JP4429628B2 - Magnetic recording medium and method for manufacturing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium having a very high recording density in which a magnetic layer is formed on a substrate using magnetic nanoparticles, and a method for producing the same.
[0002]
[Prior art]
In order to improve the recording density of the magnetic recording medium, studies have been made to reduce the particle size of the magnetic particles. In a hard disk medium, the magnetic material used is an alloy such as CoCrPt, but the crystal anisotropy energy (Ku) is 10⁶erg / cm^ThreeTherefore, the practical particle size is considered to be about 10 nm from the viewpoint of thermal fluctuation.
[0003]
In order to further reduce the particle size, it is important to use a magnetic material having a higher Ku. The magnetic material is Co_ThreePt, CoPt, CoPt_Three, Fe_ThreePt, FePt, FePt_Three, FePd, MnBi, MnAl, SmCo_Five, Sm₂Co₁₇And intermetallic compounds and alloys. In recent years, film formation by sputtering using these materials has been actively studied, but since the obtained particle size distribution is wide, the signal-to-noise ratio (S / N ratio) is low at present.
[0004]
On the other hand, a useful method for producing nano-sized magnetic particles (magnetic nanoparticles) having a very narrow particle size distribution is a liquid phase synthesis method. For example, Sun et al. Reported a method for producing FePt monodisperse magnetic particles having a diameter in the range of 3 to 10 nm (see Non-Patent Document 1). Non-Patent Document 1 reports that the standard deviation of the size distribution is 5% or less. The size distribution of particles generated by the method described in Non-Patent Document 1 is extremely narrow compared to the size distribution of particles generated by sputtering.
[0005]
Patent Document 1 discloses a method for uniformly arranging such nano-sized magnetic particles on a substrate. Specifically, the particles obtained by the liquid phase synthesis method are coated with an organic stabilizer, dispersed stably in the liquid, then uniformly spread on the substrate, and the solvent is dried at a low speed. The method described in Patent Document 1 is characterized in that it can form a regular structure in which particles are regularly arranged at a uniform interparticle distance.
[0006]
In general, in a hard disk, diamond-like carbon (DLC) is added by a physical method in order to protect a medium from abrasion due to sliding with a head. Similarly, in the magnetic recording medium using the nanoparticles described in Patent Document 1, a DLC film is provided as a protective film on the magnetic particle layer.
[0007]
In the magnetic recording medium described in Patent Document 1, amorphous carbon, amorphous silicon, silicon oxide, or the like can be used in addition to DLC as a material for the protective film. In either case, the protective film is formed by plasma chemical vapor deposition (plasma CVD), reactive sputtering, or the like.
[0008]
[Patent Document 1]
JP 2000-48340 A
[Patent Document 2]
JP-A-8-124148
[Non-Patent Document 1]
S. Sun, C. B. Murray, D. Weller, L. Folks, A. Moser, Science 2000, 287, p. 1989
[Non-Patent Document 2]
V. L. Colvin, J. Am. Chem. Soc. 1992, 114, p.5221
[0009]
[Problems to be solved by the invention]
The method described in Patent Document 1 has a step of removing the organic stabilizer that covers the magnetic particles before the step of forming the protective film made of DLC or another material. The organic stabilizer is removed by heating under vacuum, ultraviolet light exposure or exposure to hydrogen plasma. Sintering between particles may occur in vacuum heating, and oxidation and damage of magnetic particles may occur in exposure to ultraviolet light and hydrogen plasma.
[0010]
On the other hand, when the organic stabilizer is not removed, the adhesion between the protective film and the magnetic particle layer becomes poor, and the protective effect of the protective film cannot be obtained. Therefore, it is difficult to prevent the magnetic particles from being damaged and ensure the adhesion between the magnetic particle layer and the protective film. In a magnetic recording medium using magnetic nanoparticles, a protective film that resists mechanical shock and stress is important, and establishment of an effective method for forming the protective film is desired. Since magnetic nanoparticles are made of a metal material, the magnetic anisotropy decreases when corroded by oxidation or the like. Therefore, it is important to form a protective film in order to suppress such corrosion.
[0011]
In addition to the method described in Patent Document 1, there is a sol-gel method as a method for forming a protective film on a magnetic recording medium (see Patent Document 2). In the magnetic recording medium described in Patent Document 2, since the magnetic layer is formed by a method such as vapor deposition, the structure of the magnetic recording medium using magnetic nanoparticles is different from that of the magnetic layer. In Patent Document 2, a Co—Ni film formed by, for example, oblique vapor deposition is used as the magnetic layer.
[0012]
Since at least the surface of such a magnetic layer is oxidized, a protective film grows by the sol-gel method. On the other hand, when an attempt is made to form a protective film directly on the magnetic nanoparticle layer according to the method described in Patent Document 2, the protective film does not grow on the surface of the magnetic nanoparticle made of an unoxidized metal material.
