JP2008176846A - Substrate for magnetic recording medium, manufacturing method, and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate suitable for manufacturing vertical magnetic recording medium which has good signal reproducing characteristic with low noise and a manufacturing method thereof. <P>SOLUTION: On the non magnetic substrate 1, preferably a core forming layer 2 is formed, and a multilayer soft magnetic backing layer 3 including antiferromagnetic film is formed on the layer 2. The soft magnetic backing layer 3 is exchange coupled between the soft magnetic film and the antiferromagnetic film, and has anisotropy in the circumferential direction or radial direction. The antiferromagnetic film is an alloy film preferably including Cr or Mn or metal oxide film except natural oxidization, and is obtained by film forming like plating. Anisotropic processing is carried out by thermal treatment in a magnetic field, and circumferential or radial anisotropy is made by changing the direction of applying the magnetic field, and a magnetic recording layer 5 for vertical magnetic recording is formed on the soft magnetic backing layer 3. Further, a protection layer 6 and a lubricating layer 7 are favorably laminated in order. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium substrate, a manufacturing method thereof, and a magnetic recording medium, and more particularly to a substrate suitable for manufacturing a perpendicular magnetic recording medium having low noise and good signal reproduction characteristics, and a manufacturing method thereof.

  In the technical field of information recording, hard disk devices (hereinafter referred to as HDDs), which are means for magnetically reading and writing information such as characters, images, and music, are primary external recording devices and built-in type electronic devices such as personal computers. It is indispensable as a recording means. Such HDDs have a built-in hard disk as a magnetic recording medium. Conventional hard disks employ a so-called “in-plane magnetic recording method (horizontal magnetic recording method)” in which magnetic information is written horizontally on the disk surface. It was.

  FIG. 9 is a schematic cross-sectional view for explaining a general laminated structure of a horizontal magnetic recording type hard disk. A Cr-based underlayer 103 and a magnetic recording layer 105 are formed on a nonmagnetic substrate 101 by sputtering. And the carbon layer as the protective film 106 is laminated | stacked one by one, and the lubrication layer 107 formed by apply | coating a liquid lubricant on the surface of this carbon layer is formed (for example, refer patent document 1). The magnetic recording layer 105 is a uniaxial crystal magnetic anisotropy Co-based alloy such as CoNiCr, CoCrTa, or CoCrPt, and the alloy film is magnetized horizontally to the disk surface to record information.

  However, in such a horizontal magnetic recording system, if the size of each crystal grain is reduced in order to increase the recording density, the N poles and S poles of adjacent recording bits repel each other and magnetization cancels out. . In order to increase the recording density, it is necessary to reduce the thickness of the magnetic recording layer to reduce the vertical size of the crystal grains, and as the crystal grains become finer (smaller volume), the thermal energy Problems such as the occurrence of the phenomenon of “thermal fluctuation” in which the magnetization direction of crystal grains is disturbed and data is lost have been pointed out, and there is a limit to increasing the recording density.

In view of such problems, the “perpendicular magnetic recording method” has been studied. In this recording method, since the magnetic recording layer is magnetized perpendicularly to the disk surface, the N bits and S poles of the recording bits are alternately bundled and arranged in bits, and the N and S poles of each recording bit are adjacent to each other. In other words, the demagnetizing field is lowered. As a result, the stability of the magnetization state (magnetic recording) is increased. Unlike the horizontal magnetic recording method, it is not necessary to reduce the thickness of the crystal grains in the vertical direction. For this reason, even if the horizontal size of the crystal grains is reduced, if the recording layer thickness is increased and the vertical direction is increased, the entire recording volume increases and the influence of “thermal fluctuation” is reduced. It is possible.
That is, the perpendicular magnetic recording method can reduce the demagnetizing field and ensure the K _u V value (K _u is the magnetocrystalline anisotropy energy of the magnetic recording layer and V is the unit recording bit volume). This is a magnetic recording system that reduces the instability of magnetization and greatly expands the limit of recording density, and is therefore expected as a system for realizing ultra-high density recording.

FIG. 10 is a schematic cross-sectional view for explaining the basic layer structure of a hard disk as a “perpendicular dual-layer magnetic recording medium” in which a recording layer for perpendicular magnetic recording is provided on a soft magnetic underlayer (SUL). FIG. On the nonmagnetic substrate 111, a soft magnetic backing layer 113, a magnetic recording layer 115, a protective layer 116, and a lubricating layer 117 are sequentially laminated. Here, permalloy, CoZrTa amorphous, or the like is typically used for the soft magnetic backing layer 113. As the magnetic recording layer 115, a CoCrPt-based alloy film, a PtCo film, a multilayer film in which several ultrathin films of Pd and Co are laminated, an FePt film , an SmCo amorphous film, or the like is used.

  As shown in FIG. 10, a perpendicular magnetic recording type hard disk normally includes a magnetic recording layer 115, a protective layer 116, and a lubricating layer 117 on a substrate 111. A soft magnetic backing layer 113 is provided as an underlayer for the magnetic recording layer 115. Its magnetic property is “soft magnetic”, and the layer thickness is about 100 to 500 nm. This soft magnetic backing layer 113 is for increasing the write magnetic field and reducing the demagnetizing field of the magnetic recording film. The soft magnetic underlayer 113 is a path for the magnetic flux from the magnetic recording layer 115 and a path for the write magnetic flux from the recording head. Function as. That is, the soft magnetic backing layer 113 plays the same role as the iron yoke in the permanent magnet magnetic circuit. For this reason, it is necessary to set the layer thickness thicker than the layer thickness of the magnetic recording layer 115 for the purpose of avoiding magnetic saturation at the time of writing.

From the viewpoint of the laminated structure, the soft magnetic backing layer 113 corresponds to the Cr-based underlayer 103 provided in a horizontal magnetic recording type hard disk, but the film formation is performed on the Cr-based underlayer 103 of the horizontal recording medium. It is not easy compared with film formation.
The thickness of each layer of the hard disk in the horizontal magnetic recording system is at most about 20 nm, and all are formed by a dry process (mainly magnetron sputtering) (see Patent Document 1).

  Various methods for forming the magnetic recording layer 115 and the soft magnetic backing layer 113 by a dry process have also been studied in the perpendicular double-layer recording medium. When the soft magnetic backing layer 113 is formed by a dry process, sputtering is performed. The film thickness uniformity, composition uniformity, target because the target is a ferromagnetic material with a large saturation magnetization and the thickness of the soft magnetic underlayer 113 is required to be 100 nm or more. Lifetime, process stability, and above all, low film deposition speeds have major problems in terms of mass productivity and productivity.

