area of the hard magnetic layer on the surface of the magnetic recording layer and the magnitude of the saturation magnetization is preferably smaller than the product of the cross-sectional area of the soft magnetic layer on the surface of the magnetic recording layer and the magnitude of the saturation magnetization.

  According to the present invention, a high-density magnetic recording medium can be provided. In particular, according to the present invention, in a magnetic recording medium having a structure in which the magnetic recording layer has a plurality of magnetic regions magnetically separated by a nonmagnetic material, an increase in the demagnetizing field of the magnetic recording film is suppressed, and Densification can be achieved.

Hereinafter, the present invention will be described in detail.
An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a magnetic recording medium according to the present invention. In the figure, 1 is a substrate, 2 is an underlayer, 3 is a soft magnetic underlayer, 4 is a nonmagnetic underlayer, 5 is a magnetic recording layer, 6 is a protective layer, and 7 is a lubricating layer.

  Here, a configuration in which the present invention is applied to an HDD disk-shaped medium will be described. In this case, as shown in FIG. 8, the magnetic recording medium 81 is read and written by a magnetic head 83, a magnetic head driving unit 84 for moving the magnetic head 83 to a desired recording position, a disk-like magnetic recording medium 81 by a motor, and the like. Can be incorporated into an HDD device including a magnetic recording medium driving unit 82 that rotates and a signal processing unit 85. However, the main configuration of the present invention can be applied to a magnetic recording layer of a general magnetic recording medium, and can be used for a medium having a perpendicular magnetic recording layer on a solid substrate. It is not limited to a rotating medium.

  The substrate 1 is made of glass, aluminum, a carbon substrate, a plastic substrate, a Si substrate, etc., and holds the upper layers. Other materials may be used for the substrate as long as they have mechanical characteristics that allow good recording of signals on the magnetic recording layer 5 and reproduction of magnetic signals from the same layer.

  The underlayer 2 is used to protect the upper layers from oxygen, moisture, etc. in order to remove the influence of the surface roughness of the substrate 1 and so on when the layers after the soft magnetic backing layer 3 are formed on the substrate 1. 1 for reinforcing the hardness and improving the adhesion with the upper layer. As long as the underlayer 2 achieves the above object, its material, film thickness, etc. can be freely taken. In general, NiP or the like is formed with a thickness of several nanometers to several hundred nanometers on the substrate 1 by a plating method or the like. Furthermore, an effect of controlling the magnetic characteristics of the soft magnetic backing layer 3 may be provided.

  The soft magnetic underlayer 3 converges magnetic flux in the magnetic recording layer 5 to increase the magnetic field strength and writes the magnetic field in the direction perpendicular to the recording film surface when information is written to the magnetic recording medium by the magnetic field generated by the recording magnetic head. It is provided for the purpose of alignment. In particular, using a monopole recording magnetic head for perpendicular magnetic recording, a closed magnetic circuit is formed by generating magnetic flux reflux at the recording magnetic pole (monopole) of the recording magnetic head, the soft magnetic underlayer 3, and the auxiliary magnetic pole of the recording magnetic head. As a result, good magnetic recording is performed. High magnetic permeability materials such as NiFe alloy (Permalloy) and amorphous soft magnetic materials such as FeTaC and CoZrNb can be used for converging magnetic flux, but other high magnetic permeability due to alignment with the upper film material. Materials may be used. Further, for the purpose of preventing spike noise due to the movement of the domain wall in the soft magnetic backing layer 3, a multilayer structure, use of an antiferromagnetic magnetic material, orientation control, and the like may be performed. When the film thickness is about 100 nanometers or less, the effect of magnetic flux convergence is reduced. However, when the film thickness is too thick, productivity and medium durability are deteriorated. Therefore, it is preferable to take about several hundred nanometers to several microns.

The nonmagnetic underlayer 4 is provided for the purpose of controlling the magnetic coupling between the soft magnetic underlayer 3 and the magnetic recording layer 5 and for the purpose of controlling the orientation during the formation of the magnetic recording layer 5.
The magnetic recording layer 5 is a recording film that records the direction of magnetization in accordance with the recording information signal in the direction perpendicular to the film surface. Since the feature of the present invention is mainly in the configuration of the magnetic recording layer 5, the configuration of the magnetic recording layer 5 will be described later with reference to FIG.

  The protective layer 6 is formed by depositing carbon, particularly diamond-like carbon (DLC), for the purpose of protecting the magnetic recording layer 5 from the upper lubricating layer 7, the outside air, and external impact on the medium surface.

  The lubricating layer 7 is used for improving the lubricity of the medium surface and the flying magnetic head for recording and reproduction by the flying magnetic head, and can be used for ordinary HDD media, such as PFPE (perfluoropolyether). .

  At the time of recording, a recording magnetic field in the direction perpendicular to the medium surface is applied from the floating magnetic recording head on the surface of the lubricating layer 7 to the perpendicular magnetic medium. A magnetic recording head called a monopole head is preferable because the recording magnetic field converges and the recording magnetic field can be efficiently applied to the magnetic recording layer 5. The flying magnetic recording head floats and slides on the surface of the lubricant layer 7 with a flying height of several tens of nanometers, and generates a magnetic field from the main pole in a direction substantially perpendicular to the perpendicular magnetic medium. The generated magnetic field passes through the gap between the magnetic recording head and the surface of the lubricating layer 7, the lubricating layer 7, and the protective layer 6, and changes the magnetization of the recording portion in the magnetic recording layer 5 in a predetermined recording direction (up and down direction perpendicular to the medium surface). To the soft magnetic backing layer 3 through the nonmagnetic underlayer 4. The magnetic field parallel to the film surface due to the high magnetic permeability of the soft magnetic underlayer 3 crosses the nonmagnetic underlayer 4, the magnetic recording layer 5, the protective layer 6, and the lubricating layer 7 behind the magnetic recording head. It reaches the sub magnetic pole behind the main magnetic pole of the recording head.

  FIG. 2 is a diagram showing the configuration of the magnetic recording layer in the first embodiment for carrying out the present invention. In FIG. 2, 5 denotes a magnetic recording layer as in FIG. 22 is a magnetic region, 21 is a nonmagnetic material that magnetically separates each magnetic region 22, 23 is a soft magnetic layer constituting the magnetic region 22, 23 is a nonmagnetic layer constituting the magnetic region 22, and 25 is a magnetic region 22. Is a hard magnetic layer. The magnetic region 22 according to this embodiment of the present invention is characterized by at least two magnetic layers extending inward and outward in the radial direction of the magnetic region 22 in the in-plane direction of the magnetic recording layer and the nonmagnetic layer 24 therebetween. The magnetic layers are composed of a soft magnetic layer 23 and a hard magnetic layer 25, respectively. A feature of the plurality of magnetic regions 22 according to the present invention is that they are magnetically separated in the direction of the magnetic recording layer surface.

  The first embodiment for carrying out the present invention has a nonmagnetic layer 24 along the outer diameter of the cylindrical magnetic body structure having the hard magnetic layer 25 as an inner diameter, and further has a magnetic recording layer 5 surface along the outer diameter. The soft magnetic layer 23 is provided in the inward direction. The in-plane direction of the magnetic recording layer indicates an arbitrary direction parallel to the film surface of the magnetic recording layer and is, for example, a direction represented by an arrow 8 in FIG.

