JP2009223989A - Nano-hole structure and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nano-hole structure and a magnetic recording medium capable of exhibiting soft magnetic characteristics without increasing coercive force due to shape magnetic anisotropy, thereby obtaining a sufficient recording magnetic field. <P>SOLUTION: The nano-hole structure includes a substrate and a nano-hole having a prescribed depth from a surface of the substrate and having a diameter at a bottom side larger than that at the surface side. It is preferable that the nano-hole includes a first region having a first length from the surface of the substrate and a second region at a bottom side from the first region, the second region having a diameter larger than that of the first region and having a second length to the bottom. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention is suitable for a nanohole structure suitable for a magnetic recording medium and the like, a hard disk device widely used as a computer external storage device, a consumer video recording device, and the like, and has a large capacity and high speed recording. The present invention relates to a magnetic recording medium capable of recording.

  As a next-generation ultra-high-density perpendicular magnetic recording medium, so-called patterned media that improve the bit density by reducing the magnetic interaction between them by separating and arranging magnetic materials that carry individual signals (magnetic bits) Is attracting attention. In the case of patterned media, the size of each magnetic material needs to be on a nanometer scale, and the development of a method for producing a nanostructured magnetic material having a desired size and magnetic properties is the key to realization.

  As a method for producing a nano-sized structure, for example, there is a method of directly manufacturing using a fine pattern forming technique such as a photolithography method or an electron beam exposure method. However, these methods have processing accuracy limitations and throughput problems. On the other hand, a novel nanostructure formation method based on a self-organized structure is also being studied. This method is considered to have the possibility of enabling a very fine structure in a wider range, faster and cheaper than before, and many studies have been made.

  One of the methods using such self-organization is anodic oxidation, which can produce a nanohole-containing structure with good controllability and low cost. For example, when anodizing Al and its alloys in an acid solution, a porous oxide film is obtained, in which uniform nanoholes having a very high aspect ratio of about 10 nm to several hundred nm in diameter are about 20 nm to several nm. A characteristic structure of uniform arrangement at intervals of 100 nm is realized (FIG. 1).

  The interval, diameter, and depth of the nanoholes can be controlled by the applied voltage at the time of anodizing, the anodizing time, and the like, and nanoholes can be regularly arranged by a so-called imprint method. Further, it is known that each nanohole can be filled with a magnetic material, and shape magnetic anisotropy is manifested due to its high aspect ratio. Therefore, a nanohole array filled with a magnetic material can be said to be a promising candidate for vertical patterned media.

In the perpendicular patterned media, it is generally known that the introduction of a soft magnetic underlayer under the recording layer is effective for obtaining a sufficient recording magnetic field at the time of recording. Is also known to hold (for example, Non-Patent Document 1).
For example, although a nanohole structure having a structure as shown in FIG. 7 has been proposed, the thickness of the hard magnetic layer is thick and the soft magnetic underlayer is not patterned so as to be separated, so that the magnetic field is concentrated. There is a problem that the soft magnetic properties cannot be fully exhibited.

  In order to make the soft magnetic property sufficiently effective, there is a method of filling a nanohole with a soft magnetic material (for example, Patent Documents 1 and 2). As shown in FIG. 8, the introduction of the hard magnetic / soft magnetic multilayer structure into the nanohole allows the thickness of the hard magnetic layer to be reduced and the soft magnetic layer is separated and patterned. Since the effect of promoting magnetization reversal by the external magnetic field of the filled magnetic material is brought about while maintaining heat fluctuation resistance, there is an advantage from the viewpoint of magnetic property control and media design.

  However, since nanoholes are formed with a certain depth, the soft magnetic material filled in the nanoholes actually increases the coercive force due to shape magnetic anisotropy and cannot exhibit soft magnetic properties. Can happen. In this case, in order to exhibit the soft magnetic characteristics, the soft magnetic region needs to have a sufficient thickness, and it is difficult to cope with it by simply reducing the layer thickness. Also, reducing the shape anisotropy by remarkably increasing the hole diameter of the nanohole means an increase in the recording dot size, which is undesirable because it increases magnetostatic interaction between adjacent dots, recording synchronization and reproduction errors. .

H. Oshima et al., IEEE Trans Magn. 43, 2148 (2007) JP 2004-084193 A JP 2006-277844 A

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, an object of the present invention is to provide a nanohole structure and a magnetic recording medium that can exhibit soft magnetic characteristics without increasing coercive force due to shape magnetic anisotropy, and thereby obtain a sufficient recording magnetic field. And

Means for solving the problems are as follows. That is,
The nanohole structure of the present invention includes a base material, and a nanohole having a predetermined depth from the surface of the base material and having a diameter larger on the bottom side than on the surface side. Features.
In the nanohole structure, a nanohole having a predetermined depth from the surface of the base material and having a diameter larger on the bottom side than on the surface side is formed on the base material. By introducing a hard magnetic material into the portion with a small diameter and introducing a soft magnetic material into a portion with a large diameter on the bottom side of the nanohole, the soft magnetic characteristics can be improved without increasing the coercive force due to shape magnetic anisotropy. Thus, a sufficient recording magnetic field can be obtained.

The magnetic recording medium of the present invention includes a substrate, a base material formed on the substrate, a nanohole having a predetermined depth from the surface of the base material, and having a diameter larger on the bottom side than on the surface side. And a hard magnetic material filled in the nanohole.
In the magnetic recording medium, since a nanohole having a predetermined depth from the surface of the base material and having a larger diameter on the bottom side than the surface side is formed on the base material formed on the substrate, Introducing a hard magnetic material into a portion with a small diameter on the surface side of the substrate and introducing a soft magnetic material into a portion with a large diameter on the bottom side of the nanohole increases the holding force due to shape magnetic anisotropy. Therefore, the soft magnetic characteristics can be exhibited, and a sufficient recording magnetic field can be obtained.

  According to the present invention, conventional problems can be solved, soft magnetic characteristics can be exhibited without increasing coercive force due to shape magnetic anisotropy, and a sufficient recording magnetic field can be obtained. Nanohole structures and magnetic recording media can be provided.

(Nanohole structure)
As the nanohole structure, besides having a base material and nanoholes, the material, shape, structure, size and the like can be appropriately selected according to the purpose.

  The material for the base material is not particularly limited and can be appropriately selected depending on the purpose, and may be any of a simple metal, an oxide thereof, a nitride, an alloy, etc. Among them, for example, Alumina (aluminum oxide), aluminum, glass, silicon and the like are particularly preferable.