  In order to increase the recording density, it is necessary to reduce the flying height of the magnetic head that floats on the magnetic disk surface as much as possible. The smoothness tends to deteriorate, and this may cause a head crash.

For these reasons, attempts have been made to form the soft magnetic backing layer 113 by a plating method that is easy to thicken and that can be polished (see, for example, Patent Document 2).
JP-A-5-143972 JP 2005-108407 A

When a soft magnetic layer is formed by plating, a large number of magnetic domains are generated in a specific direction over a range of several mm to several cm on the surface of the plating film constituting the soft magnetic layer. A domain wall is generated. In particular, the domain wall is remarkable when the soft magnetic layer has anisotropy in the radial direction. When a soft magnetic film having such a domain wall is used as a backing layer for a hard disk for a perpendicular double-layer magnetic recording medium, an isolated pulse noise called spike noise or micro spike noise is generated due to a leakage magnetic field generated from the domain wall portion, There is a possibility that the signal reproduction characteristic is greatly impaired. The spike noise is mainly caused by the domain wall of the soft magnetic film, and can be suppressed to some extent by imparting anisotropy to the film.
However, the generation of spike noise is not completely suppressed even in the anisotropic soft magnetic film, and spike noise is particularly remarkable in the case of a soft magnetic film having radial anisotropy. In addition to anisotropy of the soft magnetic film, it is required to suppress spike noise.

  In order to obtain a perpendicular double-layer magnetic recording medium having excellent characteristics by a simple method, the present inventors have intensively studied the conditions for forming a soft magnetic underlayer by plating and the types of applicable soft magnetic films. Repeated. As a result, it is possible to suppress the occurrence of domain walls by laminating a soft magnetic film and an antiferromagnetic film in an appropriate combination using a plating method or the like on a non-magnetic substrate and exchange coupling them. I found it. This effect is effective for both soft magnetic films having anisotropy in the in-plane circumferential direction or in-plane inner diameter direction of the substrate, but is particularly effective in the case of radial anisotropy. The reason is that the radial anisotropic soft magnetic film has a Bloch type domain wall at a thickness of several hundred nm, while the circumferential anisotropic soft magnetic film has a nail type up to several hundred nm. Therefore, the spike noise of the radial direction anisotropic film is considerably large. Since the generation of the Bloch domain wall can be suppressed by the multilayer structure, it is considered that the radial anisotropy is more effective.

Here, “anisotropy” means the difference (δH = H _d −H _c ) between the magnetization saturation magnetic field strength (Hd) in the in-plane inner diameter direction and the magnetization saturation magnetic field strength (H _c ) in the in-plane circumferential direction. When δH is positive (H _d −H _c > 0), the surface inner diameter direction is the easy magnetization direction, and when δH is negative (H _d −H _c <0), the in-plane circumferential direction is magnetization. It means easy direction.

  That is, according to the present invention, a multilayer soft magnetic layer including an antiferromagnetic film is laminated by a plating method or the like, and subjected to an anisotropy treatment, so that a perpendicular two-layer magnetic recording medium having a good S / N ratio with less spike noise. An object of the present invention is to provide a substrate suitable for the manufacture of the substrate and a method for manufacturing the substrate.

The present invention is a substrate for a magnetic recording medium having a soft magnetic backing layer on a disc-shaped nonmagnetic substrate having a diameter of 90 mm or less and having a center hole, and the soft magnetic backing layer does not matter in any order. Provided is a substrate for a magnetic recording medium comprising at least one soft magnetic film formed by using a plating method and at least one antiferromagnetic film and having circumferential or radial magnetic anisotropy. The antiferromagnetic film is preferably a film of an alloy containing Cr or Mn or a metal oxide film other than natural oxidation, and is exchange-coupled to the soft magnetic film, has a Neel temperature of 100 ° C. or more, and has a film thickness. It is 5 nm or more and 50 nm or less. The metal oxide film is preferably a film obtained by surface-oxidizing at least one of the soft magnetic films.
The present invention also provides a method for manufacturing a substrate for a magnetic recording medium having a soft magnetic backing layer on a disk-shaped nonmagnetic substrate having a diameter of 90 mm or less and having a central hole, whichever is performed first. A step of forming a soft magnetic film using a plating method, a step of forming a soft magnetic backing layer including at least one step of forming an antiferromagnetic film, and a circumference or a diameter of the soft magnetic backing layer. Provided is a method for manufacturing a magnetic recording medium substrate, which includes a step of imparting directional magnetic anisotropy. At least one of the steps of forming the diamagnetic film is preferably performed using a plating method.
In addition, at least one of the steps of forming the antiferromagnetic film preferably includes oxidizing the surface of the soft magnetic film formed by using a plating method, and more preferably, the surface of the soft magnetic film. Oxidation is performed in an oxidizing agent solution or in an oxidizing atmosphere.
Furthermore, the present invention provides a perpendicular recording medium using this magnetic recording medium substrate.

In a particularly preferred embodiment, the soft magnetic backing layer provided on the magnetic recording medium substrate of the present invention has at least two elements selected from the group consisting of Co, Ni and Fe, B, C, P and S. A soft magnetic plating film made of an alloy containing at least one element selected from the group consisting of: an antiferromagnetic plating film having a Neel point of 100 ° C. or higher, and the direction of easy magnetization of the soft magnetic underlayer Is subjected to heat treatment in a magnetic field after plating so as to be in the direction of the inner diameter of the surface or in the direction of the inner surface of the surface, so that the domain wall generation is suppressed and spike noise is reduced.
For this reason, a hard disk in which a magnetic film for perpendicular magnetic recording is provided on the soft magnetic underlayer can provide a high recording density magnetic recording medium having good writing characteristics due to an increase in head magnetic flux. In addition, the magnetic recording medium substrate of the present invention greatly simplifies the manufacturing process compared to dry process film formation such as vapor deposition, especially when the soft magnetic underlayer is formed by a wet plating method. It is also excellent in productivity.

EMBODIMENT OF THE INVENTION Below, the form for implementing this invention with reference to drawings is demonstrated in detail.
The magnetic recording medium substrate of the present invention is for perpendicular magnetic recording. By forming a magnetic recording layer on a soft magnetic underlayer, a hard disk as a perpendicular double-layer magnetic recording medium can be obtained. That is, the magnetic recording medium substrate of the present invention is provided with a soft magnetic backing layer 3 formed on a nonmagnetic substrate 1 by plating or the like, as shown in FIG. Then, for example, an orientation control intermediate film 4 is preferably formed on the soft magnetic underlayer 3, a perpendicular magnetic recording magnetic recording layer 5 is formed, and a protective layer 6 and a lubricating layer 7 are preferably formed. By sequentially laminating, the magnetic recording medium of the present invention can be obtained.