[0013]
The present invention has been made in view of the above problems. Therefore, the present invention provides a high recording density magnetic layer made of magnetic nanoparticles and a protective film that imparts corrosion resistance and wear resistance to the magnetic layer. It is an object to provide a magnetic recording medium having the following.
It is another object of the present invention to provide a method for manufacturing a magnetic recording medium that can form a protective film on a magnetic layer made of magnetic nanoparticles without damaging the magnetic nanoparticles.
[0014]
[Means for Solving the Problems]
  In order to achieve the above object, a magnetic recording medium of the present invention includes a substrate, an affinity material layer formed on the substrate, to which magnetic nanoparticles are bound, and a layer formed on the affinity material layer. The magnetic nanoparticles and the magnetic nanoparticles formed on the magnetic nanoparticles, A silane coupling agent, a titanium coupling agent, an aluminum coupling agent, a zirconium coupling agent, or a combination of two or more thereofIt has a coupling agent layer and an inorganic protective film formed on the coupling agent layer by a sol-gel method.
[0015]
Preferably, the inorganic protective film is made of a mixed phase containing a metal oxide, a metal hydroxide, and an organic metal. Particularly preferably, the inorganic protective film is made of a mixed phase containing oxides, hydroxides and organic substances of zirconium, silicon, titanium and aluminum, or a combination thereof.
[0016]
  Thereby, the adhesiveness of the protective film (inorganic protective film) formed on the magnetic nanoparticle layer can be increased, and the magnetic nanoparticles are protected from abrasion and corrosion. Magnetic nanoparticlesOrganic stabilizers for coatingSince it is removed in the process of forming the coupling agent layer, there is no heating or plasma treatment, and damage to the magnetic nanoparticles is prevented.
[0017]
In order to achieve the above object, the method for producing a magnetic recording medium of the present invention includes a step of forming an affinity material layer to which magnetic nanoparticles are bonded on a substrate, and the magnetic material coated with an organic stabilizer. A step of arranging nanoparticles in a layer form on the affinity material layer, and replacing the organic stabilizer covering the magnetic nanoparticles with a coupling agent, and providing a coupling agent layer on the magnetic nanoparticles And a step of forming an inorganic protective film on the coupling agent layer by a sol-gel method.
[0018]
Preferably, the step of forming the inorganic protective film starts with hydrolysis and dehydration condensation of the starting material in a solution containing the starting material, starting from an alkoxide of any metal of zirconium, silicon, titanium, and aluminum. The step of depositing a mixed phase containing the oxide, hydroxide and organic substance of the metal is included.
[0019]
Alternatively, preferably, the step of forming the inorganic protective film includes a step of depositing silicon oxide by dehydration condensation of the starting material in the aqueous silicate solution using the silicate as a starting material.
[0020]
This makes it possible to form an inorganic protective film that protects the magnetic nanoparticle layer from abrasion and corrosion. According to the method for producing a magnetic recording medium of the present invention, an inorganic protective film is formed on a magnetic nanoparticle by a sol-gel method through a coupling agent layer. By providing the coupling agent layer, the magnetic nanoparticle layer and the inorganic protective film are more closely adhered to each other, and peeling between the layers is prevented. In addition, according to the present invention, since the inorganic protective film can be formed under relatively mild conditions, damage to the magnetic nanoparticles is prevented.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the magnetic recording medium of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a cross-sectional view of a magnetic recording medium according to the present invention. As shown in FIG. 1, a layer made of an affinity material (affinity material layer 2) is formed on a substrate 1, and magnetic nanoparticles 3 are arranged as a single layer on the substrate 1 at a constant interval. A silane coupling agent layer 4 is present on the magnetic nanoparticles, and an inorganic protective film 5 is further present thereon. The silane coupling agent layer 4 may be formed not only on the magnetic nanoparticles 3 but also between the particles.
[0022]
Next, each layer of the magnetic recording medium will be described in detail. As the substrate 1, any substrate made of a conventionally known material can be used. The form of the substrate 1 is not limited to a disk shape or a card shape. Examples of the substrate 1 include silicon and silicon oxide (SiO₂), A hard substrate such as magnesium oxide (MgO), and a soft substrate such as polyimide.
[0023]
The affinity material layer 2 includes an affinity material that attracts and holds the magnetic nanoparticles 3. The affinity material layer 2 has a functional group that binds or adsorbs to magnetic nanoparticles on the surface. The affinity material layer 2 attracts and holds the magnetic nanoparticles 3 so that the magnetic nanoparticles 3 can be arranged in a single layer. In addition, since the affinity material layer 2 holds the magnetic nanoparticles 3, dropping of the magnetic nanoparticles 3 when the silane coupling agent layer 4 is formed is suppressed.