There is no restriction | limiting in particular as said shape, According to the objective, it can select suitably, For example, plate shape, disk shape (disk shape), etc. are mentioned suitably. Among these, when the nanohole structure is applied to a magnetic recording medium such as a hard disk, a disk shape (disk shape) is preferable.
In addition, when the said shape is the said plate shape, disk shape, etc., the said nanohole (pore) is formed in the direction substantially orthogonal to these one exposed surface (plate surface).

There is no restriction | limiting in particular as said structure, Although it can select suitably according to the objective, For example, a single layer structure may be sufficient and a laminated structure may be sufficient.
The size is not particularly limited and can be appropriately selected according to the purpose. For example, when the nanohole structure is applied to a magnetic recording medium such as a hard disk, the size of an existing hard disk or the like is not limited. When the nanohole structure is applied to a DNA chip or the like, the size corresponding to the size of an existing DNA chip or the like is preferable. When applied to a catalyst substrate such as a nanotube, a size corresponding to the field emission device is preferable.

The nanohole is not particularly limited as long as it has a predetermined depth from the surface of the substrate and has a larger diameter on the bottom side than on the surface side, and can be appropriately selected according to the purpose.
Here, the nanohole has a first region having a first length from the surface of the base material and a diameter larger than the first region on the bottom side of the first region, and the second region extends to the bottom. It is preferable that the 2nd area | region which has length is included. The sum of the first length and the second length is preferably equal to the predetermined depth. Preferably, the first region is filled with a hard magnetic material, and the second region is filled with a soft magnetic material. The magnetic material filled in the first region is appropriately selected according to the purpose, and may be a hard magnetic material or a soft magnetic material.

As shown in FIG. 2, the nanohole is formed into two layers in the depth direction, the nanohole region 1 and the nanohole region 2 have different hole diameters, and the hole diameter 31 of the nanohole region 2 on the bottom side is the surface side layer. It is larger than the hole diameter 30 of the nanohole region 1. If the hole diameter 31 of the nanohole region 2 on the bottom side is made sufficiently large, the magnetic region filled in the nanohole region 2 can maintain soft magnetic characteristics without increasing coercive force due to shape magnetic anisotropy. Can do. Therefore, the nanohole region 2 can have a function as a soft magnetic backing layer, and as a result, a sufficient recording magnetic field can be obtained.
The nanohole may be formed as a hole penetrating the nanohole structure, or may be formed as a hole (dent) without penetrating the nanohole structure. For example, the nanohole structure Is used as the magnetic recording medium, the nanohole is preferably formed as a through hole penetrating the nanohole structure.

The arrangement of the nanoholes is not particularly limited and can be appropriately selected depending on the purpose.For example, the nanoholes may be arranged in parallel in one direction, or arranged in at least one of concentric and spiral shapes. It may be. The former arrangement is preferable when the nanohole structure is applied to a DNA chip or the like, and the latter arrangement is preferable when the nanohole structure is applied to the magnetic recording medium such as a hard disk or a video disk. In the case of use, a concentric shape is preferable from the viewpoint of easy access, and in the case of video disk use, a spiral shape is preferable from the viewpoint of easy continuous reproduction.
When the nanohole structure is suitable for the magnetic recording medium such as a hard disk, it is preferable that the nanoholes in adjacent nanohole arrays are arranged in the radial direction. In this case, the magnetic recording medium is capable of high-density recording and high-speed recording without increasing the write current of the magnetic head, has a large capacity, has excellent overwrite characteristics, and has uniform characteristics. There is no problem of light etc. and it is extremely high quality.

  The width of the nanohole array is not particularly limited and may be appropriately selected depending on the purpose. For example, when the nanohole structure is suitable for the magnetic recording medium such as a hard disk, tracking is easily performed. In that, when one array is a data area and another array adjacent to the array is a guard band area, the ratio of the width of the data area to the guard band area is 2: 1. Is preferred. Specifically, the array width suitable for the data region is preferably 15 to 200 nm, for example, and the array width suitable for the guard band region is preferably 7 to 100 nm, for example.

  The arrangement pattern of the nanoholes in the arrangement of the nanoholes is not particularly limited and can be appropriately selected according to the purpose. However, at least one of the adjacent arrangements is the closest packed in a hexagonal close-packed lattice shape. It is preferable that the pattern is formed as a result. Since the hexagonal close-packed lattice is the most stable pattern in alumina nanoholes, fluctuations in the pattern other than the intentionally introduced pattern change can be minimized.

There is no restriction | limiting in particular as an opening diameter (hole diameter 30) of the 1st area | region in the said nanohole, Although it can select suitably according to the objective, For example, when applying the said nanohole structure to magnetic recording media, such as a hard disk The hard magnetic layer (ferromagnetic layer) is preferably large enough to have a single magnetic domain. Specifically, it is preferably 2/3 or less of the pitch of the nanoholes, more preferably 1/3 to 2/5. . For example, when the pitch of the nanoholes is 30 nm, 20 nm or less is preferable, and 10 to 12 nm is more preferable.
If the aperture diameter in the nanohole exceeds 2/3 of the nanohole pitch, for example, 20 nm when the pitch is 30 nm, the magnetic recording medium to which the nanohole structure is applied may not have a single domain structure.

There is no restriction | limiting in particular as ratio (depth 21 / hole diameter 31) of the depth 21 and the hole diameter 31 in the 2nd area | region in the said nanohole, Although it can select suitably according to the objective, It is 5 or less. preferable.
Shape magnetic anisotropy is caused by the effect of a demagnetizing field. The demagnetizing factor depends on the ratio (aspect ratio) between the height and the diameter of the cylindrical magnetic body, and the demagnetizing factor in the column direction of the cylindrical magnetic body becomes a value that can be almost ignored when the aspect ratio is about 5. Actually, for example, in an experiment in which Co is filled in a nanohole as a magnetic material, it has been confirmed that perpendicular magnetic anisotropy rises at an aspect ratio of 5 or more (for example, H. Kikuchi et al. IEEE Trans. Magn. 41). 3226 (2005)). Therefore, only the soft magnetic material region (second region) filled in the nanohole is sufficiently reduced to have an aspect ratio of 5 or less, so that the soft magnetic material region is not impaired without any loss of the function as the soft magnetic backing layer. The effect of shape magnetic anisotropy acting on (second region) can be avoided. Specifically, for example, the coercive force of the corresponding region can be reduced from the order of about 1 kOe to about several Oe.