  When using the soft magnetic backing film substrate of the present invention, as shown in FIG. 1, a nucleation film (undercoat layer) is preferably provided between the single crystal Si substrate preferable as the nonmagnetic substrate 1 and the soft magnetic backing layer 3. 2 is provided. The soft magnetic backing layer 3 is composed of two or more layers including a soft magnetic film and an antiferromagnetic film.

  The non-magnetic substrate used for the magnetic recording medium substrate of the present invention is preferably a single crystal Si substrate. When a single crystal Si substrate is used as the nonmagnetic substrate, there is an advantage that the atomic arrangement on the surface is uniform in the plane, and the surface chemical state and the surface potential state in the plating process are also uniform in the plane. In addition, when a nucleation film of Ni or NiP is formed, direct plating on a single crystal Si substrate is possible, and magnetic non-uniformity due to non-uniform plating can be suppressed.

As the single crystal Si substrate, a crystal grown by the CZ (chocolate ski) method or the FZ (floating zone) method is easily available. There is no particular limitation on the plane orientation of the substrate, and any plane orientation such as (100), (110), or (111) may be used. Further, as an impurity contained in the substrate, a donor or acceptor up to about 10% (−10 ²² atoms / cm ³ ) by atomic ratio with Si or a light element such as oxygen, carbon, or nitrogen may be included.

  In the present invention, the nonmagnetic substrate has a substrate diameter of 90 mm or less and a center hole. This is because the purpose is to produce an HDD small-diameter substrate for high recording density.

When a single crystal Si substrate is used as the nonmagnetic substrate, a nucleation film is preferably provided between the single crystal Si substrate and the soft magnetic backing layer. The nucleation film is effective for ensuring mutual adhesion between the soft magnetic backing layer and the single crystal Si substrate.
As the nucleation film, Ni, NiP, NiFe or the like is used, and preferably has plating activity when the upper soft magnetic underlayer is plated. Ni can be formed by displacement plating, and NiP and NiFe can be plated by adding a reducing agent. The details of the former two are described in the already filed patent (Patent Document 2). In the case of NiFe, a plating bath (for example, nickel sulfate and iron sulfate) is used as a predetermined liquid composition, and the other steps may be performed in the same manner as in the case of NiP.
The thickness of the nucleation film is preferably 10 to 1000 nm.

  A nonmagnetic layer (Cu or Pd) may be further formed between the nucleation film and the soft magnetic backing layer.

  The soft magnetic underlayer of the present invention has a multilayer structure including at least one soft magnetic film and at least one antiferromagnetic film. By giving exchange coupling to the soft magnetic film with the antiferromagnetic film, the generation of the domain wall is suppressed by the influence of the applied exchange magnetic field. The exchange coupling between the antiferromagnetic film and the soft magnetic film is a particle exchange coupling at the interface between the soft magnetic material and the diamagnetic material, and is a coupling that suppresses noise on the domain wall.

  It has also been proposed to use an antiferromagnetic layer in the formation of a soft magnetic underlayer by sputtering (Japanese Patent Laid-Open Nos. 2002-279615 and 2002-342909). In terms of the configuration of the soft magnetic backing layer, it does not differ greatly from the sputtered film. However, the present inventors have found that the multilayer soft magnetic underlayer mainly formed by plating in the present invention has advantages not found in the film formed by sputtering.

  The magnetic properties (exchange coupling state) of the multilayer soft magnetic backing film by sputtering are very sensitively influenced by the ferromagnetic film thickness and the antiferromagnetic / ferromagnetic interface. In a ferromagnetic film formed by sputtering, as the film thickness increases, the magnetization of the film always tends to have a perpendicular component. Since the perpendicular component of the soft magnetic backing film becomes noise, it is not preferable. That is, since the magnetization tends to rise from the in-plane, it is necessary to strongly pin the antiferromagnetic film and tilt it in the plane. A ferromagnetic film thickness control capable of pinning and a smooth and good interface with little element diffusion are required, and it is said that the film thickness capable of pinning is up to about 100 nm. Therefore, it is required to precisely control each multilayer film.

  On the other hand, the multilayer soft magnetic underlayer mainly formed by plating of the present invention can be pinned even if the ferromagnetic film is thick and can exert exchange coupling up to about 1000 nm. This is because the residual stress acts strongly on the plated ferromagnetic film and the magnetization is strongly bound in the plane, so that it is not necessary to suppress the perpendicular component of the magnetization. For this reason, it has been found for the first time that the ferromagnetic film thickness can be adjusted to the required film thickness up to 1000 nm, and that there is no problem in pinning even if the ferromagnetic film is several hundred nm thick. Furthermore, since plating is performed at a low temperature, element interdiffusion between layers at the antiferromagnetic / ferromagnetic interface does not occur. The smoothness of the interface is not as smooth as the sputtered film. The reason for this is not clear, but it is thought that this is because the interface atomic layer is not damaged because of low-temperature film formation. In the multilayer soft magnetic backing layer by plating of the present invention, it has not been known that such an effect (in other words, it is not sensitive to the structure and film thickness) has been conventionally known. This is a great advantage compared to the layer.

Examples of the structure of the multilayer soft magnetic backing layer according to the present invention are shown in FIGS. 2A to 2E, but the present invention is not limited to this. In FIGS. 2A to 2E, the antiferromagnetic film (AFL) is only one layer, but a plurality of films may be used as necessary.
FIG. 2A shows an embodiment in which a nucleation film 2F, a soft magnetic film 3S, an antiferromagnetic film 3A, and a soft magnetic film 3S are sequentially provided on the substrate 1. FIG. 2B shows a ferromagnetic nucleation film. 2F, an antiferromagnetic film 3A, and a soft magnetic film 3S are sequentially provided. FIG. 2C is an exemplary embodiment in which a soft magnetic nucleation film 2S, an antiferromagnetic film 3A, and a soft magnetic film 3S are sequentially provided. ) Shows an embodiment in which a nonmagnetic nucleation film 2N, an antiferromagnetic film 3A, and a soft magnetic film 3S are sequentially provided. FIG. 2E shows a nonmagnetic nucleation film 2N, a soft magnetic film 3S, and an antiferromagnetic film 3A. The mode of providing sequentially is shown.