  The magnetic layer constituting the magnetic region of the present invention is not limited to the two layers of the hard magnetic layer 25 and the soft magnetic layer 23 shown in FIG. 2, and a multilayer structure of hard magnetic material and soft magnetic material can be used. A feature of the present invention is that the magnetic material in the magnetic region has a multilayer structure of a hard magnetic layer made of a hard magnetic material and a soft magnetic layer made of a soft magnetic material in the in-plane direction of the magnetic recording layer, and the hard magnetic material layer and the soft magnetic material It is to provide a nonmagnetic material layer at the boundary of the layers.

  By taking a multilayer structure and changing the magnetic characteristics in each layer, there is an advantage that the magnetic characteristics in the magnetic region can be adjusted. However, when the hard magnetic material layer and soft magnetic material layer are composed of multiple layers, the production process becomes complicated, and a nonmagnetic layer is provided at each boundary. Is disadvantageous.

The magnetic anisotropy energy density and saturation magnetization of the soft magnetic layer and the hard magnetic layer may have a distribution depending on the location in each layer.
The difference between the soft magnetic layer 23 and the hard magnetic layer 25 according to the present invention depends on the average magnetic anisotropy energy density of the corresponding layer. The soft magnetic layer according to the present invention means a layer in which the average magnetic anisotropy energy density of the corresponding layer is smaller than the average magnetic anisotropy energy density of the hard magnetic layer. The average magnetic anisotropy energy means that the soft magnetic layer 23 and / or the hard magnetic layer 25 has a multilayer structure composed of multiple layers, or in each layer of the soft magnetic layer 23 and / or the hard magnetic layer 25. It means the average value of the magnetic anisotropy energy density taken for each of the soft magnetic layer 23 and / or the hard magnetic layer 25 when the magnetic anisotropy energy density has a distribution depending on the location.

  The difference in average magnetic anisotropy energy density and average saturation magnetization may be due to the difference in constituent elements of the constituent materials of the soft magnetic layer and the hard magnetic layer. The difference between the average magnetic anisotropy energy density and the average saturation magnetization may be due to the difference in the composition ratio of the constituent elements of the soft magnetic layer and the hard magnetic layer. The difference in average magnetic anisotropy energy and average saturation magnetization may be due to the difference in crystal structure of the constituent materials of the soft magnetic layer and the hard magnetic layer. Further, the difference between the average magnetic anisotropy energy density and the average saturation magnetization may be caused between the soft magnetic layer and the hard magnetic layer by the above combination.

  The effect of suppressing the generation of the demagnetizing field near the magnetic recording layer 5 according to the present invention will be described with reference to FIG. FIG. 5A is a schematic cross-sectional view around one magnetic region of a magnetic recording medium in which a magnetic region embedded in a nonmagnetic material is composed only of a hard magnetic material. FIG. 5B is a schematic cross-sectional view of the arrangement of the magnetization of one magnetic region 22 and its surroundings in the present invention. 2, 24, and 25 represent the soft magnetic layer 23, the nonmagnetic layer 24, and the hard magnetic layer 25 as in FIG. 2, and 26 schematically represents the magnetic flux lines of the magnetic field generated by the magnetic region 22. FIGS. 5A and 5B both show the case where the hard magnetic layer 25 of the hard magnetic material portion that carries magnetic information is magnetized upward.

  In the magnetic recording medium of FIG. 5A, the magnetic region is uniformly magnetized upward, so that the magnetic poles are excited on the upper and lower surfaces of the magnetic recording layer 5 in the region, and the demagnetizing field is thereby generated in the magnetic recording layer 5. Occurs near the surface. Since this demagnetizing field generally does not attenuate to a relatively wide area in the plane direction of the magnetic recording layer 5, in general, a certain magnetic area receives a demagnetizing field from other surrounding magnetic areas. . For example, when the magnetization direction of a certain magnetic region is antiparallel to the direction of the sum of the demagnetizing fields from the surrounding magnetic regions, the magnetization direction of the magnetic region is easily reversed, and the recording retention capability is lowered. In addition, the magnetization direction is easily reversed when a recording magnetic field is applied. On the other hand, when the magnetization direction of the magnetic region is parallel to the direction of the total demagnetizing field from the surrounding magnetic regions, the magnetization direction is not easily reversed even when a recording magnetic field is applied. Since the magnitude of the demagnetizing field felt in the magnetic region is determined by the direction of magnetization of each surrounding magnetic region, it is influenced by the direction of magnetization of each of the other magnetic regions existing in a wide range.

  For this reason, during recording, recording noise is generated due to the disturbance of the demagnetizing field due to the magnetization direction of each of the surrounding magnetic regions in addition to the magnetic field applied to the recording magnetic head. In addition, even during non-recording, variations in the record holding ability are caused by such variations in the demagnetizing field.

  On the other hand, in the present invention, as shown in FIG. 5B, the magnetic region 22 is composed of a soft magnetic layer 23, a nonmagnetic layer 24, and a hard magnetic layer 25, and among these, the magnetization of the soft magnetic layer 23 and the hard magnetic layer 25. The directions are perpendicular to the surface of the magnetic recording layer 5 and antiparallel to each other. For this reason, the demagnetizing fields generated by the respective magnetizations of the soft magnetic layer 23 and the hard magnetic layer 25 cancel each other, and the magnetic force lines 26 are refluxed on the surfaces of the magnetic recording layer 5 of the soft magnetic layer 23 and the hard magnetic layer 25. Therefore, the demagnetizing field generated by the magnetic region 22 decreases rapidly with respect to the distance in the film surface direction of the magnetic recording layer 5. For this reason, when focusing on a certain magnetic region, the influence of the demagnetizing field generated from the magnetic region far from the magnetic region is reduced. As a result, the value of the demagnetizing field bias applied to the magnetic region becomes small, and at the same time, the range of the surrounding magnetic region that affects the magnetic region becomes small. This suppresses recording noise that occurs during recording. Further, since the demagnetizing field bias applied to the magnetic region 22 is small in variation and non-recording, the variation in the recording retention capability is suppressed, and the recording retention in the entire recording medium is made uniform.

  Of the magnetic field from the magnetization of the hard magnetic layer 25 that becomes the reproduction signal, the intensity in the upper direction of the magnetic region 22 is offset by the magnetic field from the magnetization of the soft magnetic layer 23 and the intensity drops, but the intensity just drops. Then the offset is relatively small. For this reason, the planar intensity distribution of the reproducing magnetic field on the surface of the magnetic recording layer 5 becomes sharper, and the planar resolution of the reproducing magnetic field distribution during reproduction is improved. For this reason, in this structure, the edge of the reproduction magnetic field distribution can be easily detected for magnetic signal reproduction, and as a result, the reproduction signal quality is improved.

  In particular, it is not preferable to increase the thickness of the soft magnetic layer in the in-plane direction of the magnetic recording layer in order to prevent the reproduction signal intensity from being deteriorated by the magnetic field from the soft magnetic layer 23 having antiparallel magnetization to the hard magnetic layer 25. This thickness depends on the magnitude of the magnetization of the soft magnetic layer 23, etc., and the product of the cross-sectional area of the hard magnetic layer 25 on the surface of the magnetic recording layer 5 and the magnitude of the saturation magnetization Ms, and the magnetic recording layer of the soft magnetic layer 23. The product of the cross-sectional area at the five planes and the magnitude of the saturation magnetization Ms is approximately the same as the size of the magnetic pole excited on the surface of the magnetic recording layer 5. A magnetic field due to the magnetization direction of the hard magnetic layer 25 that is a reproduction signal for the entire magnetic region 22 is detected by the reproduction head. For this purpose, the thickness of the soft magnetic layer 23 is set so that the product of the cross-sectional area of the soft magnetic layer 23 on the surface of the magnetic recording layer 5 and the magnitude of the saturation magnetization Ms is the cross-sectional area of the hard magnetic layer 25 on the surface of the magnetic recording layer 5. And half the product of the magnitudes of the saturation magnetization Ms. By increasing the thickness of the soft magnetic layer 23 and the saturation magnetization Ms, the demagnetizing field suppressing effect is enhanced, but the reproduction signal intensity is decreased. Preferably, the product (A) of the cross-sectional area of the soft magnetic layer 23 on the surface of the magnetic recording layer 5 and the magnitude of the saturation magnetization Ms, and the cross-sectional area of the hard magnetic layer 25 on the surface of the magnetic recording layer 5 and the magnitude of the saturation magnetization Ms. The ratio of the product (B) is preferably about A: B = 1: 10 to 1: 2.