Regarding the relationship between the hole diameter 30 in the first region and the hole diameter 31 in the second region in the nanohole, the hole diameter 31 (SUL hole diameter) in the second region is 1.25 times or more the hole diameter 30 (recording dot diameter) in the first region. It is preferable that
The standard hole diameter of nanoholes is about 1/3 of the pitch of nanoholes. Therefore, when the pitch is 25 nm (corresponding to 1 Tbit / in ² ), the hole diameter 30 (recording dot diameter) in the first region is about 8 nm (a smaller one is preferable). On the other hand, from the estimate by simulation, the film thickness of the soft magnetic underlayer (SUL) is required to be 30 nm or more for a continuous film, and 40 nm or more for nanohole filling. In the case of nanohole filling, in order to realize sufficient soft magnetism, the hole diameter 31 (SUL hole diameter) in the second region needs to be 10 nm or more. From the above, it can be seen that the hole diameter 31 (SUL hole diameter) in the second region is preferably 1.25 times or more the hole diameter 30 (recording dot diameter) in the first region.
Even in the case of higher density (narrow pitch), it is estimated that the above-described relationship between the hole diameter 30 and the hole diameter 31 (FIG. 3) can be reduced as a whole while the relationship is maintained substantially.

The thickness of the nanohole structure is not particularly limited and may be appropriately selected depending on the intended purpose. For example, when the nanohole structure is applied to a magnetic recording medium such as a hard disk, the thickness is preferably 500 nm or less, and 300 nm. The following is more preferable, and 20 to 200 nm is particularly preferable.
When the thickness of the nanohole structure exceeds 500 nm, when the nanohole structure is applied to a magnetic recording medium such as a hard disk, high-density recording cannot be performed even if the underlayer is provided on the magnetic recording medium. In some cases, it is necessary to polish the nanohole structure. In this case, time is required and the cost is high, which may cause quality degradation.

The formation of the nanohole structure is not particularly limited and can be performed according to a known method. For example, after forming a metal material layer (metal layer) by a sputtering method, a vapor deposition method, or the like, the anodic oxidation treatment is performed. This can be done by forming nanoholes. Anodization treatment of aluminum or the like is preferable in that a large number of nanoholes can be formed evenly at almost equal intervals.
The material of the metal layer is not particularly limited as long as it is a metal material capable of forming nanoholes, and can be appropriately selected according to the purpose. For example, a single metal, its oxide, nitride, alloy, etc. Of these, among these, for example, aluminum, aluminum alloys, and oxides thereof are preferable.

  Note that nanoholes formed by anodizing treatment are usually randomly arranged, but a pattern for forming a plurality of regular arrays of nanoholes on the metal layer (desired depressions) before the anodizing treatment. Is preferably formed in advance. In this case, the anodizing treatment is advantageous in that the nanoholes can be efficiently formed only on the pattern.

  The method for forming the pattern is not particularly limited and may be appropriately selected depending on the intended purpose. For example, (1) circular convex portions arranged in a pattern (for example, a hexagonal close-packed lattice) A stamper having, as a surface shape, a pattern in which a plurality of regular arrays (when the nanohole structure is applied to a magnetic disk or the like, the regular array of convex portions is concentrically or spirally arranged) is formed. Imprint transfer onto the surface of a layer (for example, alumina, aluminum, etc.) and form a pattern in which a plurality of circles are regularly arranged in a hexagonal close-packed lattice, (2) a resin layer or a photoresist layer on the metal layer After the formation, patterning is performed on the surface of the metal layer by patterning these by an ordinary photo process or an imprint method using a stamper, and etching process. For example, a method of forming a plurality of regularly arranged is formed a pattern of recesses formed by arranging in a hexagonal close-packed lattice pattern), it is preferably exemplified like.

  The stamper is not particularly limited and may be appropriately selected depending on the purpose. From the viewpoint that it is most widely used as a material for producing a fine structure in the semiconductor field, silicon, a silicon oxide film, and the like. From the viewpoint of continuous use durability, a silicon carbide substrate and the like are included, and a Ni stamper used for molding an optical disk and the like is also included. The stamper can be used multiple times. There is no restriction | limiting in particular as the method of the said imprint transfer, According to the objective, it can select suitably from well-known methods. The resist material for the photoresist layer includes not only a photoresist material but also an electron beam resist material. There is no restriction | limiting in particular as said photoresist material, It can select suitably from well-known materials in the semiconductor field | area etc., For example, the material etc. which can utilize near ultraviolet light, near-field light, etc. are mentioned.

The pitch of the nanoholes is appropriately determined depending on the voltage in the anodizing treatment, and is approximately 2.5 times (nm) of the anodizing voltage (V). Therefore, the voltage in the anodizing treatment is not particularly limited, but is preferably 3 to 40 V, and more preferably 3 to 10 V, for example.
When the voltage is 3 to 40 V, the recording medium can be densified. When the voltage is 3 to 10 V, the pitch of the nanoholes can be 7 to 25 nm. This is particularly advantageous in that the density of the medium can be further increased.
In addition, there is no restriction | limiting in particular as a kind, density | concentration, temperature, time, etc. of the electrolyte solution in the said anodizing process, According to the number of nanoholes to form, a magnitude | size, an aspect-ratio, etc., it can select suitably. For example, preferable examples of the electrolyte include a diluted phosphoric acid solution, a diluted oxalic acid solution, and a diluted sulfuric acid solution. In any case, the adjustment of the aspect ratio of the nanohole can be performed by increasing the diameter of the nanohole (alumina pore) by immersing in a phosphoric acid solution after the anodizing treatment.

  There is no particular limitation on the method for enlarging the bottom hole diameter of the nanohole. For example, anodization of the nanohole region 1 (first region) and the nanohole region 2 (second region) is performed using acid solutions having different alumina solubility (for example, , Phosphoric acid and sulfuric acid) and separately at different temperatures. This is because nanoholes having different pore diameters can be formed by different alumina solubility. Furthermore, if only the aluminum film portion corresponding to the nanohole region 1 is alloyed with a metal such as Ti, Hf, Zr, Si, W, Ta, Nb, Mo, Cr, or Mg, the diameter of the nanohole region 1 is reduced. It is possible. Thereby, even if the hole diameter of the nanohole area | region 2 is fully expanded in the hole diameter expansion process using a suitable acid solution after that, it is possible to keep the hole diameter of the nanohole area | region 1 comparatively small. Since alumina can be made difficult to dissolve in acid by an appropriate heat treatment, heat treatment is performed after the formation of the nanohole region 1, and then the nanohole region 2 is formed, and a pore size expansion process is performed using an appropriate acid solution. It is possible to enlarge only the hole diameter of the nanohole region 2 by applying.