  In FIG. 2D, a nucleation film having soft magnetism (for example, NiFe or the like) is used, and the layer functions as both nucleation and a soft magnetic layer.

  The soft magnetic film is usually formed by electroless plating. As the plating bath, either a sulfide bath or a chloride bath can be used, and various metal species can be employed as the metal species contained in the bath. Preferably, a metal containing at least two elements selected from the group consisting of Co, Ni, and Fe because it is necessary to make the magnetic properties of the plating film as a soft magnetic film and at the same time make the crystal structure cubic. A salt-containing plating bath is selected. The reason for selecting such a metal element is that although Co, Ni, and Fe can be electrolessly plated, it is difficult to obtain good soft magnetic properties from a single element plating film. is there. Specific examples of the bath composition include a nickel sulfate and cobalt sulfate mixed bath, or a mixed bath containing iron sulfate, and the preferred concentration is 0.01 to 0.5N. In addition, it is preferable to set the temperature of a plating bath in the range of 40-95 degreeC.

In addition, in such a plating bath, at least one element selected from the group consisting of B, C, P, and S is significantly (preferably 3 at% (atomic%) or less) contained in the plating film. Thus, if necessary, a reducing agent corresponding to the metal ions contained in the bath is added. Examples of such a reducing agent include hypophosphorous acid (H ₂ PO ₂ ) and dimethylamine borane (DMAB: (CH ₃ ) ₂ HNBH ₃ ). The inclusion of at least one element of B, C, P, and S in the plated film is in consideration of the soft magnetic properties of the film, and at least one of these elements is significant. The point of inclusion in is a significant difference from a dry film forming method such as a sputtering method.

Of the multilayer magnetic backing layer, at least one antiferromagnetic film is provided. The antiferromagnetic film is preferably composed of a metal antiferromagnetic film such as an alloy film or a metal oxide film other than natural oxidation.
Examples of the antiferromagnetic film of the alloy include a Cr-based alloy (Cr—Mn, Cr—Pt, Cr—Ru, Cr—Rh, Cr—Ir, Cr—Os, Cr—Re, etc.) and a Mn alloy (Mn—Pt). , Mn-Ir, etc.) may be used, and a mixed system thereof may be used. In view of ease of plating, a Cr alloy is particularly desirable.
Cr alone has an antiferromagnetic Neel temperature (a temperature at which an antiferromagnetic structure changes to a paramagnetic structure), which is as low as about 310 K. However, transition metals such as Mn, noble metals such as Pt, Ru, Rh, Ir, Os, Re, etc. By adding about 1 to 10 at%, preferably 1 to 5 at%, the temperature can be raised by 100 K or more, and the Neel temperature can be made 100 ° C. or more. The multilayer magnetic backing layer 12 can be formed by forming an antiferromagnetic film in which the additive metal is added to Cr by plating.
The composition of the antiferromagnetic film is particularly preferably Cr—Mn, Cr—Pt, Cr—Ru or the like.

The antiferromagnetic film of the alloy can be preferably formed using a plating method.
The plating of the antiferromagnetic film may be either electrolytic plating or electroless plating. Electroplating is preferred when the antiferromagnetic film is a Cr-based alloy.
As a specific bath composition, a chloride bath or a sulfate bath is used. For example, a mixed bath of chromium chloride and manganese chloride or a mixed bath of chromium sulfate and manganese sulfate is preferable. The concentration is preferably from 0.01 to 1.0 mol / L, particularly preferably from 0.1 to 0.8 mol / L. A weak acidity with a pH of 1 to 5 is good. The current density is preferably 5 A / dm ² or more and 60 A / dm ² or less. As the complexing agent, organic amines such as glycine, ammonium salts such as ammonium sulfate, and boric acid are preferable.
The thickness of the antiferromagnetic film is preferably 2 to 50 nm, more preferably 5 to 20 nm. The antiferromagnetic film may be polished so as to have a desired surface roughness using colloidal silica or the like.

The antiferromagnetic film of the metal oxide film other than natural oxidation is preferably an oxide of at least one metal selected from the group consisting of Co, Ni, and Fe. For example, NiFeO, CoNiFeO {CoNiFeO _x (x Is a positive number)}.
An antiferromagnetic film of a metal oxide film other than natural oxidation can be obtained by oxidation of at least one soft magnetic film constituting a soft magnetic underlayer.
When the soft magnetic film is a NiFe permalloy film, it is Ni (Fe) O when oxidized, and the oxide film exhibits antiferromagnetism. When the soft magnetism is a CoNiFe film, it is CoNiFeO _x (x is a positive number) when oxidized, and in this case also becomes an antiferromagnetic film.
The oxidation of the antiferromagnetic film may be performed by wet oxidation in a solution containing an oxidizing agent (H ₂ O ₂ or the like) during the wet plating process, or dry oxidation (preferably in the atmosphere or under atmospheric control after plating) (Ozone oxidation).

The thickness of the antiferromagnetic film of the metal oxide film other than natural oxidation is preferably an optimum film that can be controlled between about 2 nm to 50 nm, more preferably about 5 to 20 nm by changing the oxidation conditions. A multilayer magnetic backing layer including a thick antiferromagnetic film can be formed. Although an oxide film having a thickness of 50 nm or more is possible, it is not preferable because the oxidation process takes too much time.
The antiferromagnetic film may be polished so as to have a desired surface roughness using colloidal silica or the like.

  At least one soft magnetic film constituting the soft magnetic underlayer is formed by, for example, a general method known as electroless plating so that the plating film thickness is preferably 100 to 1500 nm, and then the plating film is formed. It is obtained by polishing to a predetermined thickness, preferably 50 to 500 nm. This polishing step is performed using inorganic fine particles such as colloidal silica and ceria, and also serves to control the surface roughness simultaneously with the thickness adjustment.

The soft magnetic underlayer of the present invention is a film having an anisotropy in which the surface inner diameter or circumferential direction is in the direction of easy magnetization. If only the plated soft magnetic film previously filed by the present inventors is used, anisotropy can be imparted by plating in a magnetic field. However, since the multilayer magnetic backing layer of the present invention includes an antiferromagnetic film, the entire layer cannot be made anisotropic only by plating in a magnetic field. Therefore, anisotropy is performed by heat treatment in a magnetic field after plating.
The heat treatment in a magnetic field starts from a temperature slightly above the antiferromagnetic film nail point of the multilayer magnetic backing layer (for example, 10 to 100 ° C.), and gradually cools to give circumferential or radial anisotropy to the entire layer. It becomes possible to grant. The magnetic field may be applied to 100 oersted (Oe) or more up to several kOe.

