JP4027151B2 - Method for manufacturing magnetic recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a magnetic recording medium.Manufacturing methodIn particular, a magnetic recording medium that enables high-density recording by realizing multi-level recordingManufacturing methodAbout.
[0002]
[Prior art]
With the rapid progress of information processing in recent years, the recording density of an information recording apparatus using a magnetic recording medium represented by a hard disk continues to increase at an annual rate of 60 to 100%. In the future, the amount of information recording is expected to increase, and further higher density is required.
[0003]
At present, as a method of magnetic recording on a hard disk, a longitudinal recording method in which magnetization is recorded in a direction horizontal to the substrate, a so-called in-plane recording method is employed. In the in-plane recording method, recording / reproduction is performed by a magnetic head using a leakage magnetic field from a magnetization transition region provided between adjacent magnetization recording portions. However, in the in-plane recording method, the leakage magnetic field decreases due to the influence of the demagnetizing field in the magnetic domain as the density increases, so that the magnetic recording layer must be made thinner. As a result, the volume per magnetic fine particle becomes extremely small, resulting in a superparamagnetic state in which the magnetization direction changes due to the influence of thermal energy, and the recorded magnetization cannot be maintained. For the reasons as described above, the in-plane recording method is 100 Gb / in.² The recording density before and after is considered to be the limit.
[0004]
On the other hand, 100Gb / in² In the recording density region exceeding 1, the perpendicular magnetic recording method in which the magnetic layer having magnetic anisotropy in the direction perpendicular to the substrate is used as the recording layer and magnetization is recorded in the direction perpendicular to the substrate is promising. Research to shift to the method is being conducted energetically. In contrast to the in-plane recording system, the perpendicular magnetic recording system has a property that the demagnetizing field decreases as the density increases. In addition, since it is possible to increase the thickness of the magnetic layer even if the recording density is increased, it is superior to the in-plane recording method over the superparamagnetic state due to the influence of thermal energy.
[0005]
In the perpendicular magnetic recording system, a Co—Cr alloy is generally used as a recording layer. When a Co—Cr alloy film is formed by sputtering on a substrate such as a Si substrate, a glass substrate, or a carbon substrate, Co and Cr grow in a state where the composition is separated. Of these, the portion with a large Co composition is columnar, becomes a ferromagnetic portion having a hexagonal close-packed structure (hcp structure), and becomes a recording portion. The portion having a large Cr composition that grows so as to surround the columnar recording portion is a nonmagnetic portion, and also serves to weaken the magnetic interaction between adjacent recording portions.
[0006]
Furthermore, as a next-generation recording technology, a structure in which a magnetic material to be a columnar recording portion as described above is embedded in a non-magnetic material is regularly manufactured by a microfabrication technology, and binary values are obtained for a plurality of magnetic domains. Discrete media for recording or patterned media for recording binary values for one magnetic domain have been proposed.
[0007]
Since the perpendicular magnetic recording method uses a Co—Cr segregation structure, the size and shape of the recording portion are not uniform, and it is difficult to place the recording portion in a desired pattern and position. Therefore, the bit boundary between the magnetic domains for recording binary values has an irregular shape, which causes a decrease in S / N.
[0008]
On the other hand, in discrete media and patterned media, magnetic domains of uniform size and shape are artificially arranged in a regular pattern, so that there is no problem as described above, and S / N reduction is suppressed. Therefore, it can be said that the structure is suitable for higher density recording.
[0009]
However, with the above-described discrete media and patterned media, it is expected that the difficulty of tracking between the media and the head and the difficulty of miniaturizing the head will increase as the density increases further. The Therefore, multi-level recording is effective as a method corresponding to higher density. Multi-level recording is for recording three or more values in a conventional binary recording area. For example, if four-value recording is performed, the recording density is doubled compared to the conventional one, and the recording density is increased with the same recording area. Is possible.
[0010]
A plurality of proposals have been made as a multi-level recording method. First, Japanese Patent Laid-Open No. 2000-298892 discloses a method of simultaneously detecting not only magnetic information of a recording layer but also a shape change of a magnetic material due to magnetism as a thermal asperity signal and performing multi-value recording by combining magnetic information and volume information. ing. However, the thermal asperity signal is generated when the magnetic head collides with the protrusion of the magnetic material whose shape has changed, making it difficult to track in a fine recording area and ensuring a sufficient media / magnetic head life. Is considered difficult.