  The nanohole structure of the present invention can be suitably used in various fields such as a magnetic recording medium, a DNA chip, a catalyst substrate, and the like. It can be suitably used for a hard disk device or the like widely used as an external storage device or a consumer video recording device.

(Magnetic recording medium)
The magnetic recording medium of the present invention includes a substrate, a base material formed on the substrate, a nanohole having a predetermined depth from the surface of the base material, and having a diameter larger on the bottom side than on the surface side. There is no limitation other than having a hard magnetic material and a soft magnetic material filled in the nanohole, and further having other layers as necessary. That is, the magnetic recording medium of the present invention includes a substrate, the nanohole structure of the present invention, a hard magnetic material, and a soft magnetic material.

  The details of the substrate, the nanohole, and the nanohole structure are as described above.

The nanohole is preferably filled with a magnetic material to form a magnetic layer.
There is no restriction | limiting in particular as said magnetic layer, Although it can select suitably according to the objective, For example, a hard magnetic layer (ferromagnetic layer), a soft magnetic layer, etc. are mentioned. In the present invention, the hard magnetic layer and the soft magnetic layer are formed inside the nanohole. Further, a nonmagnetic layer (intermediate layer) may be formed between the hard magnetic layer and the soft magnetic layer.

The shape, structure, size, material and the like of the substrate are not particularly limited and can be appropriately selected according to the purpose. For example, the shape of the substrate is a magnetic disk such as a hard disk. In this case, the structure is a disk, and the structure may be a single layer structure or a laminated structure, and the material may be a base material of a magnetic recording medium. The material can be appropriately selected from known materials, and examples thereof include aluminum, glass, silicon, quartz, and SiO ₂ / Si formed by forming a thermal oxide film on the silicon surface. These board | substrate materials may be used individually by 1 type, and may use 2 or more types together.
In addition, the said board | substrate may be manufactured suitably and a commercial item may be used.

The hard magnetic layer functions as a recording layer in the magnetic recording medium and becomes a magnetic layer together with the soft magnetic layer.
The material of the hard magnetic layer is not particularly limited and can be appropriately selected from known materials according to the purpose. For example, Fe, Co, Ni, FeCo, FeNi, CoNi, CoNiP, FePt, CoPt And at least one selected from NiPt are preferred. These may be used individually by 1 type and may use 2 or more types together.
The hard magnetic layer, the not particularly limited as long as it is formed as a perpendicular magnetization film of a material, can be appropriately selected depending on the intended purpose, for example, a Ll ₀ ordered structure, wherein the C-axis substrate And those having an fcc structure or a bcc structure and having the C-axis aligned in the direction perpendicular to the substrate.

The thickness of the hard magnetic layer is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected according to the linear recording density used at the time of recording. For example, (1) the soft magnetism An aspect that is equal to or less than the thickness of the layer, (2) an aspect that is 1/3 to 3 times the minimum bit length determined by the linear recording density used during recording, and (3) the thickness of the soft magnetic layer and the underlayer The aspect which is below the total is preferable, for example, usually about 5 to 100 nm is preferable, 5 to 50 nm is more preferable, and when performing magnetic recording at a linear recording density of 1,500 kBPI targeting 1 Tb / in ² It is preferably 50 nm or less (about 20 nm).
Here, the thickness of the “hard magnetic layer” is such that the hard magnetic layer is a laminated structure or a structure divided into a plurality of layers (for example, a continuous layer divided by an intermediate layer such as a nonmagnetic layer). In other words, the total thickness of each hard magnetic layer is meant. Further, the thickness of the “soft magnetic layer” is such that the soft magnetic layer is a laminated structure or a structure divided into a plurality of layers (for example, a structure that is not divided into an intermediate layer such as a nonmagnetic layer to form a continuous layer). Means the total thickness of each soft magnetic layer. In addition, the “total thickness of the soft magnetic layer and the underlayer” refers to a structure in which at least one of the soft magnetic layer and the underlayer is divided into a laminated structure or a plurality of layers (for example, a nonmagnetic layer or the like). In the case of having a structure that is divided by the intermediate layer and is not a continuous layer, it means the total thickness of each soft magnetic layer and the underlayer.

In the case of a magnetic recording medium having the hard magnetic layer and the soft magnetic layer, the distance between the single magnetic pole head used for magnetic recording and the soft magnetic layer is the thickness of the nanohole structure (porous layer). And the thickness of the hard magnetic layer can be made substantially equal to the thickness of the hard magnetic layer, so that the magnetic flux from the single-pole head can be obtained only by the thickness of the hard magnetic layer regardless of the thickness of the nanohole structure (porous layer). It is possible to control the optimum magnetic recording / reproducing characteristics at the recording density used for concentration. As a result, in the magnetic recording medium, compared with the conventional magnetic recording medium, the writing efficiency is greatly improved, the writing current is reduced, and the overwrite characteristic can be remarkably improved.
The formation of the hard magnetic layer is not particularly limited and can be performed according to a known method, for example, an electroplating method or the like.
Specifically, after the nanohole structure is immersed in a plating solution, a voltage is applied using the electrode layer as an electrode to deposit or deposit the magnetic material.

  The soft magnetic layer is not particularly limited and can be appropriately selected from known materials according to the purpose. For example, at least one selected from Ni, NiFe, FeSiAl, FeC, FeCoB, FeCoNiB, and CoZrNb can be selected. Preferred examples include seeds. These may be used individually by 1 type and may use 2 or more types together.

  The thickness of the soft magnetic layer is not particularly limited as long as the effect of the present invention is not impaired, and is appropriately selected according to the depth of the nanohole in the nanohole structure (porous layer), the thickness of the ferromagnetic layer, and the like. For example, there are (1) an aspect in which the thickness of the ferromagnetic layer exceeds the thickness, and (2) an aspect in which the sum of the thickness of the base layer exceeds the thickness of the ferromagnetic layer.