As the magnetic circuit for applying the magnetic field, for example, magnetic circuits as shown in FIGS. 3A and 4A can be used. A gap formed by opposing the magnet side surfaces perpendicular to the magnetic pole surfaces 84 and 94 is a magnetic field application space. In the magnetic circuit, a magnetic field opposite to the magnetization directions 81 and 91 of the permanent magnets 82 and 92 is generated at a position equidistant from the two opposing surfaces on a straight line connecting the intersections of diagonal lines of opposing magnet side surfaces. be able to.
The magnetic field application direction of the substrates to be processed 83 and 93 can be selected by properly using the two types of magnetic circuits shown in the figure. FIG. 3A shows a radial magnetic field, and FIG. 4A shows a circumferential magnetic field application. When a magnetic field is applied in the intermediate direction between the radial direction and the circumferential direction, the permanent magnet may be arranged so that the magnetization direction is in the intermediate direction.
As shown in FIGS. 3 (b) and 4 (b), a plurality of pairs of magnets 82 and 92 are stacked using a nonmagnetic support plate 88, and a plurality of gaps are provided to cover a narrow point of the processing gap. On the other hand, since the magnetic circuit is provided in the vicinity of the substrates 83 and 93 to be processed, the magnetic circuit may be relatively small.

When a magnetic field is generated in the radial direction, one or a plurality (2 to 40) of permanent magnets having radial magnetization can be disposed on one surface of the sample. When arranging a plurality, it is preferable to arrange them evenly.
When forming a magnetic field in the circumferential direction, one or a plurality (2 to 6) of permanent magnets having circumferential magnetization can be arranged on one surface of the sample. When a plurality of magnets are arranged, as shown in FIG. 4A, it is desirable that the magnets are arranged at intervals on the same sample surface so as not to interfere with each other or to short-circuit between the magnets. . The intervals are preferably uniform.

When one permanent magnet having radial magnetization or circumferential magnetization is arranged to generate a magnetic field in the radial direction or circumferential direction, for example, the magnetic circuit shown in FIGS. 5A and 5B is used. be able to. 5 (a) and 5 (b), the virtual center axis 87 of the magnetic circuit and the support rod 86 that penetrates and fixes the center position of the unprocessed sample 93 set in advance are matched, By rotating 96, the axisymmetric magnetic field can be applied to any point on the concentric circumference of the untreated sample when viewed in terms of time average. The magnet side surface is indicated by 95.
The “virtual central axis of the magnetic circuit” refers to the center of the magnetic circuit in which magnets are formed at radial positions from the center point.

The rotation 96 in the magnetic field is performed together with the heat treatment, and the heat treatment step is usually performed slowly over 5 minutes to several hours. Therefore, if the rotation is relatively performed at a rotational speed of 5 rpm to 500 rpm, It can be considered that an axially symmetric magnetic field was applied. If the rotational speed is less than 5 rpm, the time-average axial symmetry may not be obtained, and if the rotational speed exceeds 500 rpm, the rotational mechanism may be complicated and difficult. The preferable lower limit of the rotation speed is 10 rpm, and the preferable upper limit is 150 rpm.
In the above rotation, either the substrate to be processed or the magnetic circuit may be rotated, or both may be rotated in opposite directions, but it is preferable to rotate the untreated sample from the viewpoint of workability.

When magnetic anisotropy is imparted by rotation in the magnetic field, the permanent magnet to be arranged may be provided with a notch 85 as shown in FIG.
By providing the cutout portion 85, the support rod 86 can be set to coincide with the virtual central axis 87 of the magnetic circuit after the support rod 86 is inserted into the untreated sample, thereby improving workability. Can do.
When magnetic anisotropy is imparted using the above rotation, the number of permanent magnets arranged on the same sample surface may be one or plural.

Conventionally, heat treatment in a magnetic field is performed by providing a heat treatment furnace made up of non-magnetic furnace parts inside a magnetic field generation means made up of a magnetic circuit composed of an electromagnet, a permanent magnet, a superconducting magnet, etc. However, there is a problem that the magnetic field generating means becomes large regardless of which apparatus is used, and the heat treatment furnace tends to have a complicated configuration.
Therefore, as a heat treatment apparatus in a magnetic field, a heat resistant magnetic circuit may be used for the convenience of disposing a magnetic circuit inside the heat treatment furnace.
The temperature of the heat treatment in the magnetic field varies depending on the material of the substrate to be processed, but is generally approximately 150 ° C. or higher and 350 ° C. or lower. The magnetic circuit also hardly thermally demagnetizes in this temperature range, that is, irreversible demagnetization (initial demagnetization) is preferably 5% or less, more preferably 1% or less.
The inside of the furnace for heat treatment in a magnetic field is usually an inert gas atmosphere such as Ar, He, or nitrogen.
In the present specification, the irreversible demagnetization (initial demagnetization) refers to demagnetization at the initial stage of holding, and represents the reduction rate of the magnetic field strength at the point of holding for 1 hour by applying heat. Is a value measured using.

  A permanent magnet magnetic circuit as shown in FIG. 6 is inserted into the furnace, the soft magnetic film backing layer-formed substrate of the present invention is held in the gap between the magnets, and heat treatment is performed while rotating the substrate. Depending on the direction of magnetic field application to the substrate, radial and circumferential anisotropy can be created separately.

The magnetic recording layer may be formed directly on the soft magnetic underlayer, but various intermediate films are provided as necessary for the purpose of matching the crystal grain size and the magnetic characteristics. You may make it form on top.
As the intermediate film, for example, a Ru film, a Re film, or the like is used. Further, a plurality of interlayer films may be laminated.
The thickness of the intermediate film is preferably 2 to 25 nm.

The magnetic recording layer provided on the soft magnetic backing layer is made of a hard magnetic material for performing perpendicular magnetization recording.
The composition of the magnetic recording layer is not particularly limited as long as it is a hard magnetic material capable of forming a magnetic domain easily magnetized in a direction perpendicular to the layer surface. When the sputtering method is used, for example, a Co—Cr alloy film, an Fe—Pt alloy film, a CoCrPt—SiOx granule film, a Co / Pd multilayer film, or the like can be used.
The thickness of the magnetic recording layer is preferably about 5 to 100 nm, more preferably about 10 to 50 nm. The magnetic recording layer is formed so that its coercive force is preferably 2 to 10 kOe, more preferably 3 to 6 kOe.