[0024]
The affinity material layer 2 is formed by immersing the substrate 1 in a solution (affinity material solution) in which the affinity material is dissolved, or by applying the affinity material solution to the substrate 1 by a method such as spin coating. The Alternatively, the affinity material layer 2 can be formed by the Langmuir-Blodgett method. The affinity material is represented by the following formula (2).
[0025]
[Chemical 2]
X²-R²-Y²  ... (2)
[0026]
Where R²Represents hydrocarbon and fluorocarbon chains containing 3 to 18 carbon atoms, X²And Y²Is -SO₂OH, -SOOH, -POOH, -OPO (OH)₂, -COOH, -NH₂Selected from. The affinity material may be selected from silane coupling agents used for the silane coupling agent layer 4.
[0027]
In addition, when the affinity material which comprises the affinity material layer 2 contains a thiol group, the magnetism of the magnetic nanoparticle 3 may change, and the recording characteristics of a magnetic recording medium may be impaired. Non-Patent Document 2 reports that a self-assembled monolayer of hexanedithiol was formed on a gold substrate, and CdS nanoparticles were immobilized on thiol groups present on the film surface.
[0028]
However, when the magnetic nanoparticles are similarly adsorbed to the thiol group, the transition metal contained in the magnetic nanoparticles is ionized, and the thiol group and the transition metal ion form a complex. When the transition metal dissolves into the solution from the magnetic nanoparticles and the alloy composition of the magnetic nanoparticles changes, the magnetism of the magnetic nanoparticles 3 may deteriorate. Therefore, it is preferable that the affinity material does not alter the magnetic nanoparticles 3 (see Japanese Patent Application No. 2002-249854).
[0029]
The magnetic nanoparticles 3 are arranged on the affinity material layer 2 in the form of a single layer or multiple layers. Magnetic nanoparticles 3 are made of magnetic materials such as elements Co, Fe, Ni, Mn, Sm, Al, Pd, Pt, intermetallic compounds of these elements, or multi-element alloys such as binary alloys and ternary alloys of these elements. including.
[0030]
The magnetic nanoparticles 3 used in the magnetic recording medium of this embodiment are preferably those synthesized in a liquid phase. The liquid phase synthesis method is a method in which a metal salt, an organic metal, or the like is dissolved in a liquid and particles are precipitated by reduction or decomposition (see Non-Patent Document 1). Known liquid phase synthesis methods for synthesizing fine particles include a coprecipitation method, a hot soap method, and a reverse micelle method. The particle diameter is preferably 10 nm or less. The standard deviation of the particle diameter is 20% or less, preferably 10% or less, more preferably 5% or less. The narrower the standard deviation of the particle diameter, the lower the medium noise during reproduction, and a higher S / N ratio can be obtained.
[0031]
FIG. 2A is a cross-sectional view showing the manufacturing process of the magnetic recording medium of the present embodiment, and shows a state in which the magnetic nanoparticles 3 are arranged in layers on the affinity material layer 2. As shown in FIG. 2 (a), the magnetic nanoparticles 3 are coated with an organic stabilizer 6, and the magnetic nanoparticles are regularly arranged with a certain distance therebetween. Since the functional group present on the surface of the affinity material layer 2 preferentially binds and adsorbs to the magnetic nanoparticles 3, the organic stabilizer 6 is formed at the interface between the magnetic nanoparticles 3 and the affinity material layer 2. Drop off from 3.
[0032]
The layer of the magnetic nanoparticles 3 shown in FIG. 2A can be formed in the same manner as the method described in Patent Document 1, for example. That is, it is formed by coating the magnetic nanoparticles 3 with the organic stabilizer 6, stably dispersing in the liquid, spreading on the substrate, and drying the solvent at a low speed.
[0033]
Preferably, the organic stabilizer 6 is represented by the following formula (3).
[Chemical Formula 3]
R^Three-X^Three  ... (3)
[0034]
Where R^ThreeRepresents a long or branched hydrocarbon chain containing 6 to 22 carbon atoms, or a long or branched fluorocarbon chain containing 6 to 22 carbon atoms. X^ThreeIs a group adsorbed on the surface of the magnetic nanoparticle and represents carboxylic acid, phosphonic acid, phosphinic acid, sulfonic acid, sulfinic acid, amine, or diamine.
[0035]
FIG.2 (b) is the schematic diagram which expanded the organic stabilizer 6 of Fig.2 (a). As shown in FIGS. 2 (a) and (b), the organic stabilizer 6 is an X of the formula (3).^ThreeThe terminal functional group represented by is bonded to or adsorbed to the magnetic nanoparticles 3. Further, R in the formula (3)^ThreeIs located on the solution side and suppresses aggregation of the magnetic nanoparticles.