  The first feature of the magnetic region 22 of the present invention is that a region having anti-parallel magnetization directions in the magnetic region 22 at the time of recording and holding is divided into a soft magnetic layer 23 and a hard magnetic layer 25 having different average magnetic anisotropy energy densities. And is composed of The operation of the magnetic region 22 of the present invention resulting from such a configuration will be described below.

  The state of magnetization reversal during recording of the magnetic region 22 during recording will be described with reference to FIG. FIG. 6A schematically shows the state of magnetization in one magnetic region 22 in the magnetic recording layer 5 before application of the recording magnetic field. Here, it is assumed that the magnetic region 22 is recorded so that the magnetization direction is upward in the figure. Correspondingly, the magnetization direction of the hard magnetic layer 25 inside the magnetic region 22 is directed upward in the figure, and the soft magnetic layer 23 located outside is oriented downward in the figure. The hard magnetic layer 25 and the soft magnetic layer 23 face each other in anti-parallel magnetization directions, thereby canceling out magnetic poles generated on the surface of the magnetic recording layer, thereby preventing the generation of a demagnetizing field near the surface of the magnetic recording layer.

  In order to perform magnetic recording on the magnetic region 22, a recording magnetic field is applied in a direction perpendicular to the medium surface of the medium by a recording head (not shown). Here, assuming that a recording magnetic field Hext is applied in the direction opposite to the direction recorded first, and in the downward direction in the figure, the recording magnetic field Hext causes the hard magnetic layer 25 and the soft magnetic layer 23 to move as shown in FIG. The magnetization directions are parallel and the magnetization is directed downward in the figure.

  When the recording magnetic field Hext from the magnetic head disappears, the arrangement shown in FIG. Since the hard magnetic layer 25 has a high magnetic anisotropy energy density, it maintains the magnetization direction. On the other hand, since the soft magnetic layer 23 has a lower magnetic anisotropy energy density than the hard magnetic layer 25, the magnetization direction is reversed by the demagnetizing field generated by the hard magnetic layer 25, and the hard magnetic layer 25 is opposite to the magnetization direction. It will face the parallel direction. As a result, the magnetization direction of the hard magnetic layer 25 on the inner side of the magnetic region 22 is directed downward in the figure, and the soft magnetic layer 23 on the outer side is oriented upward in the figure in the opposite direction to FIG. The hard magnetic layer 25 and the soft magnetic layer 23 face anti-parallel magnetization directions. This cancels out the magnetic poles generated on the surface of the magnetic recording layer, and the demagnetizing field generated on the surface of the magnetic recording layer becomes a small value.

  When the direction of the recording magnetic field from the recording head is applied in the same direction as the magnetization direction of the initial magnetic region 22 shown in FIG. 6A, for example, when the recording magnetic field is applied in the upward direction according to FIG. Due to the applied recording magnetic field, the magnetizations of the hard magnetic layer 25 and the soft magnetic layer 23 are aligned in parallel and face upward in the figure. Similarly, after the magnetic field applied from the recording head disappears, only the magnetization direction of the soft magnetic layer 23 is reversed due to the difference in magnitude of magnetic anisotropy energy between the hard magnetic layer 25 and the soft magnetic layer 23, as shown in FIG. ) Stable in the magnetization direction arrangement. As a result, generation of a demagnetizing field in the vicinity of the surface of the magnetic recording layer 5 is suppressed by the magnetization of the hard magnetic layer 25 and the soft magnetic layer 23 which are settled in the initial state shown in FIG.

  As described above, in the present invention, since the soft magnetic layer 23 having a low magnetic anisotropy energy density is provided around the hard magnetic layer 25 having a high magnetic anisotropy energy density, the soft magnetic layer 23 having a low magnetic anisotropy energy density is provided. The magnetization direction of the magnetic layer 23 is naturally antiparallel to the magnetization direction of the hard magnetic layer 25. For this reason, it is not necessary to align the magnetization direction of the soft magnetic layer 23 antiparallel to the magnetization direction of the hard magnetic layer 25 using external means such as a recording applied magnetic field, and when no external magnetic field is applied. Automatically obtains an antiparallel magnetization arrangement as shown in the figure. As a result, an antiparallel magnetization arrangement as shown in the figure is automatically formed in the magnetic region 22 without changing the recording signal to the recording head or using a recording method different from the conventional one using external means. . This has the advantage that generation of a demagnetizing field near the surface of the magnetic recording layer 5 is suppressed.

  The second feature of the magnetic region 22 of the present invention is that the magnetic coupling, more precisely the magnetic exchange coupling between the soft magnetic layer 23 and the hard magnetic layer 25 which have antiparallel magnetization directions at the time of recording and holding is cut off. The magnetic layer 24 is provided.

  The effect of the nonmagnetic layer 24 will be described with reference to the drawings. FIG. 7A shows the vicinity of the interlayer junction when the nonmagnetic layer 24 is not provided between the soft magnetic layer 23 and the hard magnetic layer 25 and the magnetization directions of the soft magnetic layer 23 and the hard magnetic layer 25 are antiparallel. It is a schematic diagram of the magnetization direction distribution in FIG. The magnetization in the soft magnetic layer 23 and the hard magnetic layer 25 tends to align the directions of adjacent magnetizations by the magnetic exchange coupling interaction of the ferromagnetic material. Due to this exchange coupling interaction, the magnetization direction of the soft magnetic layer 23 having a small magnetic anisotropy energy density, particularly in the vicinity of the boundary with the hard magnetic layer 25, tends to be aligned with the magnetization direction of the hard magnetic layer 25. For this reason, it is difficult to immediately make the magnetization direction antiparallel at the boundary between the soft magnetic layer 23 and the hard magnetic layer 25, and the soft magnetic layer 23 has a region having a magnetization direction antiparallel to the magnetization direction of the hard magnetic layer 25. For this purpose, a transition region in which the direction of magnetization continuously changes from the boundary surface is required. This transition region is called a domain wall, and the thickness of the domain wall can be estimated from the magnetic properties of the almost magnetic material.

  If the calculation is performed for a typical soft magnetic material according to the above-described equation 1, the domain wall thickness is about 100 nm to several μm. For this reason, when the magnetic region 22 needs to have a size of about several tens of nanometers on the surface of the magnetic recording layer 5 for high-density recording, when the soft magnetic layer 23 is to be provided in the magnetic region 22. Since the thickness of the soft magnetic layer 23 is thin, a domain wall cannot be formed, and the magnetization direction of the soft magnetic layer 23 cannot be made antiparallel to the magnetization direction of the hard magnetic layer 25. Even when the soft magnetic layer 23 is formed in the magnetic region 22 of 100 nm or more on the surface of the magnetic recording layer 5, the magnetic field generated from the domain wall portion in the soft magnetic layer 23 has the effect of canceling the magnetic field from the hard magnetic layer 25. weak. In order to suppress the demagnetizing field of the magnetic recording layer 5, a further soft magnetic layer 23 is required. Therefore, in order to obtain the effect of suppressing the demagnetizing field with such a configuration, the size of the magnetic region 22 is approximately submicron. And cannot be applied to high-density recording.