The protective layer provided on the top surface of the magnetic recording layer can be formed of a material that has been used in conventional magnetic recording media. For example, a crystalline protective film such as alumina (Al ₂ O ₃ ) as well as an amorphous carbon protective film formed by sputtering or CVD can be used. The thickness of the protective layer is, for example, about 2 to 10 nm.

  A lubricating layer is provided on the upper surface of the protective layer. The lubricating layer can also be formed by applying a material used for a conventional magnetic recording medium, and there is no particular limitation on the type of agent and the application method. For example, the lubricating layer is formed by applying a fluorinated oil or fat to form a monomolecular film. The thickness of the lubricating layer is, for example, about 2 to 10 nm.

Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.
Examples 1-4
In this example, a single crystal Si substrate was used as the nonmagnetic substrate. From a single crystal of 200 mm (8 inches) in diameter grown by the CZ method, core removal, centering, and lapping are performed, and a (100) Si single crystal plate having an outer diameter of 48 mm and an inner diameter of 12 mm (P-doped n-type) ) This Si single crystal plate was polished on both sides using a slurry containing colloidal silica having an average particle size of 15 nm to obtain a Si substrate having a surface roughness (Rms) of 4 nm. In addition, Rms is a square average roughness, and was measured using AFM (atomic force microscope).
The Si substrate was immersed in a 2% by weight aqueous caustic soda solution (liquid temperature: 45 ° C.) for 3 minutes to remove the thin surface oxide film on the substrate surface, and surface activation treatment for etching Si on the extreme surface was performed. Subsequently, in order to form a nucleation film, a base plating bath prepared by adding 0.5N of ammonium sulfate to a 0.1N nickel sulfate aqueous solution was prepared and immersed for 5 minutes in a bath maintained at a liquid temperature of 80 ° C. A layer was obtained. Alternatively, a nonmagnetic nucleation film was formed by the following procedure. The substrate surface is hydrophilized by immersing in an aqueous solution (liquid temperature: 45 ° C.) containing 0.5 mol / L sodium hydroxide and 1 mol / L H ₂ O ₂ for 10 minutes. After washing thoroughly, a mixed bath of 0.1M nickel sulfate, 0.5M ammonium sulfate, and 0.1M sodium citrate was prepared for subsequent formation of a non-magnetic nucleation film, and 0.1M hypochlorous acid as a reducing material was prepared. Na phosphate was added and the substrate was immersed in a bath maintained at a liquid temperature of 80 ° C. and a pH of 7 to 7.5 for 2 minutes to obtain a nonmagnetic nucleation film.

Next, for forming a soft magnetic film, a plating solution containing ammonium sulfate 0.2N, nickel sulfate 0.02N, cobalt sulfate 0.1N, iron sulfate 0.01N, and dimethylamine borane 0.04N as a reducing agent was prepared. The liquid temperature was heated and maintained at 65 ° C. The reason for setting the liquid temperature to 65 ° C. is that the film growth rate when the soft magnetic film is electrolessly plated is 0.1 μm / min. While the Si substrate was rotated at 60 rpm, plating was performed for 10 minutes each to obtain a Co—Ni—Fe soft magnetic film above the underlying plating layer. Alternatively, a mixed bath of 0.07M nickel sulfate, 0.03M iron sulfate, 0.5M ammonium sulfate, and 1M sodium citrate is prepared, 0.05M dimethylamine borane is added as a reducing material, the liquid temperature is 65 ° C., pH 7 The substrate was immersed in a bath maintained at ˜8 for 15 minutes while rotating at 60 rpm to obtain a Ni—Fe-based soft magnetic film. The obtained composition was approximately Co ₇₀ Ni ₁₃ Fe ₁₇ or Ni ₈₀ Fe ₂₀ (atomic ratio) and contained 1 to 2 at% of S, C and B derived from the reducing agent. In the multilayer soft magnetic film, the thickness was added for each film layer.

To form an antiferromagnetic film, a mixed bath of 0.5M chromium chloride, 0.05M manganese chloride, 1M ammonium sulfate, 1M glycine and 0.5M boric acid is prepared and kept at a liquid temperature of 30 ° C. and pH 2-3. In this bath, the substrate was placed on the cathode and electrodeposited at a current density of 20 A / dm ² to obtain an antiferromagnetic film mainly composed of 15 nm of Cr—Mn. A mixed bath of 0.5 M chromium chloride, 0.01 M ruthenium chloride, 1 M ammonium sulfate, 1 M glycine and 0.5 M boric acid was prepared, and the substrate was placed in a bath maintained at a liquid temperature of 30 ° C. and a pH of 2 to 3. It was placed on the cathode and electrodeposited at a current density of 10 A / dm ² to obtain an antiferromagnetic film mainly composed of 15 nm Cr—Ru.

A Si substrate with a soft magnetic backing layer formed thereon is applied with a static magnetic field in the radial direction of 1 kilo-Oersted (kOe) and held at a temperature 20 ° C. to 70 ° C. (200 ° C. to 250 ° C.) for 1 hour. And cooling in a magnetic field continuously to 100 ° C. at a rate of 0.5 ° C./min. The uppermost soft magnetic film of the obtained soft magnetic layer was polished with colloidal silica, and the thickness of the entire soft magnetic backing layer was adjusted to 100 to 500 nm. The results of measuring the magnetization curve by the Kerr effect for the polishing film are summarized in Table 1. In addition, magnetic domain observation was performed on the obtained polished surface by the Kerr effect, but no clear magnetic domain was observed. FIG. 7 shows an example of the noise measurement result of the radial anisotropic film. However, in this example, a part of the domain wall was observed on the inner diameter side due to the influence of the inner diameter holding jig, but this could be eliminated by improving the jig. The difference in magnetization saturation magnetic field strength of the surface radially inwards and (H _d) in-plane circumferential direction of the magnetization saturation magnetic field strength _{(H c) (δH = H} d -H c) is 10 Oe or more (generally about 15 to 20 oersteds) Anisotropy of is obtained. The coercive force exhibited good soft magnetic characteristics of about 5 Oersted (Oe) or less in any soft magnetic film.

  In Table 1, Sub represents a substrate, NL represents a nucleation film, FM- represents a ferromagnetic film, NM- represents a non-magnetic film, Soft FM- represents a soft magnetic film, SUL represents a soft magnetic backing film, and AFL represents an antiferromagnetic film. . Lamination was performed on the substrate in the order described in the film configuration. The number after the film structure represents the film thickness (nm).