[0036]
The silane coupling agent layer 4 is obtained by immersing the substrate in a solution (silane coupling agent solution) in which the silane coupling agent is dissolved at a predetermined concentration, or the silane coupling agent solution is placed on the magnetic nanoparticle 3 layer. It is formed by applying to. The silane coupling agent which comprises the silane coupling agent layer 4 is shown by Formula (1).
[0037]
[Formula 4]
(R¹O)_aY¹ _3-aSi- (CH₂)_l-(C₆H_Four)_m-(CH₂)_n-X¹  ... (1)
[0038]
Where R¹Represents a lower alkyl group having 1 to 3 carbon atoms or hydrogen, Y¹Represents a lower alkyl group, a phenyl group or chlorine, and X¹Is -NH₂, -NH- (CH₂)_x-NH₂(X = 2-6), -NH- (CH₂)₂-NH- (CH₂)₂-NH₂, -NH-CO-NH₂, -NH- (CH₂)_x-CH_Three(X = 0-3), -NH-CH- (CH_Three)₂, -NH-C₆H_Five, -NH- (C₂H_FourOH), -NH-CH₂-CH = CH₂, -N- (CH_Three)₂, -N- (C₂H_Five)₂, -N- (C₂H_FourOH)₂, -COOH, -OPO (OH)₂, -POOH, -SO₂OH or -SOOH is represented, a represents an integer of 1 to 3, and l, m, and n represent an integer of 0 to 17. C₆H_FourRepresents a phenyl group.
[0039]
The above silane coupling agent has a terminal functional group X¹Is bonded to the magnetic nanoparticle 3 and exists in a form in which the alkoxide at the other end or a silanol group generated by hydrolysis of the alkoxide is directed to the opposite side to the magnetic nanoparticle 3. The alkoxide and silanol group of the silane coupling agent layer 4 serve as a starting point for the growth of the inorganic protective film 5 in the film formation by the sol-gel method.
[0040]
As long as the magnetic nanoparticles 3 are adsorbed to the magnetic nanoparticles 3 without alteration and the inorganic protective film 5 is grown by the sol-gel method, a layer made of another coupling agent is used instead of the silane coupling agent layer 4. May be formed. Examples of the coupling agent other than the silane coupling agent include a titanium coupling agent, an aluminum coupling agent, and a zirconium coupling agent.
[0041]
FIG. 2C is a cross-sectional view showing the manufacturing process of the magnetic recording medium of this embodiment, and shows a state in which the silane coupling agent layer 4 is formed on the magnetic nanoparticle 3 layer. As shown in FIG. 2C, the organic stabilizer 6 in FIG. 2A is substituted by the functional group of the silane coupling agent constituting the silane coupling agent layer 4 and desorbed. The silane coupling agent layer 4 is bonded to the magnetic nanoparticles 3 through the functional group of the silane coupling agent.
[0042]
The inorganic protective film 5 is formed using a sol-gel method. When the inorganic protective film 5 is formed, the surface of the silane coupling agent layer 4 is exposed to alkoxy groups, silanol groups generated by hydrolysis of alkoxy groups, condensates thereof, or the like. An alkoxide or silanol group present on the surface of the silane coupling agent layer 4 is the starting point, and hydrolysis or condensation polymerization of the alkoxide occurs on the surface of the silane coupling agent layer 4. Thereby, the inorganic protective film 5 is formed as shown in FIG.
[0043]
The inorganic protective film 5 is made of a mixed phase containing a metal oxide, a metal hydroxide and an organic metal. The inorganic protective film 5 improves the wear resistance and corrosion resistance of the layer made of the magnetic nanoparticles 3. The inorganic protective film 5 is preferably a thin film made of any one of a mixed phase material containing zirconium, silicon, titanium, aluminum oxide, hydroxide and organic metal, or a combination thereof.
[0044]
In the formation of the inorganic protective film 5 using the sol-gel method, a metal alkoxide is used as a starting material, and the metal oxide is formed on the silane coupling agent layer 4 using hydrolysis and dehydration condensation in a solution. A mixed phase comprising a hydroxide and an organometallic is deposited. As the metal alkoxide, tetramethoxyzirconium, tetraethoxysilane, triisopropoxyaluminum, tetraisopropoxytitanium, or the like is used.
[0045]
The metal alkoxide solvent is a mixed solvent of an organic solvent and water, and the pH is preferably adjusted to 9-12. The type of organic solvent is not particularly limited as long as it dissolves metal alkoxide and is arbitrarily mixed with water, but ethanol, methanol, isopropanol, n-propanol, 2-methoxyethanol, 2-ethoxyethanol and the like are preferable. The inorganic protective film 5 is formed on the surface by immersing the substrate in a metal alkoxide solution for a predetermined time.