  More specifically, the thickness of the domain wall is about 10 nm or more even for a hard magnetic material, and about 4 nm or more for an ordered alloy material of FePt and FePd whose anisotropy constant is said to be about an order of magnitude larger than that of a conventional magnetic material. Therefore, a domain wall of several nm to 10 nm is also generated in the hard magnetic layer 25. For this reason, the reproducing magnetic field from the hard magnetic layer 25 is reduced, and the record holding ability of the hard magnetic layer 25 is reduced.

  On the other hand, in the configuration of the present invention shown in FIG. 7B, since the nonmagnetic layer 24 is provided between the soft magnetic layer 23 and the hard magnetic layer 25, the magnetic layer between the soft magnetic layer 23 and the hard magnetic layer 25 is magnetic. Exchange coupling interactions do not work. For this reason, the magnetization direction of the soft magnetic layer 23 can be made independent of the magnetization direction of the hard magnetic layer 25 (from the viewpoint of magnetic exchange coupling) from near the boundary with the nonmagnetic layer 24. In addition, the magnetic field generated by the hard magnetic layer 25 is affected, and the magnetic direction of the hard magnetic layer 25 can be favorably antiparallel.

  The thickness of the nonmagnetic layer 24 is not limited as long as the magnetic exchange coupling between the soft magnetic layer 23 and the hard magnetic layer 25 can be broken, and the magnetic exchange coupling is basically caused by the interaction between atoms of the magnetic material. In principle, it is only necessary that several atomic layers of nonmagnetic atoms exist at the boundary. Actually, it is sufficient that the thickness is 1 nm or more and several nm or less for the convenience of preparation, and the magnetic region 22 having a thickness of 100 nm or less can be formed because it can be formed with an extremely thin film thickness compared with the thickness of the domain wall without the nonmagnetic layer 24. However, the soft magnetic layer 23 and the hard magnetic layer 25 having a thickness of several tens of nm can be sufficiently formed in the region.

Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
In this example, a hard magnetic layer 25 having a substantially cylindrical shape is formed by combining a hard magnetic material into a large number of holes in the porous member, and the base material of the porous member is removed to remove the hard magnetic layer 25 from the outside. After the magnetic layer 24 and the soft magnetic layer 23 are formed, the space between the magnetic layer 24 and the soft magnetic layer 23 is filled with a non-magnetic material to create the embodiment shown in FIG.

  The main point of this embodiment is mainly related to the configuration of the magnetic recording layer 5. The substrate 1, which is the lower structure of the magnetic recording layer 5, the soft magnetic backing layer 3, the protective layer 6 and the lubricating layer 7 of the upper structure are as follows. It can be created by a production method similar to that of a conventional HDD perpendicular recording medium. Since the nonmagnetic underlayer 4 may be used as the underlayer for the magnetic recording layer 5 when the magnetic recording layer 5 is formed, the following description will be mainly made with respect to the magnetic recording layer 5 and the nonmagnetic underlayer 4.

  First, a porous member constituting the nonmagnetic underlayer 4 and later the magnetic recording layer 5 is formed on the soft magnetic backing layer 3. This is called a porous member creation step. Next, the hard magnetic material constituting the hard magnetic layer 25 is combined in the hole of the porous member. This is called a hard magnetic material combining step. Next, a part of the base material portion of the porous member is removed to expose the hard magnetic material portion. This is called a porous base material removing step. Next, a nonmagnetic material constituting the nonmagnetic layer 24 is laminated on the exposed hard magnetic material portion. This is called a nonmagnetic material coating process. Further, a soft magnetic material constituting the soft magnetic layer 23 is laminated on the nonmagnetic material. This is called a soft magnetic material coating step. Further, a hard magnetic material portion wrapped with a soft magnetic material constituting the magnetic region is embedded with a nonmagnetic material. This is referred to as a process of embedding in a nonmagnetic material. Finally, the surface portion is shaped to form the magnetic recording layer 5. This is called a magnetic recording layer surface shaping step.

  The hard magnetic material may be a general hard magnetic material having a high magnetic anisotropy energy density, but particularly high magnetic anisotropy by using any of FePt, FePd, CoPt, and CoPd having an L10 ordered structure. Sexual energy density can be secured. In this case, it is preferable to include a step of bringing the material into L10 ordering by heat treatment after the material is combined in the pores of the porous member.

  The soft magnetic material may be a general soft magnetic material having low magnetic anisotropy energy and high saturation magnetization Ms, and NiFe alloy (permalloy) or the like can also be used. Further, the soft magnetic layer 23 having a small magnetic anisotropy energy density may be formed by using a metal material having the same kind of Fe, Co, Pt, or Pd as the hard magnetic layer 25 and not being ordered. it can.

  The nonmagnetic material may be any nonmagnetic material, but in this embodiment, the soft magnetic layer 23 is formed by plating, and therefore, noble metals such as Pt and Pd that are conductive and can be used as a catalyst during plating are preferable.

Hereinafter, each step will be described in more detail with reference to FIG.
First, the nonmagnetic underlayer 4 is formed on the soft magnetic backing layer 3. The nonmagnetic underlayer 4 preferably has an orientation control function so that the magnetic recording layer 5 becomes a magnetic recording layer. In addition, when the electroplating method is used in the nonmagnetic material coating step, the nonmagnetic underlayer 4 is used as a part of the electrode, so that conductivity is required.

  On the other hand, if the soft magnetic material directly adheres to the non-magnetic underlayer 4 during the soft magnetic material coating process, the magnetic regions will be magnetically coupled later, which is not preferable for the recording characteristics of the magnetic recording layer 5. For this reason, the nonmagnetic underlayer 4 is made conductive, and a part of the base material in the vicinity of the magnetic recording layer 4 is left when the base material is removed in the porous base material removing step when electrolytic plating is performed in the soft magnetic material coating step. There is a need.

  In order to control the orientation, it is possible to insert an (001) oriented orientation control layer such as MgO into the nonmagnetic underlayer 4 and further provide an electrode layer for plating on the orientation control layer. It is also possible to use ZnO or the like that plays both roles of orientation control and electrode layer. Here, the orientation of the base electrode layer is preferably (001) in order to control the orientation of the magnetic material filling the hole.

  In particular, when an L10 ordered alloy having a large magnetic anisotropy energy density is used as the hard magnetic material of the present invention, the base electrode layer is used to orient the c-axis of the L10 ordered alloy layer in the magnetic material in the direction perpendicular to the substrate. It is preferable to have a tetragonal crystal arrangement parallel to the substrate surface. In particular, it is preferable to use the (001) orientation of the fcc structure.

  For example, the bottom layer of the nonmagnetic underlayer 4 is an orientation control layer such as oriented MgO, and a nonmagnetic underlayer 4 is obtained by epitaxially growing a Pt or Pb film having (001) orientation based on the orientation control layer. This is also a preferred form. For the orientation control, c-axis oriented ZnO or the like can also be used. Here, in order to control the orientation of the magnetic material filling the hole, it is preferable to use a material having an fcc structure for the underlayer and to make the (111) or (001) orientation, and the most preferred is the (001) orientation. .