[0011]
Japanese Patent Laid-Open No. 2000-52535 proposes a method in which magnetization is proportional to the strength of the applied magnetic field on a single recording layer, and linearly polarized light is irradiated on the recording layer to record multi-stage polarization plane rotation angles in multi-value information. Has been. In this method, it is considered difficult to maintain a plurality of magnetization states proportional to the applied magnetic field in the single recording layer for a sufficient time from the viewpoint of thermal demagnetization and the like.
[0012]
Further, Japanese Patent Laid-Open No. 6-52535 proposes a method of performing binary recording on one recording layer and performing multi-value recording by combining binary information of a plurality of recording layers as in the conventional recording method. This method has no contact between the medium and the magnetic head, and binary information is recorded in each layer, so it is conceptually strong against thermal demagnetization in a single magnetic recording area, but in the above proposal, An artificial lattice film extending in the in-plane direction is used, and magnetization reversal occurs due to the strong interaction between magnetic domains in the recording area and at the boundary, and appears as noise during reproduction. Moreover, it goes without saying that multi-level recording is more susceptible to noise if the dynamic range is the same as that in normal binary recording.
[0013]
Next, since the present invention uses anodized alumina nanoholes formed by anodization of Al, anodized alumina nanoholes will be described below.
[0014]
When an Al substrate is anodized in an acidic electrolyte such as sulfuric acid, oxalic acid, or phosphoric acid, an anodic oxide film that is a porous anodic oxide film is formed (for example, RC Furneaux, WR Rigby & A. et al. P. Davidson “NATURE” Vol.337, P147 (1989)). This porous film is characterized by a unique geometric structure in which extremely fine cylindrical pores (nanoholes) with a diameter of several nanometers to several hundred nanometers are arranged in parallel at intervals of several tens of nanometers to several hundred nanometers. It is in having. The cylindrical pores have a high aspect ratio and are excellent in depth and cross-sectional diameter uniformity.
[0015]
Further, the structure of the porous film can be controlled to some extent by changing the anodizing conditions. For example, it is known that the pore interval can be controlled to some extent by pore widening, and the pore diameter can be controlled to some extent by pore widening treatment. Here, the pore wide treatment is an etching treatment of alumina, and a wet etching treatment with ordinary phosphoric acid is used.
[0016]
Further, in order to improve the controllability of the pore shape, spacing and pattern of the porous film, a method of forming the pore formation start point using a stamper, that is, a substrate having a plurality of protrusions on the surface is made of Al. There has also been proposed a method of creating a porous film having pores exhibiting better shape, spacing and pattern controllability by forming an indentation formed on the surface of the substrate as a starting point of pore formation and then performing anodization. (Japanese Patent Laid-Open No. 10-121292 or Masuda “Solid Physics” 31,493 (1996)).
[0017]
[Problems to be solved by the invention]
  It is an object of the present invention to weaken the interaction between adjacent magnetic domains by using a magnetic cell in which a magnetic material is separated using a non-magnetic material as a partition, and to artificially create a plurality of types of magnetic domains of uniform size and shape. Magnetic recording medium capable of multi-level recording that overcomes the problems of conventional multi-level recording by arranging them in a regular patternManufacturing methodIs to provide.
[0018]
  Further, by forming a plurality of types of nanoholes having different depths or cross-sectional areas on the same substrate and selectively filling different types of magnetic materials with respect to the alumina nanoholes having different depths or cross-sectional areas, the coercive force is increased. Magnetic recording medium in which different magnetic cells are manufactured and multi-value recording is possible by combining the respective magnetic cellsManufacturing methodIs to provide.
[0019]
[Means for Solving the Problems]
  The problems of the conventional magnetic recording medium capable of multi-value recording are solved by the following configuration and manufacturing method according to the present invention.
  In the present invention, magnetic cells composed of magnetic material-filled pores separated from each other by a non-magnetic material are arranged on a substrate, and unit recording is performed on an area where a plurality of types of magnetic material cells having different coercive forces are present. Binary recording is performed on the same type of magnetic cell in the unit recording area, and multi-level recording of binary or more is performed in the unit recording area by combining each of the plurality of types of magnetic cells. A method of manufacturing a magnetic recording medium capable of performing an anodizing process comprising: forming an anodized film made of a metal containing Al as a main component on a substrate; anodizing the anodized film; Forming a plurality of types of pores having different shapes in a non-magnetic material comprising a film, and filling a plurality of types of pores having different shapes with different types of magnetic materials by changing the electrodeposition potential. A method of manufacturing a magnetic recording medium characterized by .
  The magnetic recording medium manufactured by the method of the present invention has the following characteristics.