[0046]
It is also possible to deposit silicon oxide (silica) as an inorganic protective film 5 on the silane coupling agent layer 4 using an aqueous silicate solution as a starting material. In this case, the pH of the solution is set to 8-11. As the silicate aqueous solution, a sodium silicate solution is preferable. As in the case of using a metal alkoxide solution, the silica film is formed on the surface by immersing the substrate in an aqueous silicate solution for a certain time.
[0047]
The thickness of the inorganic protective film 5 is preferably 20 nm or less. When the film thickness is 20 nm or more, the signal intensity from the magnetic nanoparticle 3 is remarkably lowered, which seriously hinders the S / N ratio. When the metal alkoxide is used as a starting material, the thickness of the inorganic protective film 5 is controlled by the alkoxide concentration, water content, pH, and immersion time. On the other hand, when an aqueous silicate solution is used as a starting material, the concentration is controlled by the solution concentration, pH, and immersion time.
[0048]
In the magnetic recording medium of the present embodiment, it is preferable to provide a lubricant layer on the inorganic protective film 5 because the wear resistance of the magnetic recording medium can be further improved. As the lubricant, conventionally known ones can be used, and examples thereof include silicone oils such as higher fatty acid esters, higher fatty acids, fluorocarbons, dialkylpolysiloxanes, fluoroalkylpolysiloxanes, and oligomers thereof, or combinations thereof. It is done. The lubricant layer can be formed by applying a solution obtained by dissolving the above-described lubricant in an organic solvent onto the inorganic protective film 5 by, for example, spin coating.
[0049]
FIG. 3 is a flowchart showing a method of manufacturing a magnetic recording medium according to the present invention. As shown in FIG. 3, first, an affinity material layer is formed on a substrate (step (ST) 1). Disperse the magnetic nanoparticles in the solution with an organic stabilizer (step 2) and immerse the substrate in the solution, or apply the solution on the affinity material layer and layer the magnetic nanoparticles on the affinity material layer. (Step 3). At this time, the magnetic nanoparticles are coated with an organic stabilizer except for the interface with the affinity material layer. Next, the organic stabilizer is replaced with a silane coupling agent to form a silane coupling agent layer on the magnetic nanoparticle layer (step 4). Thereafter, an inorganic protective film is formed on the silane coupling agent layer by a wet process (sol-gel method) (step 5).
[0050]
As a comparative example of the flowchart of FIG. 3, a method of manufacturing a magnetic storage medium described in Patent Document 1 is shown in FIGS. FIG. 4 is a flowchart when an affinity material layer is not formed between the substrate and the magnetic nanoparticle layer, and FIG. 5 is a flowchart when this affinity material layer is formed. In the method described in Patent Document 1, the formation of the affinity material layer is not essential.
[0051]
In the case of the manufacturing method shown in FIG. 4, first, magnetic nanoparticles are dispersed in a solution with an organic stabilizer (step (ST) 1), and the magnetic nanoparticles coated with the organic stabilizer are arranged in layers on the substrate. (Step 2). Next, the organic stabilizer is removed by heating under vacuum, ultraviolet light exposure or exposure to hydrogen plasma (step 3). Thereafter, a protective film is formed on the magnetic nanoparticle layer by a dry process, specifically, a vacuum thin film forming technique such as CVD or reactive sputtering (step 4).
[0052]
On the other hand, in the case of the manufacturing method shown in FIG. 5, first, an affinity material layer is formed on a substrate (step (ST) 1). Next, the magnetic nanoparticles are dispersed in the solution with an organic stabilizer (step 2), and the magnetic nanoparticles coated with the organic stabilizer are arranged in layers on the affinity material layer (step 3). Next, the organic stabilizer is removed by heating under vacuum, ultraviolet light exposure or exposure to hydrogen plasma (step 4). Thereafter, a protective film is formed on the magnetic nanoparticle layer by a dry process, specifically, a vacuum thin film forming technique such as CVD or reactive sputtering (step 5).
[0053]
As is clear when comparing FIG. 3 with FIG. 4 or FIG. 5, according to the flow of the present invention shown in FIG. 3, the physical organic stabilizer is not removed before the formation of the inorganic protective film. Damage to the magnetic nanoparticles is prevented. Further, by forming a silane coupling agent layer (step 4 in FIG. 3), it is possible to form an inorganic protective film by the sol-gel method (step 5).
[0054]
【Example】
The present invention will be described below based on examples, but the present invention is not limited to these examples.
Example 1
3- (2-aminoethyl) aminopropyltrimethoxysilane (APTS, (CH) as an affinity material layer on a silicon wafer with a thermal oxide film (surface roughness Ra = 0.2 nm)_ThreeO)_ThreeSi (CH₂)_ThreeNHCH₂CH₂NH₂) Layer was formed. This is the first APTS layer.