  In order to prevent these metals from diffusing into the soft magnetic underlayer 3 when the nonmagnetic underlayer 4 contains Pt or Pd, a protective layer made of Ti or the like is used with the lower layer portion of the nonmagnetic underlayer 4 as an undercoat layer. It can also be configured.

Next, the porous member creation process will be described.
First, a film layer that will later constitute the magnetic recording layer 5 is formed on the nonmagnetic underlayer 4, and a plurality of holes are formed in the film surface.

  FIG. 3A shows a porous member 300 having a plurality of holes. The thickness of the porous member 300 is equal to or greater than that of the magnetic recording layer 5. The magnetic recording layer 5 was about 100 nm or less, preferably 50 nm or less, more preferably 30 nm or less, and more preferably 5 nm or more and 30 nm or less. For this reason, the film thickness can be further adjusted, and the thickness of the formed structure surface can be adjusted by etching or the like as a subsequent process, but the thickness of the magnetic recording layer 5 is preferably set to about 5.

  When the member is viewed from the upper surface side of the hole, the holes are dispersed as shown in FIG. 3 and 9, 301 is a hole, and 302 is a hole wall interposed between the holes. Holes are dispersedly arranged in the hole wall portion and may be expressed as a base material (or matrix portion). The hole 301 in FIG. 3 penetrates the nonmagnetic underlayer 4.

  In the porous member 300, the holes 301 of the porous member 300 are columnar holes, and the average diameter of the plurality of holes is about the diameter of the hard magnetic layer 25. From the viewpoint of reducing the “thermal fluctuation” effect and increasing the recording density, the diameter is preferably 2 nm or more and 30 nm or less.

  For example, as described in JP-A-2004-237429, the porous member 300 forms holes by anodizing aluminum or an alloy containing aluminum in a solution such as oxalic acid or phosphoric acid. It is obtained by doing. According to this method, a porous body having alumina as an oxide on the pore wall is formed.

  Further, for example, as described in JP-A-2002-175621, a structure in which columnar members are dispersed in a region surrounding the material is formed using a material forming a phase separation structure, and the columnar members A porous layer can be obtained by removing.

  Using a template having a pore diameter of 1 nm to 100 nm, particularly a diameter of 1 nm to 30 nm, particularly a diameter of 1 nm to 15 nm, and an average interval between holes of 20 nm or less in the form used in this embodiment, Useful for creating combined structures.

  Moreover, since the depth of the hole (thickness in the longitudinal direction of the hole) can be suitably formed to a depth of 5 nm or more and 100 nm or less, particularly 50 nm or less, more preferably 30 nm or less, the hole penetrating the magnetic recording layer 5 film thickness. The depth can be suitably configured.

In the following, an example based on the method described in Japanese Patent Application Laid-Open No. 2002-175621 will be described in more detail.
Specifically, a structure in which the periphery of the columnar member is surrounded by a region made of another material is prepared, and the columnar member is selectively removed. The structure is a structure in which the material constituting the region is contained in a ratio of 20 atomic% to 70 atomic% with respect to the total amount of the material constituting the columnar member and the material constituting the region. . If it is the range of the said ratio, the structure which the columnar member disperse | distributed to the matrix area | region which surrounds it is implement | achieved. Here, examples of the constituent material of the columnar member include Al and Mg. Examples of the material constituting the region surrounding the columnar member include Si, Ge, and a mixture of Si and Ge (hereinafter, sometimes referred to as Si _x Ge _1-x (0 <x <1)). It is done.

  In order to obtain a structure in which such columnar members are dispersed in a region surrounding them, non-equilibrium film formation such as sputtering using a target including both the columnar member and the material constituting the region surrounding the columnar members is provided. Realized by law. This will be described more specifically in the examples described later.

After the film formation, the columnar member is selectively removed. For example, when the columnar member is Al, by immersing it in ammonia water diluted to 2.8%, the Al portion is eluted and a porous material is formed. In addition, various acid solutions can also be used. The matrix portion is oxidized after the Al columnar member is melted to become SiO ₂ or GeO ₂ and a mixture of SiO ₂ and GeO ₂ .

Next, the hard magnetic material filling step will be described.
In the first creation method, a hard magnetic material is filled into the plurality of holes of the porous member 300. FIG. 3B shows a structure in which the inner filling material 303 is filled in the holes 301 and excess filling material is removed by polishing or the like.

  The filling 303 is a hard magnetic material having a large magnetic anisotropic energy density. For example, CoCrPt or the like can be filled by a dry process such as a sputtering method, a CVD method, a vapor deposition method, or a plating method. It is preferable to fill the L10 ordered alloy FePt, FePd, CoPt, CoPd, etc. having a larger magnetic anisotropy energy density.

  At this time, the method having the best filling property is a plating method. The nonmagnetic underlayer 4 contains Pt or Pd and other conductive metal components. Depending on the material to be filled with the nonmagnetic underlayer 4 as an electrode, Pt and Pd raw materials included hexachloroplatinum (IV) acid salt and hexachloroPd acid salt, and Fe and Co raw materials each including chloride and sulfate. Electrolytic plating may be performed using a plating solution.

  In addition, since Fe ions in the plating bath are relatively unstable and easily form precipitates, a complexing agent may be added to stabilize the Fe ions. The complexing agent is appropriately selected from tartaric acid, citric acid, succinic acid, malonic acid, malic acid, gluconic acid, and salts thereof. In particular, it is preferable to use tartaric acid or a salt thereof and / or citric acid or a salt thereof, and sodium tartrate and / or ammonium tartrate.

  Moreover, in order to suppress the time-dependent change of hexachloroplatinum (IV) acid salt, it is also effective to use a solution containing excessive Cl- ions such as NaCl. If necessary, ammonium ions may be added to form a complex of ammonium hexachloroplatinate (IV) to further promote stabilization in the solution.

  The ratio of the raw material added to the plating solution and the plating potential are controlled so that the Fe or Co composition and the Pt and Pd compositions are substantially equivalent and the L10 ordered composition. Since FePt, FePd, CoPt, and CoPd immediately after filling are generally not L10 ordered, a heat treatment process in which L10 ordering proceeds by performing heat treatment at 400 ° C. to 650 ° C. for several tens of minutes to several hours at this stage. Is preferred. The heat treatment is preferably performed in a reducing atmosphere, a vacuum, or a hydrogen atmosphere. It is particularly preferable to perform heat treatment in a hydrogen atmosphere.

  On the other hand, it is also possible to use a dry process such as sputtering, CVD, or vapor deposition for filling. In particular, the arc plasma gun is a technique close to ion plating for forming ionized metal particles, and has been proved to be a film forming technique excellent in embedding performance in the formation of wiring such as damascene. Further, the filling property is improved by applying the substrate bias.

  In addition, for example, ion beam sputtering is also a method suitable for embedding in a hole, in which deposited particles are scattered with good straightness with respect to the substrate. However, when a dry process is used, the film is formed not only in the hole but also on the hole wall, so that the filling property may be deteriorated. Therefore, when a dry process is used for filling the hard magnetic material of this embodiment, when the diameter of the hard magnetic layer 25 is 50 nm or less, the aspect ratio represented by (magnetic recording layer thickness) / (hard magnetic layer) is 2. It is preferable to apply to the following. More preferably, the dry process can be suitably applied to an aspect ratio of 1 or less. Further, if necessary, the filling property can be improved by alternately performing the step of removing the deposit on the hole wall by the etching process and the filling step.

It is preferable to remove the portion overflowing in the filling step by a technique such as polishing.
Next, the porous base material removing step will be described.
FIG. 3C shows a structure in which a part of the base material is removed in the porous base material removing step.