Production Example 1
A perpendicular magnetic recording layer was formed by sputtering on the soft magnetic backing layer obtained in Example 1. As the sputtering conditions, a Ru film was first formed with a thickness of 8 nm while maintaining the substrate temperature at 180 ° C., and Co: Cr: Pt = 76: 19: 5 (mass%) and SiO ₂ were simultaneously sputtered on this Ru film. Thus, a magnetic film having a composition of 12 nm was formed to obtain a magnetic recording layer. The coercive force of this magnetic recording layer was 4 kilooersted (kOe) in the direction perpendicular to the film surface. A perpendicular magnetic recording medium was obtained by coating the magnetic recording layer with amorphous carbon having a thickness of 8 nm and further applying a fluorine lubricating film by dipping.
After this perpendicular magnetic recording medium was placed on a spin stand and DC erase was performed, writing was performed with a nano slider head with a flying height of 10 nm and the noise level of the reproduced signal was measured. As a result, spike noise was found in the envelope pattern. It was not recognized (FIG. 7). The average level of the S / N ratio was as good as 24 dB. When the antiferromagnetic film is not inserted, spike noise is observed, but it has been found that it can be suppressed by the configuration of the present invention.

Examples 5-11
In this example, a single crystal Si substrate was used as the nonmagnetic substrate. From a single crystal of 200 mm (8 inches) in diameter grown by the CZ method, core removal, centering, and lapping are performed, and a (100) Si single crystal plate having an outer diameter of 48 mm and an inner diameter of 12 mm (P-doped n-type) ) This Si single crystal plate was polished on both sides using a slurry containing colloidal silica having an average particle size of 15 nm to obtain a Si substrate having a surface roughness (Rms) of 4 nm. In addition, Rms is a square average roughness, and was measured using AFM (atomic force microscope).
The Si substrate was immersed in a 2% by weight aqueous caustic soda solution (liquid temperature: 45 ° C.) for 3 minutes to remove the thin surface oxide film on the substrate surface, and surface activation treatment for etching Si on the extreme surface was performed. Subsequently, in order to form a nucleation film, a base plating bath prepared by adding 0.5N of ammonium sulfate to a 0.1N nickel sulfate aqueous solution was prepared and immersed for 5 minutes in a bath maintained at a liquid temperature of 80 ° C. A layer was obtained. Alternatively, a nonmagnetic nucleation film was formed by the following procedure. The substrate surface was hydrophilized by immersing in an aqueous solution (liquid temperature: 45 ° C.) containing 0.5 mol / L of caustic soda and 1 mol / L of H ₂ O ₂ for 10 minutes. After washing thoroughly, a mixed bath of 0.1M nickel sulfate, 0.5M ammonium sulfate, and 0.1M sodium citrate was prepared for subsequent formation of a non-magnetic nucleation film, and 0.1M hypochlorous acid as a reducing material was prepared. NaP was added, and the substrate was immersed in a bath maintained at a liquid temperature of 80 ° C. and a pH of 7 to 7.5 for 2 minutes to obtain a NiP nonmagnetic nucleation film.

Next, for forming a soft magnetic film, a plating solution containing ammonium sulfate 0.2N, nickel sulfate 0.02N, cobalt sulfate 0.1N, iron sulfate 0.01N, and dimethylamine borane 0.04N as a reducing agent was prepared. The liquid temperature was heated and maintained at 65 ° C. The reason for setting the liquid temperature to 65 ° C. is that the film growth rate when the soft magnetic film is electrolessly plated is 0.1 μm / min. While the Si substrate was rotated at 60 rpm, plating was performed for 10 minutes each to obtain a Co—Ni—Fe soft magnetic film above the underlying plating layer. The obtained composition was approximately Co ₇₀ Ni ₁₃ Fe ₁₇ (atomic ratio) and contained 1 to 2 at% of S, C, and B derived from the reducing agent. In the multilayer soft magnetic film, the thickness was added for each film layer.
Alternatively, a mixed bath of 0.07 M nickel sulfate, 0.03 M iron sulfate, 0.5 M ammonium sulfate and 0.1 M sodium citrate is prepared, 0.05 M dimethylamine borane is added as a reducing agent, and the liquid temperature is 65 ° C. The substrate was immersed in a bath maintained at pH 7 to 8 for 15 minutes while rotating at 60 rpm to obtain a Ni—Fe based soft magnetic film. The resulting composition was generally Ni80Fe20 (atomic ratio) and contained 1-2 at% of S, C, and B derived from the reducing agent. In the multilayer soft magnetic film, the thickness was added for each film layer.

Oxide films were formed either wet or dry for the formation of antiferromagnetic films.
Wet deposition is washed with water after the soft magnetic film forming, further H ₂ O ₂ added to before and after immersion for 10 minutes in warm water to oxidize the soft magnetic layer surface, by changing the H ₂ O ₂ amount and temperature An oxide film having a thickness of about 10 to 15 nm was formed. If necessary, a soft magnetic film was further formed and multilayered.
In the dry film formation, the soft magnetic film was plated, washed with water and dried, and the plated substrate was heated and oxidized (180 to 250 ° C.) in an oxidizing atmosphere or an ozone atmosphere to form an oxide film. The oxide film thickness was controlled by the amount of oxidizing gas and the heat treatment temperature, and the oxide film was approximately 10 nm to 15 nm.
When high smoothness was required, the oxidation treatment was performed after polishing the soft magnetic film.

A 1 kOe static magnetic field is applied to the Si substrate on which the soft magnetic underlayer has been formed, held for 1 hour at a temperature 20 ° C. above the Neel temperature, and then continuously magnetic at a rate of 0.5 ° C./min up to 100 ° C. Medium cooling was performed. The obtained soft magnetic film was polished with colloidal silica, and the thickness of the soft magnetic backing layer was adjusted to 100 to 500 nm. The results of measuring the magnetization curve by the Kerr effect for the polishing film are summarized in Table 1. Further, magnetic domain observation was performed on the obtained polished surface by the Kerr effect, but no clear magnetic domain was observed. FIG. 8 shows an example of the magnetic domain measurement result of the circumferentially anisotropic film. However, in this example, a part of the domain wall was observed on the inner diameter side due to the influence of the inner diameter holding jig, but this could be eliminated by improving the jig. Magnetization saturation magnetic field strength surface inner diameter direction (H _d) in-plane circumferential direction of the difference between the magnetization saturation magnetic field strength _{(H c) (δH = H} d -H c) is approximately 10 oersted (Oe) or more anisotropic Is obtained. The coercive force showed good soft magnetic characteristics of about 5 oersted or less in any soft magnetic film.