[0055]
Subsequently, magnetic nanoparticles (FePt particles) having a particle diameter of 3 nm synthesized in the liquid phase were arranged in a single layer on the first APTS layer. FIG. 6 shows a scanning electron microscope (SEM) photograph of a medium in which FePt particles are arranged on the first APTS layer. Compared to APTS, which is an organic compound, FePt particles made of metal have higher reflectance, so in the SEM image, the APTS part becomes dark and the FePt particle part becomes white.
[0056]
As shown in FIG. 6, the FePt particles are not aggregated but are dispersed on the first APTS layer. The thickness of the layer of FePt particles was obtained from the SEM photograph of FIG. 6 and the X-ray reflectivity, and it was confirmed that the FePt particles were arranged in a single layer. As the organic stabilizer for dispersing the FePt particles, oleic acid was used.
[0057]
The substrate on which the single layer of FePt particles was formed was immersed in an APTS ethanol solution and taken out after 30 minutes. Thereby, the 2nd APTS layer was formed as a silane coupling agent layer. The substrate on which the silane coupling agent layer was formed was immersed in a 0.1 vol% ethanol / water mixed solution of tetraethoxysilane (TES) for 20 hours, and an inorganic protective film was grown by a sol-gel method.
[0058]
Where ethanol / water ratio is 4, NH_ThreeThe pH was adjusted to 10. After immersing the substrate in the TES solution, the substrate was washed with a solvent and dried, and further heat-treated at 120 ° C. in the atmosphere. Thus, a silicon compound film containing silicon oxide and hydroxide was formed as the inorganic protective film. A part of the alkoxy group (ethoxy group) of TES also remains in this silicon compound film.
[0059]
If the ethoxy group of TES is completely hydrolyzed and the silanol group generated by hydrolysis of the ethoxy group is completely dehydrated and condensed, the composition of the silicon compound film is silicon oxide (SiO 2₂However, under the actual reaction conditions, these reactions do not proceed completely. Therefore, a mixed phase silicon compound film is obtained.
[0060]
FIG. 7A shows an atomic force microscope (AFM) image of a medium in which a silane coupling agent layer is formed on FePt particles and an inorganic protective film is further formed thereon. FIG. 7B shows an AFM image of a medium in which the silane coupling agent layer is formed on the FePt particles and the inorganic protective film is not formed. FIG. 7C shows an AFM image of a medium in which only FePt particles are arranged and a silane coupling agent layer and an inorganic protective film are not formed on the FePt particles.
[0061]
The medium in which the silane coupling agent layer in FIG. 7B is formed is almost equivalent to the AFM image of the medium having only FePt particles in FIG. In contrast, in the medium on which the inorganic protective film in FIG. 7A was formed, particulate precipitates were observed on the surface. In FIG. 7A, white dotted portions correspond to particulate precipitates.
[0062]
FIG. 8 shows a cross-sectional transmission electron microscope (cross-section TEM) image of the magnetic recording medium of Example 1. From FIG. 8, it can be seen that a laminated film of a silane coupling agent layer (second APTS layer) 4 and an inorganic protective film (silicon compound film) 5 is formed on the FePt particles 3 with a total thickness of about 15 nm. I can confirm.
[0063]
Since the APTS layer and the silicon compound film are close in density and have no difference in contrast, these layers cannot be separated and identified by a cross-sectional TEM image. Further, it can be confirmed from FIG. 8 that an affinity material layer (first APTS layer) is interposed between the FePt particles 3 and the substrate (silicon wafer with thermal oxide film) 1.
[0064]
(Example 2)
A first APTS layer was formed as an affinity material layer on a silicon wafer with a thermal oxide film (surface roughness Ra = 0.2 nm). Subsequently, FePt particles with a particle diameter of 3 nm synthesized in the liquid phase were arranged in a single layer on the first APTS layer. The substrate on which the single layer of FePt particles was formed was immersed in an APTS ethanol solution and taken out after 30 minutes. Thereby, the 2nd APTS layer was formed as a silane coupling agent layer. The above steps were performed in the same manner as in Example 1.
[0065]
The substrate on which the silane coupling agent layer was formed was immersed in a 1 wt% aqueous solution of sodium silicate for 4 hours, and an inorganic protective film was grown by a sol-gel method. Here, the pH of the solution was adjusted to 10 with an anion exchange resin. The aqueous solution of sodium silicate is silicon oxide (SiO₂In order to prevent the precipitation of), the pH is adjusted to alkaline of 12-14. When the pH is high, film formation by the sol-gel method is difficult to proceed, and the pH of the solution is adjusted as necessary. The means for adjusting the pH is not limited to the anion exchange resin, and for example, the pH may be adjusted by adding an acid.