[0021]
In the above magnetic recording medium, there is one magnetic cell of the same type existing in the unit recording area.
Alternatively, in the magnetic recording medium, the magnetic recording medium is characterized in that two or more magnetic cells of the same type exist in the unit recording area.
In the above magnetic recording medium, the coercive force of the magnetic cell is changed by changing the cross-sectional area of the pore.
[0022]
Alternatively, in the above magnetic recording medium, the coercive force of the magnetic cell is changed by filling different types of magnetic materials.
In the above magnetic recording medium, the pores are anodized alumina nanoholes formed by anodizing a metal containing Al as a main component.
Alternatively, in the above magnetic recording medium, the magnetic recording medium is characterized in that a plurality of kinds of magnetic cells having different coercive forces in the unit recording area are regularly arranged on the substrate.
[0024]
Further, in the above method for manufacturing a magnetic recording medium, a preferentially formed pore and a nonpreferentially formed pore are formed on the substrate by anodizing a metal mainly composed of Al. A method of manufacturing a magnetic recording medium, comprising the step of: The cross-sectional area of the pores formed preferentially is larger than the cross-sectional area of the non-preferentially formed pores.
[0025]
In the method for manufacturing a magnetic recording medium, the step of forming the pores may be performed by anodizing a plurality of types of recesses having different sizes in a metal film mainly composed of Al formed on a substrate. A method of manufacturing a magnetic recording medium, wherein a plurality of types of pores are formed.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0028]
<Configuration of magnetic recording medium>
A multi-value recordable magnetic recording medium according to the present invention will be described with reference to the drawings.
1A and 1B are schematic views showing an example of a magnetic recording medium according to the present invention. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line AA 'in FIG. In FIG. 1, the magnetic recording medium of the present invention has magnetic cells made up of pores filled with a magnetic material separated from each other by a non-magnetic material 12 on a substrate 11. There are two types of magnetic substance cell A13 and magnetic substance cell B14 having different cross-sectional areas of the pores. These two types of magnetic cells are magnetic cells having different coercive forces. In this configuration example, binary recording is performed using the two magnetic cells A13 included in the unit recording area 15, and binary recording is performed using the two magnetic cells B14. A total of four values can be recorded in the recording area 15.
[0029]
On the substrate, magnetic cells A13 and magnetic cells B14 having mutually different coercive forces are regularly and alternately arranged in a straight line. The unit recording area refers to an area including at least one of the two types of regularly arranged magnetic cells A13 and B14. The unit recording areas including the magnetic cell A13 and the magnetic cell B14 are also regularly arranged on the substrate. In FIG. 1, an area including two magnetic cells A and B is used as a unit recording area. However, the unit recording area is not limited to this, for example, the magnetic cell A and the magnetic cell B. May be one or three of each. Of course, there may be three or more. Further, the number of magnetic cells A and B included in the unit recording area may be different.
[0030]
FIG. 2 schematically shows each type of magnetic substance cell in the unit recording area 15 of FIG. 1 and the magnetization curve of the unit recording area 15. A combination of the magnetization curve 21 of the magnetic cell A13 and the magnetization curve 22 of the magnetic cell B14 is a magnetization curve 23 of the unit recording area 15. From the shape of the magnetization curve 23 of the unit recording area, H₁ , H₂ , -H₁ , -H₂ M for the applied magnetic field₁ , M₂ , -M₁ , -M₂ 4 values can be recorded.
[0031]
The configuration of the magnetic recording medium capable of multi-value recording in the present invention is not limited to that shown in FIG. 1, and two or more kinds of magnetic cells having different saturation magnetization and coercive force are provided in the unit recording area. You may have. That is, it is possible to perform multilevel recording of four or more values in the unit recording area. In FIG. 1, when the saturation magnetizations of the magnetic cell A13 and the magnetic cell B14 are equal, ternary recording is performed in the unit recording area.
[0032]
Further, the number of the same type of magnetic cells included in the unit recording area is not particularly limited as long as it is 1 or more, and the arrangement of the magnetic cells and the shape of the unit recording area are also the unit recording area. There is no particular limitation as long as it has an arrangement in which at least two types of magnetic cells having different coercive forces are included and can be recorded / reproduced by a magnetic head. The cross-sectional shape of the magnetic cell is not limited to a circle, and may be a rectangle or an ellipse.