The soft magnetic layer is advantageous in that the magnetic flux from the magnetic head used for magnetic recording can be effectively converged on the ferromagnetic layer, and the perpendicular component of the magnetic field of the magnetic head can be increased. . The soft magnetic layer is preferably capable of forming a magnetic circuit of a recording magnetic field input from the magnetic head together with the magnetic head together with an underlayer.
The soft magnetic layer preferably has an easy magnetization axis in a direction substantially perpendicular to the substrate surface. In this case, when recording is performed with the perpendicular magnetic recording head, the concentration of magnetic flux from the perpendicular magnetic recording head, the optimum magnetic recording / reproducing characteristics at the recording density to be used, and the like can be controlled. As a result of concentrating on the layers, the write efficiency is greatly improved, the write current is reduced, and the overwrite characteristics are remarkably improved as compared with the conventional magnetic recording apparatus.
The formation of the soft magnetic layer is not particularly limited and can be performed according to a known method, for example, an electroplating method or the like.
Specifically, after the nanohole structure is immersed in a plating solution, a voltage is applied using the electrode layer as an electrode, whereby the soft magnetic material is deposited or deposited.

The nanohole in the nanohole structure (porous layer) may have a nonmagnetic layer (intermediate layer) between the ferromagnetic layer and the soft magnetic layer. If the non-magnetic layer (intermediate layer) is present, the effect of the exchange coupling force between the ferromagnetic layer and the soft magnetic layer is weakened. Can be controlled to a desired reproduction characteristic.
The material of the nonmagnetic layer is not particularly limited and can be appropriately selected from known materials. For example, the material is selected from Cu, Al, Cr, Pt, W, Nb, Ru, Ta, and Ti. At least one of them. These may be used individually by 1 type and may use 2 or more types together.

There is no restriction | limiting in particular as thickness of the said nonmagnetic layer, According to the objective, it can select suitably.
The formation of the nonmagnetic layer is not particularly limited and can be performed according to a known method. For example, it can be performed by electrodeposition (electrodeposition method) or the like.

In the magnetic recording medium of the present invention, an underlayer may be provided between the substrate and the nanohole structure (porous layer).
The material for the underlayer is not particularly limited and can be appropriately selected from known materials. For example, the adhesion to the substrate and the adhesion to the nanohole structure (porous layer) Suitable materials and those described above as materials for the soft magnetic layer are preferable. These materials may be used individually by 1 type, may use 2 or more types together, and may mutually be the same as the material of the said soft-magnetic layer, and may differ.

The underlayer preferably has an easy axis of magnetization in the in-plane direction of the substrate surface. In this case, a magnetic circuit in which the magnetic flux from the magnetic head used for magnetic recording is effectively closed can be formed, and the vertical component of the magnetic field of the magnetic head can be increased. The underlayer is also effective in single domain recording with a bit size (opening diameter of the nanohole) of 100 nm or less.
The formation of the underlayer is not particularly limited and can be performed according to a known method. For example, it can be performed by electrodeposition (electrodeposition method), electroless plating, or the like.

  There is no restriction | limiting in particular as said other layer, Although it can select suitably according to the objective, For example, an electrode layer, a protective layer, a lubricant layer, etc. are mentioned.

The electrode layer is a layer that functions as an electrode when the magnetic layer (the ferromagnetic layer and the soft magnetic layer) is formed by electrodeposition or the like, and is generally on the substrate and below the ferromagnetic layer. Provided. In addition, when forming the said magnetic layer by electrodeposition, although this electrode layer may be used as an electrode, you may use the said base layer etc. as an electrode.
There is no restriction | limiting in particular as a material of the said electrode layer, According to the objective, it can select suitably, For example, Cr, Co, Pt, Cu, Ir, Rh, these alloys, etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together. The electrode layer may further contain W, Nb, Ti, Ta, Si, O, etc. in addition to these materials.

There is no restriction | limiting in particular as thickness of the said electrode layer, According to the objective, it can select suitably. One electrode layer may be provided, or two or more electrode layers may be provided.
The formation of the electrode layer is not particularly limited and can be performed according to a known method. For example, the electrode layer can be formed by a sputtering method, a vapor deposition method, or the like.

The protective layer is a layer having a function of protecting the ferromagnetic layer, and is provided on the surface or above the ferromagnetic layer. The protective layer may be provided in only one layer, may be provided in two or more layers, may have a single layer structure, or may have a laminated structure.
There is no restriction | limiting in particular as a material of the said protective layer, According to the objective, it can select suitably, For example, DLC (diamond-like carbon) etc. are mentioned.

There is no restriction | limiting in particular as thickness of the said protective layer, According to the objective, it can select suitably.
The formation of the protective layer is not particularly limited, and can be performed according to a known method according to the purpose. For example, it can be performed by a plasma CVD method, a coating method, or the like.

The magnetic recording medium of the present invention can be used for various types of magnetic recording using a magnetic head, but can be suitably used for magnetic recording using a single pole head. It can be particularly suitably used for the recording method.
The magnetic recording medium of the present invention is capable of high-density recording and high-speed recording without increasing the write current of the magnetic head, has a large capacity, has excellent overwrite characteristics, uniform characteristics, and high quality. For this reason, the magnetic recording medium can be designed and used as various magnetic recording media. For example, the magnetic recording medium is designed for a hard disk device widely used as an external storage device of a computer, a consumer video recording device, or the like. It can be used, and can be particularly suitably designed and used for a magnetic disk such as a hard disk.

-Manufacturing method of magnetic recording medium-
The method for producing the magnetic recording medium is a method for producing the magnetic recording medium of the present invention, and includes at least a nanohole structure forming step (porous layer forming step) and a magnetic material filling step, and further if necessary. It includes other processes such as a base layer forming process, an electrode layer forming process, a nonmagnetic layer forming process, and a polishing process, which are appropriately selected.

--- Underlayer formation process--
The base layer forming step is a step of selecting a base layer as necessary and forming a base layer on the substrate.
Examples of the substrate include those described above.
The underlayer can be formed according to a known method. For example, the underlayer may be formed by a sputtering method (sputtering), a vacuum film formation method such as a vapor deposition method, or electrodeposition (electrodeposition method). Alternatively, it may be formed by electroless plating.
The foundation layer having a desired thickness is formed on the substrate by the foundation layer forming step.

--- Electrode layer formation process--
The electrode layer forming step is a step of forming an electrode layer between the nanohole structure and the base layer.
The electrode layer can be formed according to a known method, but can be suitably performed by, for example, a sputtering method (sputtering) or a vapor deposition method. There is no restriction | limiting in particular as formation conditions of this electrode layer, According to the objective, it can select suitably.
The electrode layer formed in the electrode layer forming step is used as an electrode when forming at least one of a soft magnetic layer, a nonmagnetic layer, and a ferromagnetic layer by electrodeposition.