  In Table 2, Sub represents a substrate, NL represents a nucleation film, FM- represents a ferromagnetic film, NM- represents a non-magnetic film, Soft FM- represents a soft magnetic film, SUL represents a soft magnetic backing film, and AFL represents an antiferromagnetic film. . Lamination was performed on the substrate in the order described in the film configuration. The number after the film structure represents the film thickness (nm).

Production Example 2
A perpendicular magnetic recording layer was formed by sputtering on the soft magnetic backing layer obtained in Example 7. As the sputtering conditions, a Ru film was first formed with a thickness of 8 nm while maintaining the substrate temperature at 180 ° C., and Co: Cr: Pt = 76: 19: 5 (mass%) and SiO ₂ were simultaneously sputtered on this Ru film. Thus, a magnetic film having a composition of 12 nm was formed to obtain a magnetic recording layer. The coercive force (VSM) of this magnetic recording layer was 4 kOe in the direction perpendicular to the film surface. A perpendicular magnetic recording medium was obtained by coating the magnetic recording layer with amorphous carbon having a thickness of 8 nm and further applying a fluorine lubricating film by dipping.
The perpendicular magnetic recording medium was placed on a spin stand and subjected to DC erase, and then the reproduction signal was measured by writing with a nano slider head having a flying height of 10 nm. No spike noise was observed in the envelope pattern. Moreover, the average level of the S / N ratio was as good as 23 dB. No spike noise was observed when the same film was formed on other soft magnetic underlayers.

Comparative production example 1
In the film configuration of Example 7, the same 10 nm film was formed by sputtering using Cr as an antiferromagnetic film instead of the antiferromagnetic film NiO. The Neel temperature of Cr was 312K (38 ° C.), and since the Neel temperature was low, a sufficient exchange coupling force could not be obtained, and spike noise was observed in the media on which the recording film was formed.

  The present invention provides a substrate suitable for the manufacture of a perpendicular magnetic recording medium having low noise and good signal reproduction characteristics, and a method for manufacturing the same.

1 is a schematic cross-sectional view for explaining a basic layer structure of a perpendicular two-layer magnetic recording medium of the present invention using a Si substrate as a nonmagnetic substrate and provided with a nucleation film. It is a conceptual diagram of the various multilayer soft-magnetic backing layer provided in the board | substrate for magnetic recording media of this invention. (A) is a schematic perspective view showing an embodiment of the magnetic circuit of the present invention in which permanent magnets are arranged so that the magnetic field direction in the gap between the magnets is axially symmetric in the radial direction, and (b) is unprocessed. It is sectional drawing in the BB cross section of the magnetic circuit shown to (a) in the state which set the sample to the magnetic circuit through the support rod. (A) is a schematic perspective view showing one embodiment of the magnetic circuit of the present invention in which permanent magnets are arranged so that the magnetic field direction in the gap between the magnets is axially symmetric in the circumferential direction, and (b) is unprocessed. It is sectional drawing in the BB cross section of the magnetic circuit shown to (a) in the state which set the sample to the magnetic circuit through the support rod. It is a typical perspective view which shows the one aspect | mode of the magnetic circuit of this invention which can provide an axially symmetric anisotropy to (a) radial direction or (b) circumferential direction by rotating a sample. It is an example of the magnetic circuit used for the heat processing in the magnetic field of the board | substrate for magnetic recording media of this invention. It is an example of soft magnetic underlayer noise measurement of the magnetic recording medium substrate of the present invention (data for one track of the radially anisotropic soft magnetic underlayer). An example of magnetic domain observation (circumferential anisotropy) by the Kerr effect of the magnetic recording medium substrate of the present invention is shown. It is the cross-sectional schematic explaining the general laminated structure of a horizontal magnetic recording system hard disk. 1 is a schematic cross-sectional view for explaining the basic layer structure of a perpendicular double-layer magnetic recording medium in which a recording layer for perpendicular magnetic recording is provided on a soft magnetic underlayer.

Explanation of symbols

1, 101, 111 Non-magnetic substrate 2 102, 112 Nucleation film 3, 103, 113 Soft magnetic backing layer 4 Intermediate film 5, 105, 115 Magnetic recording layer 6, 106, 116 Protective layer 7, 107, 117 Lubricating layer 81a , 81b, 91 Magnetization direction 82, 92 Permanent magnet 83, 93 Processed substrate 84, 94 Magnetic pole surface 85 Notch 86 Support rod 87 Virtual center axis 88 of magnetic circuit Nonmagnetic support plate 95 Magnet side surface 96 Sample rotation direction

Claims (8)

  A magnetic recording medium substrate having a soft magnetic backing layer on a disc-shaped nonmagnetic substrate having a diameter of 90 mm or less and having a center hole, wherein the soft magnetic backing layer uses a plating method in any order. And a magnetic recording medium substrate having at least one soft magnetic film and at least one antiferromagnetic film, and having circumferential or radial magnetic anisotropy.   At least one of the antiferromagnetic films is a film of an alloy containing Cr or Mn or a metal oxide film other than natural oxidation, exchange coupled with the soft magnetic film, and having a Neel temperature of 100 ° C. or higher. The magnetic recording medium substrate according to claim 1, wherein the thickness is 5 nm or more and 50 nm or less.   The magnetic recording medium substrate according to claim 2, wherein the metal oxide film is a film obtained by surface-oxidizing at least one of the soft magnetic films.   A method for manufacturing a substrate for a magnetic recording medium having a soft magnetic backing layer on a disk-shaped nonmagnetic substrate having a diameter of 90 mm or less and having a center hole, either of which can be performed first, using a plating method Forming a soft magnetic backing layer comprising at least one step of forming a soft magnetic film and at least one step of forming an antiferromagnetic film, and circumferential or radial magnetic anisotropy in the soft magnetic backing layer The manufacturing method of the board | substrate for magnetic recording media including the process of providing.   5. The method for manufacturing a magnetic recording medium substrate according to claim 4, wherein at least one of the steps of forming the diamagnetic film is performed using a plating method.   5. The method for manufacturing a substrate for a magnetic recording medium according to claim 4, wherein at least one of the steps of forming the antiferromagnetic film includes oxidizing the surface of the soft magnetic film formed by using the plating method.   The method for producing a substrate for a magnetic recording medium according to claim 6, wherein the surface of the soft magnetic film formed by using the plating method is oxidized in an oxidizing agent solution or in an oxidizing atmosphere.   A perpendicular recording medium using the magnetic recording medium substrate according to claim 1.