  The base material 302 is alumina when aluminum anodization is used in the process of FIG. 3A, and is Si or Ge, or an oxide of Si or Ge when a phase separation structure is used. It can be removed with a solution or hydrogen fluoride. By controlling the type, concentration, temperature, etc. of the solution, it is possible to control the dissolution rate and amount of the base material, and it is possible to leave a part of the base material as shown in FIG. is there. As shown in FIG. 3C, the inclusion filling 303 in the hole 301 is exposed to form a protruding structure 304, and the remaining base material remaining 305 covers the nonmagnetic underlayer 4 between the protruding structures 304. It remains.

  Through this step, a projecting structure 304 protruding upward is formed. The protruding structure 304 is a hard magnetic material, particularly preferably an L1 ordered FePt, FePd, CoPt, or CoPd alloy.

  This is used as a hard magnetic layer 25, and a nonmagnetic layer 24 and a soft magnetic layer 23 are sequentially formed thereon. The nonmagnetic layer 24 and the soft magnetic layer 23 can be formed by coating a metal nonmagnetic material and a soft magnetic material, respectively, by plating.

Next, the nonmagnetic material coating process and the soft magnetic material coating process will be described.
Pt, Pd or the like is used as the material of the nonmagnetic layer 24, and a film such as Pt or Pd is formed on the protruding structure 304 by electrolytic plating using the nonmagnetic underlayer 4 and the protruding structure 304 as an electrode. The nonmagnetic layer 24 is used. The space between the protruding structures 304 is covered with a base material remaining part 305 that has been removed by the porous base material removing step. Therefore, the plating solution and the nonmagnetic underlayer 4 that is an electrode are not in direct contact, so that no Pt or Pd film is formed, and only the exposed portion of the hard magnetic layer 25 is exposed to the nonmagnetic layer 24 as shown in FIG. Is formed. In FIG. 3C, the protruding structure 304 constituted only by the hard magnetic layer 25 becomes a protruding structure 306 covered with the nonmagnetic layer 24.

The electrolytic plating may be performed using a plating solution containing hexachloroplatinum (IV) acid salt or hexachloro Pd acid salt. In particular, when Pt is used as the nonmagnetic underlayer 4, it is also effective to use a solution containing excessive Cl ^- ions such as NaCl in order to suppress the change with time of the hexachloroplatinum (IV) acid salt. If necessary, ammonium ions may be added to form a complex of ammonium hexachloroplatinate (IV) to further promote stabilization in the solution.

  Further, the soft magnetic layer 23 is laminated on the projecting structure 306 by coating the soft magnetic material by electrolytic plating using the nonmagnetic underlayer 4 and the projecting structure 306 as an electrode. Plating is performed using permalloy as a soft magnetic material. For example, electrolytic plating may be performed using a plating solution in which boric acid as a buffer, sodium saccharin as an additive, sodium laurate as a surfactant, and the like are added to a mixed solution of nickel sulfate, nickel chloride, and iron sulfate. The composition ratio of permalloy Fe and Ni can be controlled mainly by the voltage and the iron sulfate component in the plating solution.

  In this way, as shown in FIG. 3E, the protruding structure 307 in which the protruding structure 306 is covered with the soft magnetic layer 23 is formed. Since the nonmagnetic underlayer 4 is covered with the base material remainder 305 in the same manner as the nonmagnetic material coating step and does not come into direct contact with the plating solution, the magnetic material does not adhere between the protruding structures 307. The protruding structures 307 are not magnetically coupled.

  The thicker the soft magnetic layer 23 to be plated is, the higher the effect of canceling the demagnetizing field from the hard magnetic layer 25 is. However, the thicker the soft magnetic layer 23 is, the larger the magnetic area is. Is not preferable. Although depending on the balance with the demagnetizing field canceling effect, it is desirable to set the radius of the hard magnetic layer 25 to about or less. When the size of the magnetic region is 10 nm or more and about 40 nm or less, the thickness of the soft magnetic layer 23 is preferably about several nm to 10 nm, and this thickness is a thickness sufficiently covered with plating.

Finally, an embedding process in a non-magnetic material and a magnetic recording layer surface shaping process are performed.
The nonmagnetic material 21 to be embedded may be any material that is nonmagnetic and does not degrade the soft magnetic layer 23 that is in contact therewith. For example, SiO ₂ or SiN ₂ may be embedded by sputtering, CVD, vapor deposition, or the like. In order to flatten the surface of the magnetic recording layer 5 after embedding, it is preferable to perform a magnetic recording layer surface shaping step such as polishing and etching. After these steps, the magnetic layer 5 as shown in FIG.

  In order to finally make a recording medium, the protective layer 6 and the lubricating layer 7 may be formed on the magnetic recording layer 5 formed as described above using a normal film formation process.

Example 2
In this embodiment, the central portion of the substantially cylindrical magnetic region embedded in the nonmagnetic material is configured as a soft magnetic layer made of a soft magnetic material, and the outer peripheral portion is formed as a hard magnetic layer made of a hard magnetic material. Is provided with a nonmagnetic layer.

  FIG. 10 shows the configuration of the magnetic recording layer 5 in this embodiment. In FIG. 10, 5 denotes a magnetic recording layer as in FIG. As in FIG. 2, 22 is a magnetic region, 21 is a nonmagnetic material that magnetically separates each magnetic region 22, and 23 is a soft magnetic layer that constitutes the magnetic region 22. Reference numeral 23 denotes a nonmagnetic layer constituting the magnetic region 22, and reference numeral 25 denotes a hard magnetic layer constituting the magnetic region 22. In contrast to the first embodiment, the magnetic region 22 according to the present embodiment is characterized by a soft magnetic layer 23 made of a soft magnetic material on the inner side in the radial direction of the cylindrical magnetic region 22 and a hard magnetic material made of a hard magnetic material on the outer side. A magnetic layer 25 is provided, and a nonmagnetic layer 24 is provided between both magnetic layers. Similarly to the first embodiment, the soft magnetic layer and the hard magnetic layer may have a multilayer structure of two or more layers, and a nonmagnetic layer may be provided between them.

  FIG. 11 shows a state of a demagnetizing field in the vicinity of the magnetic region 22 on the magnetic recording layer 5 and a state of magnetization reversal in the magnetic region when a recording magnetic field is applied. FIG. 11A schematically shows the magnetization direction in the magnetic region 22 and the demagnetizing field in the vicinity thereof when no recording magnetization is applied. FIGS. 11B to 11D schematically show the reversal of the magnetization direction in the magnetic region 22 before and after the recording magnetic field is applied. The reference numerals in the figure are the same as those in FIGS.

  In FIG. 11A, in this embodiment, the magnetization directions of the soft magnetic layer 23 near the center of the magnetic region 22 and the hard magnetic layer 25 around the magnetic region 22 are antiparallel, and the magnetic lines of force are closed magnetic circuit as in FIG. Is effective in suppressing the generation of a demagnetizing field in the periphery.

  FIG. 11B schematically shows the magnetization direction in the magnetic region 22 before applying the recording magnetic field, FIG. 11C when the recording magnetic field is applied, and FIG. Due to the recording magnetic field Hext applied from the recording magnetic head, the magnetization directions of both the soft magnetic layer 23 and the hard magnetic layer 25 are parallel to each other in the direction of the recording magnetic field Hext in FIG. In FIG. 11D in which the recording magnetic field disappears, the hard magnetic layer 25 having a large magnetic anisotropy energy density maintains the magnetization direction. The soft magnetic layer 23 having a small magnetic anisotropy energy density reverses the magnetization direction by the demagnetizing field from the hard magnetic layer 25, and the magnetization directions of the hard magnetic layer 25 and the soft magnetic layer 23 are antiparallel and stabilized. .