-Nanohole structure formation process (porous layer formation process)-
In the nanohole structure forming step (porous layer forming step), a nanohole structure (porous layer) is formed on a substrate (on the base layer when the base layer is formed by the base layer forming step). After forming a metal layer made of a metal material to be formed, a plurality of nanohole array pairs are formed in a direction substantially orthogonal to the substrate surface by forming grooves and lands in the metal layer and performing anodizing treatment. And forming a nanohole structure (porous layer). The method for forming the nanohole structure is as described above.
The nanohole structure (porous layer) is formed on the substrate or the base layer by the nanohole structure forming step (porous layer forming step).
Further, since the shape of the nanohole is substantially equal to the shape of the magnetic material to be filled, the nanohole shape is preferably matched with a desired magnetic material structure.

--- Magnetic material filling process ---
The magnetic material filling step is a step of filling a magnetic material into the nanohole formed in the nanohole structure (porous layer), and a hard magnetic layer forming step of filling the nanohole with the hard magnetic material, Including a soft magnetic layer forming step of filling the nanohole with the soft magnetic material.

--- Soft magnetic layer formation process ---
The soft magnetic layer forming step is a step of forming a soft magnetic layer inside the nanohole.
The soft magnetic layer can be formed by depositing or filling the above-described soft magnetic layer material into the nanoholes by electrodeposition or the like.
The electrodeposition method, conditions, etc. are not particularly limited and can be appropriately selected according to the purpose. For example, a solution containing the soft magnetic layer material using the underlayer or the electrode layer as an electrode. A method of depositing or depositing on the electrode by applying one or more kinds and applying a voltage is preferable.
By the soft magnetic layer forming step, the soft magnetic layer is formed inside the nanohole in the porous layer and on the substrate, the base layer, or the electrode layer.

--- Hard magnetic layer formation process ---
The hard magnetic layer forming step is a step of forming a hard magnetic layer on the soft magnetic layer (or on the nonmagnetic layer when the nonmagnetic layer is formed on the soft magnetic layer).
The hard magnetic layer can be formed by depositing or filling the above-described hard magnetic layer material on the soft magnetic layer formed inside the nanoholes by electrodeposition or the like.
The electrodeposition method, conditions, etc. are not particularly limited and may be appropriately selected depending on the purpose. For example, a solution containing the hard magnetic layer material using the underlayer or the electrode layer as an electrode. A method of depositing or depositing in the nanoholes by using one or two or more and applying a voltage is preferable.
By the hard magnetic layer forming step, the hard magnetic layer is formed inside the nanohole in the porous layer and on the soft magnetic layer or the nonmagnetic layer.

--Nonmagnetic layer formation process--
The nonmagnetic layer forming step is a step of forming a nonmagnetic layer on the soft magnetic layer.
The nonmagnetic layer can be formed by depositing or filling the above-described nonmagnetic layer material on the soft magnetic layer formed inside the nanohole by electrodeposition or the like.
The electrodeposition method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. For example, a solution containing the material of the nonmagnetic layer using the underlayer or the electrode layer as an electrode. A method of depositing or depositing in nanoholes by applying one or more types and applying a voltage is preferable.
By the nonmagnetic layer forming step, the nonmagnetic layer is formed inside the nanohole in the porous layer and on the soft magnetic layer or the like.

-Polishing process (surface treatment process)-
The polishing step is a step of polishing and planarizing the surface of the nanohole structure (porous layer) after the magnetic layer forming step (including the hard magnetic layer forming step and the soft magnetic layer forming step). is there.
There is no restriction | limiting in particular as the grinding | polishing method in the said grinding | polishing process, It can carry out according to a well-known method, For example, CMP process etc. are mentioned. When the surface of the magnetic recording medium is smoothed by the polishing step, a magnetic head such as a perpendicular magnetic recording head can be stably levitated, and both high density recording and low reliability can be achieved by low levitating. This is advantageous in that
Further, after the polishing treatment, it is preferable to form a carbon layer as a protective film by sputtering or the like, and to apply a lubricant.

  According to the method for manufacturing the magnetic recording medium, the magnetic recording medium of the present invention can be manufactured efficiently and at low cost.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
-Production of nanohole structures and production of magnetic recording media-

--- Underlayer formation process--
A 10 nm Ta layer, a CoZrNb25 nm / Ru0.6 nm / CoZrNb25 nm layer (so-called APS-SUL layer), a 10 nm Ta layer, on a hard disk (1 inch diameter) glass disk substrate by sputtering. A base layer having

-Nanohole structure formation process (porous layer formation process)-
On the underlayer formed in the underlayer forming step, an aluminum layer was formed by forming a film of Al with a thickness of 70 nm using a sputtering method.
Next, desired Al surface pattern formation for nanohole arrangement was performed using a nanoimprint lithography method (H. Oshima et al. Appl. Phys. Lett. 91,022508 (2007)).
Next, in the 0.3 M phosphoric acid solution at 0 ° C., the first anodizing treatment was performed at 6 V to form nanoholes (nanohole region 1) having a pore diameter of 5 nmφ, a depth of 25 nm, and a spacing of 25 nm on the entire surface of the disk. .
Next, a second anodizing treatment is performed at 6 V in a 0.3 M sulfuric acid aqueous solution at 20 ° C., and the bottom portion (substrate side) of the nanohole (nanohole region 1) formed by the first anodizing treatment is As side nanoholes, nanoholes (nanohole region 2) having a hole diameter of 10 nmφ, a depth of 40 nm, and an interval of 25 nm were formed on the entire surface of the disk.
Thus, a nanohole structure having a nanohole region 1 on the surface side with a pore diameter of 5 nmφ and a depth of 25 nm and a nanohole region 2 on the bottom side with a pore size of 10 nmφ and a depth of 40 nm as shown in FIG. 2 was formed.

--- Magnetic material filling process ---
In the magnetic material filling step, desired magnetic nanopillars were included in the nanoholes formed in the nanohole structure forming step (FIG. 4). First, the nanohole region 2 was filled with a NiFe alloy (soft magnetic material) by dipping in a plating solution for NiFe alloy and performing electroplating. The aspect ratio (depth 21 / diameter 31) of the NiFe alloy region was sufficiently small as 4, and the soft magnetic characteristics of the NiFe alloy region were maintained.
Next, the nanohole region 1 was filled with Co by immersing it in a plating solution for cobalt (Co) to perform electroplating. The aspect ratio (depth 20 / diameter 30) of the Co region was 5, and the perpendicular anisotropy of the Co region was realized.