[0033]
As a magnetic material of the magnetic cell, a perpendicular magnetic recording material that is magnetized perpendicularly to the substrate can be used, or an in-plane magnetic recording material that is magnetized parallel to the substrate can be used. However, when the aspect ratio of the magnetic cell becomes small, the tendency to magnetize in the plane becomes strong due to the influence of shape anisotropy. Therefore, when a perpendicular magnetic recording material is used, the aspect ratio is 0.5 or more. It is preferable. Here, the aspect ratio of the magnetic body cell is defined by x / y using the height (x) of the magnetic body cell and the longest diameter (y) in the cross-sectional shape of the magnetic body cell. For example, when the cross-sectional shape of the magnetic cell is circular, y is the diameter.
[0034]
As a method of changing the coercive force of the magnetic cell, there are a method of changing the cross-sectional area of the magnetic cell and a method of changing the magnetic material. For example, when perpendicular magnetic recording materials are used, if the height of the magnetic cell is the same, the magnetic cell with a higher aspect ratio has the same magnetic properties than the magnetic cell with a lower aspect ratio due to the influence of shape anisotropy. The coercive force is increased even with materials, and magnetic cells having different coercive forces can be produced. Also, magnetic cells having different coercive forces can be produced by magnetic cells made of magnetic materials having significantly different perpendicular magnetic anisotropy, such as CoPt magnetic cells and Co magnetic cells.
[0035]
As the nonmagnetic material 12 that separates the magnetic cells, resist, oxide, Cr, or the like can be used. In particular, the oxide is preferably alumina, and is preferably an alumite film formed by anodization of Al or anodized alumina.
[0036]
When Al is anodized, an alumite film 31 having nanoholes 36 having a structure as shown in FIG. 3 is formed. The nanohole diameter 32 can be in the range of several nanometers to several hundred nanometers, and the nanohole interval 33 can be controlled from a value slightly larger than the nanohole diameter 32 to about 500 nm. Various acids can be used for anodic oxidation, but a sulfuric acid bath is used to make nanoholes with fine spacing, a phosphoric acid bath is used to make nanoholes with relatively large spacing, and oxalic acid is used to make nanoholes between them. A bath is preferred. The diameter 32 of the nanohole can be enlarged by wet etching in a solution such as phosphoric acid.
[0037]
In order to fill a nanohole with a magnetic material to form a magnetic cell, a vacuum vapor deposition method or a sputtering method can be used, but an electrodeposition method is preferable from the viewpoint of filling a nanohole with a large aspect ratio.
[0038]
Any number of nanohole aspect ratios can be produced depending on the thickness of the anodized Al film and the anodizing conditions. However, when a perpendicular magnetic recording material is filled into nanoholes by electrodeposition to form a magnetic cell, Thus, it is desirable that the aspect ratio is 0.5 or more. In order to improve the controllability of electrodeposition and the crystallinity of the electrodeposition material, a conductive layer made of Cu, an alloy containing Cu as a main component, a noble metal or the like is provided between the substrate 34 and the anodized layer (Al film). It may be provided.
[0039]
As the anodized layer, Al is generally used, but other elements may be included as long as it can be anodized with a film containing Al as a main component. For the deposition of Al, a vacuum vapor deposition method by resistance heating, a sputtering method, a CVD method, or the like can be used as long as it can form a film having a flat surface to some extent.
[0040]
The surface of the magnetic recording medium is subjected to surface polishing using an abrasive such as diamond slurry and has flatness. m. s (root-mean-square) is 1 nm or less. In addition, in order to provide wear resistance to the magnetic head for recording / reproducing, a protective layer using carbon and a nonmagnetic material such as carbide or nitride may be provided on the surface.
[0041]
As the substrate 11, plastic, Si, glass, carbon, Ni-P plated Al, Si-C, or the like can be used.
[0042]
<Method of manufacturing magnetic recording medium>
An example of a method for manufacturing a magnetic recording medium in the present invention will be described. In particular, a case will be described in which a magnetic cell having different cross-sectional areas of pores (nanoholes) as shown in FIG. 1 is produced using anodized alumina as a nonmagnetic material for separating magnetic cells.
[0043]
4 and 5 are process diagrams showing an example of a method for manufacturing a magnetic recording medium according to the present invention. First, as shown in FIG. 4 (a), a conductive layer 42 made of Cu, an alloy containing Cu as a main component, or a noble metal as an electrode layer for electrodeposition is provided on a substrate 41 such as Si or glass. An anodized film 43 made of Al or a metal mainly composed of Al is provided thereon.