[0066]
After immersing the substrate in a sodium silicate solution, the substrate was washed with a solvent and dried, and further heat-treated at 120 ° C. in the air. Thus, a silicon compound film containing silicon oxide and hydroxide was formed as the inorganic protective film. Also in this case, as in Example 1, it is difficult to completely control the composition of the silicon compound, and a mixed phase amorphous film is obtained as the silicon compound film. Also for the magnetic recording medium of Example 2 produced as described above, it was confirmed by cross-sectional TEM observation that a silane coupling agent layer and an inorganic protective film were formed on the FePt particles with a total thickness of 15 nm.
[0067]
(Example 3)
A first APTS layer was formed as an affinity material layer on a silicon wafer with a thermal oxide film (surface roughness Ra = 0.2 nm). Subsequently, FePt particles with a particle diameter of 3 nm synthesized in the liquid phase were arranged in a single layer on the first APTS layer. The substrate on which the single layer of FePt particles was formed was immersed in an APTS ethanol solution and taken out after 30 minutes. Thereby, the 2nd APTS layer was formed as a silane coupling agent layer. The above steps were performed in the same manner as in Example 1.
[0068]
The substrate on which the silane coupling agent layer was formed was immersed in a 0.1 vol% isopropanol / water solution of tetraisopropoxyaluminum heated to 60 ° C. for 2 hours, and an inorganic protective film was grown by a sol-gel method. Where the isopropanol / water ratio is 100, NH_ThreeThe pH was adjusted to 10.
[0069]
After the substrate was immersed in a solution of tetraisopropoxyaluminum, the substrate was washed with a solvent and dried, and further heat-treated at 120 ° C. in the atmosphere. As a result, an aluminum compound film containing aluminum oxide and hydroxide was formed as the inorganic protective film.
[0070]
Also in this case, as in Example 1, it is difficult to completely control the composition of the aluminum compound, and a mixed-phase amorphous film can be obtained as the aluminum compound film. Also for the magnetic recording medium of Example 3 produced as described above, it was confirmed by cross-sectional TEM observation that a silane coupling agent layer and an inorganic protective film were formed on the FePt particles with a total thickness of 10 nm.
[0071]
According to the magnetic recording medium of the above-described embodiment of the present invention, the magnetic nanoparticle layer is covered with the inorganic protective film, and wear of the magnetic nanoparticle layer and corrosion of the magnetic nanoparticle are prevented. Therefore, deterioration of the magnetic characteristics of the magnetic recording medium is prevented.
In addition, according to the method for manufacturing a magnetic recording medium of the above-described embodiment of the present invention, an inorganic protective film can be formed on the surface of the magnetic recording medium on the order of nanometers by utilizing a sol-gel reaction in a liquid phase. A magnetic recording medium having excellent wear and corrosion resistance can be produced.
[0072]
Embodiments of the magnetic recording medium of the present invention are not limited to the above description. For example, the thickness of the silane coupling agent layer and the inorganic protective film formed on the magnetic nanoparticles can be appropriately changed in consideration of wear resistance or corrosion resistance. Moreover, the film-forming conditions of an inorganic protective film can be suitably changed according to the material used. In addition, various modifications can be made without departing from the scope of the present invention.
[0073]
【The invention's effect】
According to the magnetic recording medium of the present invention, the high recording density magnetic layer made of magnetic nanoparticles is protected from abrasion and corrosion by the inorganic protective film.
According to the method for producing a magnetic recording medium of the present invention, an inorganic protective film can be formed on a layer of magnetic nanoparticles without damaging the magnetic nanoparticles.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a magnetic recording medium of the present invention.
2 (a) and 2 (c) are cross-sectional views showing the production steps of the method for producing a magnetic recording medium of the present invention, and FIG. 2 (b) shows the organic stabilizer of FIG. 2 (a). FIG.
FIG. 3 is a flowchart showing a method for manufacturing a magnetic recording medium of the present invention.
FIG. 4 is a flowchart showing a comparative example of a method for manufacturing a magnetic recording medium according to the present invention.
FIG. 5 is a flowchart showing a comparative example of a method for manufacturing a magnetic recording medium according to the present invention.
6 shows an SEM photograph of a magnetic recording medium according to Example 1 of the present invention in which magnetic nanoparticles (FePt particles) are arranged on an affinity material layer (first APTS layer). FIG.
7A to 7C show AFM images of the magnetic recording medium according to Example 1 of the present invention. FIG.
FIG. 8 shows a cross-sectional TEM image of the magnetic recording medium according to Example 1 of the invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Affinity material layer, 3 ... Magnetic nanoparticle, 4 ... Silane coupling agent, 5 ... Inorganic protective film, 6 ... Organic stabilizer.