(Example 2)
-Production of nanohole structures and production of magnetic recording media-

--- Underlayer formation process--
A 10 nm Ta layer, a CoZrNb25 nm / Ru0.6 nm / CoZrNb25 nm layer (so-called APS-SUL layer), a 10 nm Ta layer, on a hard disk (1 inch diameter) glass disk substrate by sputtering. A base layer having

-Nanohole structure formation process (porous layer formation process)-
On the underlayer formed in the underlayer forming step, an aluminum layer was formed by forming a film of Al with a thickness of 70 nm using a sputtering method.
Next, desired Al surface pattern formation for nanohole arrangement was performed using a nanoimprint lithography method (H. Oshima et al. Appl. Phys. Lett. 91,022508 (2007)).
Next, in the 0.3 M phosphoric acid solution at 0 ° C., the first anodizing treatment was performed at 6 V to form nanoholes (nanohole region 1) having a pore diameter of 5 nmφ, a depth of 25 nm, and a spacing of 25 nm on the entire surface of the disk. .
Next, the anodized alumina portion (layer 10) in which the nanohole region 1 is formed is heat-treated at 500 ° C., so that the anodized alumina portion (layer 10) in which the nanohole region 1 is formed is insoluble in acid. It was.
Next, a second anodizing treatment is performed at 6 V in a 0.3 M phosphoric acid aqueous solution at 0 ° C., and a bottom-side nanohole is formed on the bottom side (substrate side) of the nanohole region 1 formed by the first anodizing treatment. As a result, nanoholes (nanohole region 2) having a hole diameter of 5 nmφ, a depth of 40 nm, and an interval of 25 nm were formed on the entire surface of the disk.
Next, the pore diameter of the nanohole region 2 was widened to 10 nmφ by immersing in a phosphoric acid solution at 35 ° C. and 5 wt% to perform a pore diameter enlargement process.
Thus, a nanohole structure having a nanohole region 1 on the surface side with a pore diameter of 5 nmφ and a depth of 25 nm and a nanohole region 2 on the bottom side with a pore size of 10 nmφ and a depth of 40 nm as shown in FIG. 2 was formed.

--- Magnetic material filling process ---
In the magnetic material filling step, desired magnetic nanopillars were included in the nanoholes formed in the nanohole structure forming step (FIG. 4). First, the nanohole region 2 was filled with a NiFe alloy (soft magnetic material) by dipping in a plating solution for NiFe alloy and performing electroplating. The aspect ratio (depth 21 / diameter 31) of the NiFe alloy region was sufficiently small as 4, and the soft magnetic characteristics of the NiFe alloy region were maintained.
Next, the nanohole region 1 was filled with CoPt by being immersed in a CoPt plating solution and performing electroplating. Further, the CoPt region was heat-treated at 400 ° C. in a hydrogen atmosphere. By the heat treatment, magnetocrystalline anisotropy (perpendicular magnetic anisotropy) was developed in the CoPt region.

(Example 3)
-Production of nanohole structures and production of magnetic recording media-

--- Underlayer formation process--
A 10 nm Ta layer, a CoZrNb25 nm / Ru0.6 nm / CoZrNb25 nm layer (so-called APS-SUL layer), a 10 nm Ta layer, on a hard disk (1 inch diameter) glass disk substrate by sputtering. A base layer having

-Nanohole structure formation process (porous layer formation process)-
On the underlayer formed in the underlayer forming step, an aluminum layer was formed by forming a film of Al with a thickness of 70 nm using a sputtering method.
Next, desired Al surface pattern formation for nanohole arrangement was performed using a nanoimprint lithography method (H. Oshima et al. Appl. Phys. Lett. 91,022508 (2007)).
Next, in a 0.3 M sulfuric acid solution at 15 ° C., a first anodizing treatment was performed at 6 V to form nanoholes (nanohole region 1) having a pore diameter of 8 nmφ, a depth of 25 nm, and an interval of 25 nm on the entire surface of the disk. .
Next, a second anodizing treatment is performed at 6 V in a 2.0 M sulfuric acid aqueous solution at 35 ° C., and a bottom-side nanohole is formed on the bottom side (substrate side) of the nanohole region 1 formed by the first anodizing treatment. As a result, nanoholes (nanohole region 2) having a hole diameter of 12 nmφ, a depth of 40 nm, and an interval of 25 nm were formed on the entire surface of the disk.
As a result, a nanohole structure having a nanohole region 1 on the surface side with a pore diameter of 8 nmφ and a depth of 25 nm and a nanohole region 2 on the bottom side with a pore size of 12 nmφ and a depth of 40 nm as shown in FIG. 2 was formed.

--- Magnetic material filling process ---
In the magnetic material filling step, desired magnetic nanopillars were included in the nanoholes formed in the nanohole structure forming step (FIG. 4). First, the nanohole region 2 was filled with a NiFe alloy (soft magnetic material) by dipping in a plating solution for NiFe alloy and performing electroplating. The aspect ratio (depth 21 / diameter 31) of the NiFe alloy region was sufficiently small as 3.3, and the soft magnetic characteristics of the NiFe alloy region were maintained.
Next, the nanohole region 1 was filled with Co by immersing it in a plating solution for cobalt (Co) to perform electroplating.

(Experimental example 1)
FIG. 5 is a graph showing a simulation result of the magnetization curve in the depth (perpendicular) direction of the soft magnetic material (NiFe) -filled nanohole. However, (a) in FIG. 5 shows a magnetization curve of a soft magnetic (NiFe) filled nanohole having a diameter of 10 nm, a pitch of 30 nm, and a depth of 50 nm, that is, an aspect ratio of 5, and FIG. Shows a magnetization curve of soft magnetic material (NiFe) -filled nanoholes having a diameter of 10 nm, a pitch of 30 nm, and a depth of 30 nm, that is, an aspect ratio of 3.
In FIG. 5, in the nanohole (a) having an aspect ratio of 5 (depth 50 nm), the coercive force has increased to about 500 Oe due to the shape magnetic anisotropy. This indicates that it is difficult to function as a soft magnetic backing layer. On the other hand, in the nanohole (b) having an aspect ratio of 3 (depth 30 nm), coercive force is not generated and soft magnetism is maintained.
From the above, it can be understood that the aspect ratio of the filled soft magnetic material is smaller than 5 in order for the soft magnetic material filled in the nanohole to function as a soft magnetic backing layer.
Note that the aspect ratio dependence of the shape magnetic anisotropy when cobalt (Co) is filled is H.264. Kikuchi et al. IEEE Trans. Magn. 41 3226 (2005), and similar results (need less than 5) have been obtained.