  Unlike the first embodiment, a soft magnetic layer 23 that reverses the magnetization direction after applying the recording magnetic field Hext exists in the central portion of the magnetic region 22. As in the first embodiment, it is possible to record information on the magnetic recording medium with the magnetization direction of the hard magnetic layer 25 as the signal recording direction. In this case, since the hard magnetic layer 25 for generating a signal to be reproduced exists around the magnetic region 22, the reproduction signal waveform of the isolated pit becomes broad, which is not preferable from the viewpoint of reproduction resolution.

  From this point, in this embodiment, it is also possible to adopt an anti-phase recording method in which the directions of the magnetic fields at the time of the reproduction signal and the recording signal are reversed. Specifically, the magnetization direction corresponding to the signal to be recorded may be assigned to the magnetization direction of the soft magnetic layer 23 existing at the center of the magnetic region 22. Therefore, the product of the cross-sectional area of the hard magnetic layer 25 on the surface of the magnetic recording layer 5 and the magnitude of the saturation magnetization Ms is the product of the cross-sectional area of the soft magnetic layer 23 on the surface of the magnetic recording layer 5 and the magnitude of the saturation magnetization Ms. Try to be less than half. As a result, the direction of the magnetic field detected when the reproducing head is on the central portion of the magnetic region 22 is the magnetization direction of the soft magnetic layer 23 existing at the center of the magnetic region 22. This direction is opposite to the direction of the applied recording magnetic field as shown in FIG.

  As shown in FIG. 11, the direction of the applied recording magnetic field is recorded in the magnetization direction of the hard magnetic layer 25. After the application, the soft magnetic layer 23 is demagnetized by the demagnetizing field from the hard magnetic layer 25 as shown in FIG. Is always in an antiparallel direction to the magnetization direction of the hard magnetic layer 25. For this reason, the direction of the reproducing magnetic field from the magnetic region 22 at the time of reproduction is opposite to the direction of the applied magnetic field at the time of recording. In other words, the recording signal can correspond to the reproduction signal by recording or reproducing the reproduction signal and the recording signal in the opposite phase with the phase changed by 180 degrees.

  In the present embodiment, the demagnetizing field suppressing effect and the reproduction signal intensity are increased by increasing the thickness and saturation magnetization Ms of the soft magnetic layer 23. However, if the volume of the soft magnetic layer 23 is decreased, the soft magnetic layer 23 is easily affected by thermal fluctuations. It becomes difficult to hold the direction. However, by using the L10 ordered alloy FePt, FePd, CoPt, or CoPd for the soft magnetic layer 23, a magnetic anisotropy energy density that is about one digit larger than that of a conventional hard magnetic material can be obtained. Therefore, preferably, the product of the cross-sectional area of the soft magnetic layer 23 on the surface of the magnetic recording layer 5 and the magnitude of the saturation magnetization Ms, and the cross-sectional area of the hard magnetic layer 25 on the surface of the magnetic recording layer 5 and the magnitude of the saturation magnetization Ms. The product ratio can be about 10: 1 to 2: 1.

  The recording signal of this embodiment needs to take the conventional recording signal in the opposite phase, and the signal processing circuit of the conventional HDD recording apparatus needs to be slightly changed, but the main change is the inversion of the signal phase. Compared to the device described in Patent Document 3 of the prior art, this can be realized more easily.

  In order to create the magnetic recording layer 5 according to the present embodiment, a substantially cylindrical magnetic layer is formed by combining a magnetic material into a large number of holes in the porous member in substantially the same manner as in the first embodiment. Thereafter, the base material of the porous member is removed, a nonmagnetic layer and a magnetic layer are formed outside the magnetism, and the space between the layers is filled with a nonmagnetic material to create the embodiment shown in FIG. The difference from the first embodiment is that a magnetic material which is firstly fitted into the pores of the porous member is a soft magnetic material, and a magnetic material which is coated on the nonmagnetic layer is a hard magnetic material. The combination and coating of each magnetic layer and non-magnetic layer may be made by electrolytic plating in the same manner as in the first embodiment, and can be created in substantially the same process as in the first embodiment by replacing the electrolytic plating procedure. Details are omitted.

  The outline will be described below. First, a porous member constituting the nonmagnetic underlayer 4 and the magnetic recording layer 5 later is formed on the soft magnetic backing layer 3. Next, the soft magnetic material constituting the soft magnetic layer 23 is combined in the pores of the porous member. Next, a part of the base material portion of the porous member is removed to expose the soft magnetic material portion. Next, a nonmagnetic material constituting the nonmagnetic layer 24 is laminated on the exposed soft magnetic material portion. Further, a hard magnetic material constituting the hard magnetic layer 25 is laminated on the nonmagnetic material. Further, a hard magnetic material portion wrapped with a soft magnetic material constituting the magnetic region is embedded with a nonmagnetic material. Finally, the surface portion is shaped to form the magnetic recording layer 5.

  The soft magnetic material can be combined by electrolytic plating using the nonmagnetic underlayer 4 as an electrode. The nonmagnetic underlayer 4 is obtained by forming a conductive film such as Pt for use as an electrode as in the first embodiment. For example, a plating solution in which boric acid as a buffer, sodium saccharin as an additive, sodium laurate as a surfactant, etc. is added to a mixed solution of nickel sulfate, nickel chloride and iron sulfate. Then, electrolytic plating may be performed to fit the soft magnetic layer 23 made of permalloy into the hole.

  Thereafter, a part of the porous base material is removed with an alkaline solution or the like, and the exposed soft magnetic layer 23 is used as an electrode from Pt or Pd using a plating solution containing hexachloroplatinum (IV) or hexachloroPd. The nonmagnetic layer 24 is coated. Thereafter, using the plating solution described in Example 1, either FePt or FePd, CoPt, or CoPd is plated. After plating, heat treatment is performed in a hydrogen atmosphere at 400 to 650 degrees to form a hard magnetic layer 25 of an L10 ordered alloy.

Finally, the magnetic recording layer 5 may be formed by sputtering SiO ₂ or the like and filling the protrusions.

Example 3
In this embodiment, the present invention is applied to a magnetic recording medium described in Patent Document 3 in the prior art.

  FIG. 12 shows the configuration of the magnetic recording layer in this example. The reference numerals are the same as in FIG. 2, 21 is a nonmagnetic material, 22 is a magnetic region, 23 is a soft magnetic layer constituting the magnetic region, 24 is a nonmagnetic layer constituting the magnetic region, and 25 is a magnetic region. It is the hard magnetic layer which comprises.

  In this embodiment, the cross section of the magnetic region 22 in the plane of the magnetic recording layer 5 has a substantially square shape, and the nonmagnetic layer 24 and the soft magnetic layer 23 surround the hard magnetic layer 25 and do not form a continuous layer. The hard magnetic layer 25 is disposed before and after the hard magnetic layer 25 in the recording track direction.