[0044]
Next, by using an electron beam exposure or the like, a convex stamper regularly arranged on a hard substrate such as SiC is pressed against the surface of the anodized film 43, etc. A recess 44 is formed as shown in FIG. At this time, the depression 44 is not formed in a place where the magnetic cell having a small cross-sectional area of the nanohole is to be arranged. Alternatively, in a place where a magnetic cell having a small cross-sectional area of nanoholes is to be arranged, a dent smaller than the dent 44 formed in a place where a magnetic cell having a large cross-sectional area of nanoholes is arranged is formed.
[0045]
Next, anodization is performed. In the anodic oxidation of Al or the like, nanoholes are formed preferentially from the portion where the depression is formed in the anodized film, and the nanohole is formed more slowly in the portion where the depression is not formed than in the portion where the depression is formed. The cross-sectional area and depth of the pore are smaller than those of the nanohole formed from the portion where the depression is formed. Therefore, the structure as shown in FIG. That is, with the alumina 45 as a partition, a nanohole A46 formed from the depression 44 with a large cross-sectional area and a nanohole B47 formed with a small cross-sectional area formed from a portion without the depression and a shallow depth are formed on the conductive layer 42. The
[0046]
Next, the magnetic material is filled into the nanoholes by electrodeposition. At this time, since the depth of the nanohole B47 is shallower than that of the nanohole A46, the thickness of the alumina 45 remaining at the bottom of the nanohole is thicker than that of the nanohole A46. Become. Therefore, first, low potential electrodeposition is performed, and as shown in FIG. 5D, only the nanohole A46 is selectively filled with the magnetic material A48.
[0047]
Further, a different kind of magnetic body B49 having a higher coercive force than the already filled magnetic body A48 is filled into the nanohole B47 by electrodeposition at a higher potential. Of course, since the nanohole A46 is also filled, electrodeposition is performed as shown in FIG.
Finally, the surface is subjected to surface polishing using an abrasive such as diamond slurry as shown in FIG. 5 (f).
[0048]
According to the above embodiment, magnetic cells having different coercive forces can be manufactured on the substrate. Further, the method for producing a multi-value recordable magnetic recording medium using anodized alumina in the present invention is not limited to the above production method. FIG. 6 is a process diagram showing another example of the method for producing a magnetic recording medium of the present invention. For example, the first electrodeposition is performed on the nanohole A51 as shown in FIG. 6A, and the nanohole A51 exists at the bottom of the nanohole B52 with an acid / alkali such as phosphoric acid or NaOH as shown in FIG. 6B. The bottom alumina 53 may be dissolved, and then the second electrodeposition may be performed to produce the structure shown in FIG. By dissolving the bottom alumina 53, the second electrodeposition potential can be set at a low potential as in the case of the first electrodeposition, so that the controllability of electrodeposition and the crystallinity of the electrodeposit can be improved. .
[0049]
In addition to using a stamper as described above in order to produce nanoholes formed preferentially and nanoholes formed non-preferentially, as shown in Japanese Patent Laid-Open No. 2001-9800, convergence is made. An ion beam (FIB) may be used. Alternatively, instead of forming a recess in the anodized film, a patterned resist layer 61 and the like is disposed on the anodized film 64 as shown in FIG. By oxidizing, it is possible to form nanoholes preferentially from the portion where the resist layer 61 does not exist on the anodized film. At this time, the resist layer 61 present on the anodized film is peeled off in an acidic bath during anodic oxidation, and then nanoholes are formed non-priorly from the portion where the resist layer 61 is peeled off.
[0050]
【Example】
  The present invention will be specifically described below with reference to examples.
  In the following examples, Examples 1 and 2 show reference examples of the present invention.
[0051]
Example 1
This example relates to the production of a magnetic cell having different coercive forces using anodized alumina.
FIG. 8 is a process diagram showing an embodiment of a method for manufacturing a magnetic recording medium according to the present invention. As shown in FIG. 8A, a film of Ti72 was formed on the Si substrate 71 to a thickness of 10 nm, Cu73 was formed to 20 nm, and Al74 was formed thereon to a thickness of 200 nm by sputtering. Subsequently, as shown in FIG. 8B, FIB was used on the Al surface to form a recess 75 serving as a starting point for forming nanoholes. In this embodiment, as shown in FIG. 9A, the depressions having a pattern arranged in a square shape so that the interval between adjacent depressions is 100 nm were formed. FIG. 9B is a cross-sectional view taken along the line BB ′ of FIG. At this time, by changing the FIB irradiation time to 10 msec and 30 msec so that the sizes of the adjacent depressions are different, the small depression 81 is large for the irradiation time of 10 msec and large for the irradiation time of 30 msec. A depression 82 was formed.