(Experimental example 2)
FIG. 6 is a graph showing a simulation result of the recording magnetic field distribution in the cross track direction. However, (a) in FIG. 6 shows the result in the case of a soft magnetic backing layer (FIG. 7) of a continuous film (the soft magnetic backing layer is not separated), and (b) in FIG. The results when the backing layer is filled in the nanoholes (the soft magnetic backing layer is separated) are shown. Further, three rectangles indicated by dotted lines indicate the positions of the recording dots in the recording track and the adjacent track, and the reversal magnetic field strength of the recording dots.
In FIG. 6, in the case of the soft magnetic backing layer (FIG. 7) of (a), since the backing layer spreads over the entire surface, the magnetic field strength is large and the distribution in the cross track direction is wide. Further, the magnetic field in the adjacent track almost reaches the reversal magnetic field of the recording dots, and a writing error occurs in the adjacent track. On the other hand, when the soft magnetic underlayer of (b) is filled in the nanohole, the magnetic field strength is lower than that of the continuous film of (a), but a strength sufficiently higher than the reversal magnetic field is obtained. Further, the distribution in the cross track direction is narrow, and the magnetic field strength in the adjacent track is about half of the switching magnetic field. Therefore, no write error occurs.
As described above, the soft magnetic material is filled in the nanoholes to function as a soft magnetic backing layer ((b) in FIG. 6), so that the recording magnetic field is more effective than in the case of the continuous film backing layer ((a) in FIG. 6). You can see that you can concentrate.

  From Experimental Examples 1 and 2, it was found that the soft magnetic underlayer was filled in the nanoholes, and that the aspect ratio of the nanoholes filled in the soft magnetic underlayer was required to be smaller than 5.

The preferred embodiments of the present invention are as follows.
(Supplementary note 1) A nanohole structure comprising: a base material; and a nanohole having a predetermined depth from the surface of the base material and having a diameter larger on the bottom side than on the surface side.
(Supplementary Note 2) The nanohole has a first region having a first length from the surface of the base material, and has a diameter larger than the first region on the bottom side from the first region, The nanohole structure according to supplementary note 1, including a second region having a length of two.
(Supplementary note 3) The nanohole structure according to supplementary note 2, wherein a sum of the first length and the second length is equal to the predetermined depth.
(Supplementary note 4) The nanohole structure according to supplementary note 2 or 3, wherein the first region is filled with a hard magnetic material, and the second region is filled with a soft magnetic material.
(Supplementary note 5) The nanohole structure according to any one of supplementary notes 2 to 4, wherein a ratio (second length / diameter) of the second length to the diameter in the second region is 5 or less.
(Supplementary note 6) The nanohole structure according to any one of supplementary notes 2 to 5, wherein the diameter in the second region is 1.25 times or more the diameter in the first region.
(Supplementary note 7) A substrate, a base material formed on the substrate, a nanohole having a predetermined depth from the surface of the base material and having a larger diameter on the bottom side than the surface side, and the nanohole A magnetic recording medium comprising a hard magnetic material and a soft magnetic material filled therein.
(Supplementary Note 8) The nanohole has a first region having a first length from the surface of the base material, and has a diameter larger than that of the first region on the bottom side from the first region and is second to the bottom. The magnetic recording medium according to appendix 7, including a second region having a length of.
(Supplementary note 9) The magnetic recording medium according to supplementary note 8, wherein the first region is filled with a hard magnetic material, and the second region is filled with a soft magnetic material.

The nanohole structure of the present invention can be suitably used in various fields such as a magnetic recording medium, a DNA chip, a diagnostic device, a detection sensor, a catalyst substrate, a field emission display, and in particular, an external storage device of a computer, It can be suitably used for a hard disk device or the like widely used as a consumer video recording device or the like.
The magnetic recording medium of the present invention can be suitably used for hard disk drives and the like that are widely used as external storage devices for computers, consumer video recording devices, and the like.

FIG. 1 is a view of a part of the nanohole array as viewed from above, and is an explanatory diagram of the pitch and diameter of the nanoholes. FIG. 2 is a schematic explanatory view showing the magnetic recording medium of the present invention (No. 1). FIG. 3 is a schematic explanatory view showing the structure of the nanohole in the nanohole structure of the present invention. FIG. 4 is a schematic explanatory view showing the magnetic recording medium of the present invention (part 2). FIG. 5 is a graph showing a simulation result of the magnetization curve in the depth (perpendicular) direction of the soft magnetic material (NiFe) -filled nanohole. FIG. 6 is a graph showing a simulation result of the recording magnetic field distribution in the cross track direction. FIG. 7 is a schematic explanatory view showing a conventional nanohole structure (No. 1). FIG. 8 is a schematic explanatory view showing a conventional nanohole structure (part 2).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nanohole area | region 2 Nanohole area | region 10 Layer 11 Layer 20 Depth 21 Depth 30 Hole diameter 31 Hole diameter

Claims (9)

A substrate;
A nanohole having a predetermined depth from the surface of the substrate, and having a larger diameter on the bottom side than on the surface side;
Nanohole structure characterized by having.   The nanohole has a first region having a first length from the surface of the base material, and has a diameter larger than the first region on the bottom side from the first region, and has a second length to the bottom. The nanohole structure according to claim 1, comprising a second region having   The nanohole structure according to claim 2, wherein a sum of the first length and the second length is equal to the predetermined depth.   The nanohole structure according to claim 2 or 3, wherein the first region is filled with a hard magnetic material, and the second region is filled with a soft magnetic material.   The nanohole structure according to any one of claims 2 to 4, wherein a ratio (second length / diameter) of the second length to the diameter in the second region is 5 or less.   The nanohole structure according to any one of claims 2 to 5, wherein a diameter in the second region is 1.25 times or more of a diameter in the first region. A substrate,
A base material formed on the substrate;
A nanohole having a predetermined depth from the surface of the substrate, and having a larger diameter on the bottom side than on the surface side;
A hard magnetic material and a soft magnetic material filled in the nanohole,
A magnetic recording medium comprising:   The nanohole has a first region having a first length from the surface of the base material, and has a diameter larger than the first region on the bottom side from the first region and a second length to the bottom. The magnetic recording medium according to claim 7, further comprising a second region having the second region.   The magnetic recording medium according to claim 8, wherein the first region is filled with a hard magnetic material, and the second region is filled with a soft magnetic material.