Also in this configuration, as shown in FIG. 5, the magnetization of the hard magnetic layer 25 and the soft magnetic layer 23 are antiparallel, so that the effect of canceling the demagnetizing field with respect to the recording track direction is produced.
In this embodiment, a hard magnetic material having a high magnetic anisotropy energy density is formed on the nonmagnetic underlayer. Next, a pattern of the hard magnetic layer 25 is first created by an electron drawing method, an optical interference lithography method, an X-ray lithography method, a scanning probe microscope method, an ion beam lithography method, or the like. In particular, the pattern of the hard magnetic layer 25 is preferably formed by reactive ion etching using a mixed gas of carbon monoxide and ammonia. The hard magnetic layer material can be made of L1 ordered FePt, FePd, CoPt, CoPd alloy, or a conventionally used magnetic material such as CoCrPt, CoCrTa, etc. You may form into a film by the film-forming method.

After creating the pattern of the hard magnetic layer 25, the nonmagnetic layer 24 and the soft magnetic layer 23 are formed on the side surfaces of the hard magnetic layer 25 pattern by oblique vapor deposition. The material of the nonmagnetic layer 24 may be Pt, Pd, or the like, but a cheaper oxide such as SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , or nitride may be used. The soft magnetic layer 25 may be made of a soft magnetic material having a large saturation magnetization Ms and a low magnetic anisotropy energy density as long as it can be deposited and sputtered. Can be used.

Finally, the magnetic region 22 may be embedded in a nonmagnetic material such as SiO ₂ , Si ₃ N ₄ , Al ₂ O _3, and the surface may be polished and etched.
Since the patterning process is used in this embodiment, the selection range of the materials used for the hard magnetic layer 23, the nonmagnetic layer 24, and the soft magnetic layer 25 is wider than those of the first and second embodiments using mainly the plating method. I can take it. In particular, the nonmagnetic layer 24 has an advantage that an inexpensive material other than Pt and Pd as in the first and second embodiments can be selected.

  In this embodiment, the nonmagnetic layer 24 and the soft magnetic layer 23 do not form a continuous layer surrounding the hard magnetic layer 25, and are arranged before and after the hard magnetic layer 25 in the recording track direction across the hard magnetic layer 25. I explained what was arranged. In addition, for those having a wide interval between the magnetic regions 22, the nonmagnetic layer 24 and the soft magnetic layer 23 can surround the hard magnetic layer 25 by performing oblique vapor deposition in the direction perpendicular to the recording track. .

  Further, since the present embodiment mainly cancels the demagnetizing field in the recording track direction, it has a drawback that the demagnetizing field hardly cancels in the direction perpendicular to the recording track. However, since the track direction is generally the head running direction, the recording density is high, and in the track vertical direction, the recording density cannot be increased as much as the track direction due to the influence of the head tracking control. For this reason, since the width between the magnetic regions 22 is generally wider in the track vertical direction than in the track direction, this configuration also has an effect of easily reducing recording noise.

  In particular, it is possible to reduce variations in recording sensitivity between the magnetic recording layers 5 due to the demagnetizing field in the track vertical direction by providing the surface of the magnetic recording layer 5 with irregularities in the track direction.

  The magnetic recording medium according to the present invention can be used in high-density magnetic recording devices such as HDD devices, information processing devices including these devices, image recording devices, and the like.

1 is a diagram illustrating a configuration of a perpendicular recording medium according to the present invention. It is a figure which shows the structure of the magnetic-recording layer of 1st embodiment in connection with this invention. It is a figure for demonstrating the creation method of the magnetic-recording layer of the perpendicular recording medium concerning this invention. It is a figure which shows the structure of the perpendicular | vertical recording medium in a prior art example. It is a figure showing the mode of the magnetic field near magnetic field in a first embodiment of the present invention. It is a schematic diagram showing the direction of the magnetization in the magnetic area | region in 1st embodiment of this invention. It is a figure for demonstrating the effect of the nonmagnetic layer in this invention. It is a figure which shows the structure of the magnetic-recording apparatus using the perpendicular recording medium concerning this invention. It is a figure which shows the porous member in the preparation methods of the magnetic-recording layer concerning this invention. It is a figure which shows the structure of the magnetic-recording layer of 2nd embodiment in connection with this invention. It is a schematic diagram showing the direction of the magnetization in the magnetic area | region in 2nd embodiment of this invention. It is a figure which shows the structure of the magnetic-recording layer of 2nd embodiment in connection with this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Underlayer 3 Soft magnetic backing layer 4 Nonmagnetic underlayer 5 Magnetic recording layer 6 Protective layer 7 Lubricating layer 8 Parallel to the film surface of the magnetic recording layer 21 Nonmagnetic material 22 Magnetic region 23 Soft magnetic layer 24 Non Magnetic layer 25 Hard magnetic layer 26 Magnetic flux line 300 Porous member 301 Hole 302 Base material 303 Encapsulated material 304 Protruding structure (hard magnetic material)
305 Base material remainder 306 Protruding structure (non-magnetic material coating)
307 Protruding structure (coated with soft magnetic material)
401 Soft magnetic backing layer 402 Nonmagnetic underlayer 403 Perpendicular magnetic recording layer 404 Magnetic region 405 Nonmagnetic region 406 Magnetic domain 407 Magnetic head for recording

Claims (11)

  In a magnetic recording medium having a magnetic recording film in which a plurality of magnetic regions are independently provided in a base material made of a non-magnetic material, the magnetic region has at least a soft magnetic layer and a hard layer in the in-plane direction of the magnetic recording film. A magnetic recording medium comprising at least one magnetic layer and a nonmagnetic layer made of a nonmagnetic material between the soft magnetic layer and the hard magnetic layer.   2. The magnetic region according to claim 1, wherein a nonmagnetic layer is provided surrounding the hard magnetic layer around the hard magnetic layer, and a soft magnetic layer is provided surrounding the nonmagnetic layer. Magnetic recording medium.   2. The magnetic region according to claim 1, wherein a nonmagnetic layer is provided surrounding the soft magnetic layer around the soft magnetic layer, and a hard magnetic layer is provided surrounding the nonmagnetic layer. Magnetic recording medium.   2. The magnetic region according to claim 1, wherein a nonmagnetic layer is provided with the hard magnetic layer sandwiched around the hard magnetic layer, and a soft magnetic layer is provided with the nonmagnetic layer sandwiched therebetween. Magnetic recording medium.   2. The magnetic region according to claim 1, wherein a nonmagnetic layer is provided with the soft magnetic layer sandwiched around the soft magnetic layer, and a hard magnetic layer is provided with the nonmagnetic layer sandwiched therebetween. Magnetic recording medium.   6. The magnetic recording medium according to claim 1, wherein an average magnetic anisotropy energy density of the soft magnetic layer is smaller than an average magnetic anisotropy energy density of the hard magnetic layer.   7. The magnetic recording medium according to claim 1, wherein the magnetization directions of the soft magnetic layer and the hard magnetic layer are antiparallel when no external recording magnetic field is applied.   7. The magnetization direction of the soft magnetic layer and the hard magnetic layer is parallel to the direction of the applied magnetic field when an external recording magnetic field is applied. Magnetic recording medium.   9. The magnetic recording medium according to claim 7, wherein the magnetization direction of the soft magnetic layer is antiparallel to the magnetization direction of the hard magnetic layer after an external recording magnetic field is applied.   The product of the cross-sectional area of the soft magnetic layer on the magnetic recording film surface and the magnitude of the saturation magnetization is smaller than the product of the cross-sectional area on the magnetic recording film surface of the hard magnetic layer and the magnitude of the saturation magnetization. The magnetic recording medium according to claim 1.   The product of the cross-sectional area of the hard magnetic layer on the magnetic recording film surface and the magnitude of the saturation magnetization is smaller than the product of the cross-sectional area on the magnetic recording film surface of the soft magnetic layer and the magnitude of the saturation magnetization. The magnetic recording medium according to claim 1.

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