[0052]
Next, anodic oxidation was performed at an applied voltage of 40 V in a 0.3 mol / L oxalic acid bath at 16 ° C. A current profile during anodization is shown in FIG. The anodic oxidation was stopped 30 seconds after the current value began to decrease at the current value decrease start point and halved from the constant current value. Thereafter, the nanoholes thus formed are subjected to pore-wide treatment by being immersed in a 5 wt% phosphoric acid solution at 24 ° C. for 30 minutes. When the cross section of the prepared sample was observed with an FE-SEM (field emission scanning electron microscope), nanoholes corresponding to the pattern of the depressions were confirmed as shown in FIG. The cross-sectional shape of the formed nanohole was a circular shape in which the nanohole 76 formed from a large depression was about 70 nm in diameter and the nanohole 77 formed from a small depression was about 40 nm in diameter. It was also confirmed that the bottom alumina 78 was present in the nanoholes 77 formed from small depressions.
[0053]
Next, the magnetic material was electrodeposited onto the nanoholes. Co was selected as the magnetic material, and a mixed solution of cobalt (II) sulfate heptahydrate 0.2 mol / L and boric acid 0.3 mol / L was used at 24 ° C. for electrodeposition. Moreover, Ag / AgCl was used for the reference electrode. When the electrodeposition potential is −5.0 V, Co is filled even in the nanohole where the bottom alumina 78 remains, and the Co overflowing from the nanohole is surface-polished using a diamond slurry having a particle diameter of ¼ μm. As a result, the state shown in FIG.
[0054]
The magnetic characteristics of the prepared sample were measured using a VSM (sample vibration type magnetic force meter). FIG. 11 shows a magnetization curve perpendicular to the sample substrate. At this time, as shown in FIG. 11, Co filled in the nanohole 76 formed from the large depression and Co filled in the nanohole 77 formed from the small depression have different coercive forces of 1 kOe and 1.8 kOe, respectively. It was confirmed.
[0055]
Example 2
This example relates to MFM (magnetic force microscope) observation of the sample manufactured in Example 1.
First, a magnetic field of 3 kOe was applied to the sample manufactured in Example 1 in a direction perpendicular to the substrate to magnetize the magnetization of all the magnetic cells in the direction of the applied magnetic field. The MFM image at this time had a uniform contrast in all the magnetic cells. At this time, the magnetization state of the sample is the state shown in FIG.
[0056]
Subsequently, when the magnetic field of 1 kOe was applied in the opposite direction and the surface of the sample was observed with MFM, the contrast of the MFM image was reversed only for the nanoholes formed from the large depressions. That is, the magnetization state at this time is the state of FIG.
Next, when the applied magnetic field was changed from 1 kOe to 3 kOe, the contrast of the nanoholes formed from the small depressions was also reversed, and as a result, the contrast of the uniform MFM image was obtained. The magnetization state of the sample at this time is shown in FIG.
[0057]
Furthermore, when a magnetic field of 1 kOe was applied in the reverse direction, the contrast of the MFM image was reversed only for nanoholes formed from large depressions again, and the state shown in FIG.
Finally, when the applied magnetic field was changed from 1 kOe to 3 kOe, the state returned to the initial state of FIG.
That is, the four values shown in FIGS. 12A to 12D can be recorded by controlling the value of the applied magnetic field as in this embodiment.
[0058]
Example 3
This example relates to the production of a magnetic cell having different coercive forces using anodized alumina. In particular, it relates to fabricating a magnetic cell filled with different magnetic materials.
[0059]
FIG. 13 is a process diagram showing another embodiment of the method for manufacturing a magnetic recording medium according to the present invention. As in Example 1, after forming a Ti film on a Si substrate to a thickness of 10 nm, Cu to a thickness of 20 nm and Al to a thickness of 200 nm by sputtering, formation of the starting point by FIB, anodization, and pore-wide treatment were performed. It was.
[0060]
Next, Co was electrodeposited using a mixed solution of cobalt (II) sulfate heptahydrate 0.2 mol / L and boric acid 0.3 mol / L at 24 ° C. Ag / AgCl was used for the reference electrode. In this example, the electrodeposition potential was set to -1.0V. The electrodeposition was stopped before Co of the electrodeposit overflowed from the nanohole, and the cross section of the sample was observed with FE-SEM. As shown in FIG. 13A, only the nanohole 121 formed from a large depression was observed. Co filling was performed, and it was observed that no electrodeposition was performed on the nanoholes 123 formed from the small depressions where the bottom alumina 122 remained.