Claims (20)

A substrate,
An affinity material layer formed on the substrate to which magnetic nanoparticles are bound;
The magnetic nanoparticles arranged in layers on the affinity material layer;
A coupling agent layer formed on the magnetic nanoparticles and selected from a silane coupling agent, a titanium coupling agent, an aluminum coupling agent, a zirconium coupling agent, or a combination of two or more thereof ;
A magnetic recording medium comprising an inorganic protective film formed by a sol-gel method on the coupling agent layer. The magnetic recording medium according to claim 1, wherein the inorganic protective film is made of a mixed phase containing a metal oxide, a metal hydroxide, and an organic metal. The magnetic recording according to claim 2, wherein the inorganic protective film is made of zirconium (Zr), silicon (Si), titanium (Ti), aluminum (Al) oxide, a mixed phase containing a hydroxide and an organic substance, or a combination thereof. Medium. The magnetic recording medium according to claim 1, wherein the inorganic protective film has a thickness of 20 nm or less. The magnetic recording medium according to claim 1, wherein the magnetic nanoparticles are arranged in a single layer on the affinity material layer. The magnetic recording medium according to claim 1, wherein the magnetic nanoparticles are arranged in multiple layers on the affinity material layer. The magnetic recording medium according to claim 1, wherein the coupling agent layer is also formed between the magnetic nanoparticles. The magnetic nanoparticles include elemental cobalt (Co), iron (Fe), nickel (Ni), manganese (Mn), samarium (Sm), aluminum, palladium (Pd), platinum (Pt), an intermetallic compound of the element, The magnetic recording medium according to claim 1, comprising a magnetic material selected from the group consisting of multi-element alloys of binary elements or more of the elements. The magnetic recording medium according to claim 1, wherein the magnetic nanoparticles have a diameter of 10 nm or less. The magnetic recording medium according to claim 1, wherein the coupling agent layer includes a silane coupling agent. The silane coupling agent is represented by the following formula (1).

(In the formula, R ¹ represents a lower alkyl group having 1 to 3 carbon atoms or hydrogen, Y ¹ represents a lower alkyl group, a phenyl group or chlorine, and X ¹ represents —NH ₂ , —NH— (CH _{2 ) x -NH 2 (x = 2~6} ), - NH- (CH 2) 2 -NH- (CH 2) 2 -NH 2, -NH-CO-NH 2, -NH- (CH 2) x - _{CH 3 (x = 0~3),} - NH-CH- (CH 3) 2, -NH-C 6 H 5, -NH- (C 2 H 4 OH), - NH-CH 2 -CH = CH 2 _{, -N- (CH 3) 2,} -N- (C 2 H 5) 2, -N- (C 2 H 4 OH) 2, -COOH, -OPO (OH) 2, -POOH, -SO 2 OH or an -SOOH, a is _.C 6 _{H 4} 1 to 3 of an integer, l, m, n is an integer of 0 to 17 represents a phenyl group )
The magnetic recording medium according to claim 10. The magnetic recording medium according to claim 1, further comprising a lubricant layer containing a lubricant on the inorganic protective film. The magnetic recording medium according to claim 12, wherein the lubricant layer contains one or more silicon oils or oligomers selected from the group consisting of higher fatty acid esters, higher fatty acids, fluorocarbons, dialkylpolysiloxanes, and fluoroalkylpolysiloxanes. Forming on the substrate an affinity material layer to which the magnetic nanoparticles bind;
Arranging the magnetic nanoparticles coated with an organic stabilizer in layers on the affinity material layer;
Replacing the organic stabilizer that coats the magnetic nanoparticles with a coupling agent to form a coupling agent layer on the magnetic nanoparticles;
And a step of forming an inorganic protective film on the coupling agent layer by a sol-gel method. The step of forming the inorganic protective film includes starting with an alkoxide of a metal of zirconium, silicon, titanium, or aluminum as a starting material, and performing hydrolysis and dehydration condensation of the starting material in a solution containing the starting material. The method for producing a magnetic recording medium according to claim 14, further comprising the step of depositing a mixed phase containing the oxide, hydroxide and organic substance. The method for producing a magnetic recording medium according to claim 15, wherein the solvent of the solution containing the starting material is a mixed solvent containing alcohol and water, and the pH of the solution is 9 to 12. The process of forming the said inorganic protective film includes the process of depositing a silicon oxide by dehydration condensation of the said starting material in the said silicate aqueous solution using the silicate as a starting material. Method. The method of manufacturing a magnetic recording medium according to claim 17, wherein the pH of the aqueous solution is 8 to 11. The magnetic recording medium according to claim 14, wherein the step of arranging the magnetic nanoparticles in the form of a layer on the affinity material layer includes a step of immersing the substrate in a solution containing the magnetic nanoparticles and the organic stabilizer. Manufacturing method. 15. The step of arranging the magnetic nanoparticles in a layer form on the affinity material layer includes a step of applying a solution containing the magnetic nanoparticles and the organic stabilizer on the affinity material layer. Manufacturing method of magnetic recording medium.

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