[0061]
Further, an aqueous solution composed of cobalt (II) sulfate heptahydrate 0.2 mol / L and boric acid 0.3 mol / L and hexachloroplatinic acid hexahydrate 0.1 mol / L mixed at a ratio of 1: 1. Was used for electrodeposition of CoPt. At this time, Ag / AgCl was used for the reference electrode, and the electrodeposition potential was -5.0V. After electrodeposition of CoPt, CoPt overflowing from the nanoholes was removed by surface polishing using a diamond slurry having a particle diameter of 1/4 μm, as in Example 1. Thereafter, the sample was annealed in a vacuum at 500 ° C. for 10 minutes, and the cross section of the sample was observed with FE-SEM. As shown in FIG. 13B, all nanoholes were filled with electrodeposits. It was in a state.
[0062]
Further, the magnetic properties of the sample produced in the same manner as in Example 1 were measured using a VSM (sample vibration type magnetic force meter). The magnetization curve in the direction perpendicular to the substrate had the shape shown in FIG. 11 as in Example 1. However, Co filled in the nanoholes 121 formed from large depressions and nanoholes formed from small depressions. The coercive force of CoPt filled in 123 was 1 kOe and 2.5 kOe, which was a large difference compared to Example 1.
[0063]
According to this embodiment, it is possible to manufacture a magnetic cell filled with different magnetic materials, and by filling magnetic materials having different coercive forces such as Co and CoPt, it is larger than the case of filling the same magnetic material. It was confirmed that the coercive force can be changed.
[0064]
Example 4
The present example relates to the example 3 in which the electrodeposition potential of CoPt was set to a low potential like Co.
In the same manner as in Example 3, after depositing Ti on the Si substrate to a thickness of 10 nm, Cu to a thickness of 20 nm, and Al to a thickness of 200 nm by sputtering, formation of the starting point by FIB and anodization and pore-wide treatment were performed. went.
[0065]
Next, using a reference electrode Ag / AgCl, a large depression was formed by a mixed solution of cobalt (II) sulfate heptahydrate 0.2 mol / L and boric acid 0.3 mol / L at 24 ° C. Co electrodeposition was performed on the nanohole. At this time, the electrodeposition potential is -1.0V.
[0066]
Electrodeposition Co is stopped before Co deposits overflow from the nanohole, and then immersed in 0.01 mol / L KOH aqueous solution at 24 ° C. for 5 minutes to dissolve the bottom alumina of the nanohole formed from a small depression. did.
[0067]
Subsequently, in the same manner as in Example 3, the reference electrode was Ag / AgCl, and an aqueous solution of cobalt (II) sulfate heptahydrate 0.2 mol / L and boric acid 0.3 mol / L and hexachloroplatinic acid hexahydrate CoPt was electrodeposited onto nanoholes formed from small depressions using a mixed solution of 0.1 mol / L mixed at 1: 1 at 24 ° C. In this example, the electrodeposition potential was set to -1.5V.
[0068]
After electrodeposition, the electrodeposits overflowed by surface polishing using a diamond slurry with a particle size of 1/4 μm were removed, annealed in vacuum at 500 ° C. for 10 minutes, and the cross section of the sample was observed with FE-SEM As a result, it was confirmed that all the nanoholes were filled with the electrodeposit.
That is, from this example, it was shown that electrodeposition at a low potential is possible even for nanoholes formed from small depressions by dissolving the bottom alumina.
[0069]
Example 5
The present embodiment relates to recording by a magnetic head in a unit recording area.
Writing was performed on the sample from the surface of the sample produced in Example 3 while applying the pulse magnetic field shown in FIG. 14 using a single pole head. In this embodiment, the unit recording area is a square having a side of about 250 nm, and the unit recording area includes two magnetic cells made of Co and two magnetic cells made of CoPt.
[0070]
After writing, the surface was observed with MFM. As a result, the contrast of the MFM image corresponds to the recording magnetic field by the single magnetic pole head, and four-value recording on the sample by the magnetic head was confirmed. In addition, the magnetic cells that cause magnetization reversal against the recording magnetic field due to the magnetic interaction between adjacent magnetic cells are not confirmed, and the magnetic partition between the magnetic cells is separated by an alumina partition between the magnetic cells. It was confirmed that the bond was broken to some extent.
[0071]
【The invention's effect】
As described above, according to the present invention, a magnetic recording medium that realizes multi-value recording of binary or higher from conventional binary recording is provided, and recording density is improved, that is, high density in the same recording area is achieved. A possible effect is obtained.
[0072]
In addition, the magnetic recording medium capable of multi-value recording according to the present invention is like a continuous medium because each magnetic cell is separated by a non-magnetic material and the magnetic coupling between the magnetic cells is cut off to some extent. It becomes possible to suppress the magnetization reversal caused by the strong interaction between the magnetic domains.
According to the manufacturing method of the present invention, the above-described magnetic recording medium capable of multi-value recording can be easily obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a magnetic recording medium in the present invention.
FIG. 2 is a diagram schematically showing a magnetization curve of a magnetic recording medium in the present invention.
FIG. 3 is a schematic view showing the structure of an alumite film.
FIG. 4 is a process diagram showing the first half of an example of the method for producing a magnetic recording medium of the present invention.
FIG. 5 is a process chart showing the second half of an example of the method for producing a magnetic recording medium of the present invention.
FIG. 6 is a process diagram showing another example of a method for manufacturing a magnetic recording medium according to the present invention.
FIG. 7 is a schematic diagram showing the arrangement of a resist layer on the anodized film.
FIG. 8 is a process diagram showing another example of a method for producing a magnetic recording medium of the present invention.
FIG. 9 is a diagram showing depressions in a square array of patterns produced by FIB.
FIG. 10 is a diagram showing a current profile during anodization.
FIG. 11 is a diagram showing a magnetization curve perpendicular to the substrate.
FIG. 12 is a schematic diagram showing the magnetization state of the magnetic recording medium of the present invention.
FIG. 13 is a process diagram showing another example of a method for manufacturing a magnetic recording medium according to the present invention.
FIG. 14 is a diagram showing a pulse magnetic field from a magnetic head.
[Explanation of symbols]
11 Substrate
12 Non-magnetic material
13 Magnetic cell A
14 Magnetic cell B
15 unit recording area
21 Magnetization curve of magnetic material cell A
22 Magnetization curve of magnetic material cell B
23 Magnetization curve of unit recording area
31 Anodized film
32 Nanohole diameter
33 Nanohole spacing
34 Substrate
35 Alumina
36 Nanohole
41 Substrate
42 Conductive layer
43 Anodized film
44 depression
45 Alumina
46 Nanohole A
47 Nanohole B
48 Magnetic body A
49 Magnetic B
51 Nanohole A
52 Nanohole B
53 Bottom Alumina
54 substrates
55 Conductive layer
61 resist layer
62 substrates
63 Conductive layer
64 Anodized film
71 Si substrate
72 Ti
73 Cu
74 Al
75 depression
76 Nanoholes formed from large depressions
77 Nanoholes formed from small depressions
78 Bottom Alumina
79 Alumina
80 Magnetic material
81 Small depression
82 Large depression
83 Si substrate
84 Ti
85 Cu
86 Al
111 Magnetization in nanoholes
112 Si substrate
113 Ti
114 Cu
121 Nanoholes formed from large depressions
122 Bottom Alumina
123 Nanoholes formed from small depressions
124 Si substrate
125 Ti
126 Cu
127 Magnetic material
128 Magnetic material

Claims (5)

Are separated from each other by non-magnetic material on a substrate, a magnetic cell comprising pores filled with magnetic material disposed, and a region where the coercive force is present different types of magnetic substance cells as a unit recording area, said Binary recording is performed on the same type of magnetic cell in the unit recording area, and multi-level recording of binary or more is performed in the unit recording area by combining a plurality of types of the magnetic cells. A method of manufacturing a magnetic recording medium, comprising: a step of forming an anodized film made of a metal having Al as a main component on a substrate; an anodized film of the anodized film; Forming a plurality of types of pores having different shapes in a magnetic material, and filling the plurality of types of pores having different shapes with different types of magnetic materials by changing an electrodeposition potential. A method for manufacturing a recording medium. 2. The magnetic recording medium according to claim 1 , comprising a step of anodizing a metal containing Al as a main component to form preferentially formed pores and non-preferentially formed pores on the substrate. Manufacturing method. The cross-sectional area of the pores are preferentially formed, a manufacturing method of a magnetic recording medium according to claim 1 or 2 larger than the cross-sectional area of the pores is non-preferentially formed. The step of forming the pores, to claim 1 on a metal film composed mainly of Al formed on a substrate provided with a plurality of types of different sizes recesses by anodizing to form a plurality of types of pores 4. A method for producing a magnetic recording medium according to any one of items 3 to 4. The method of manufacturing a magnetic recording medium according according to any one of claims 1 to 4 pores is anodized alumina nanoholes formed by anodic oxidation of metal mainly composed of Al.

Images