JP2777656B2 - Magnetic recording media - Google Patents

Description

The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium suitable for perpendicular magnetic recording and magneto-optical recording.

[Problems to be solved by conventional technology and invention]

Recently, attempts have been made to form a spinel-type ferrite film by a sputtering method and apply the film to a perpendicular magnetic recording medium or a magneto-optical recording medium. Since this spinel-type ferrite has a cubic crystal structure and has no uniaxial anisotropy, it is not possible to produce a perpendicular magnetization film utilizing crystal magnetic anisotropy. There have been some reports that a perpendicular magnetization film has been made of Co spinel ferrite or iron oxide (for example, IEEE Transactions on Magnetics, MAG-
12, No. 6, p. 773-775 (November 1976) and MAG-20, No. 5,
P.1007-1012 (September 1984), 9th Annual Meeting of the Japan Society of Applied Magnetics, 29pB-7, p312 and 29pB-10, p315 (1985)
November), JP-A-59-45644, JP-A-60-124901, JP-A-60-150248, etc.), all of which are considered to utilize magnetic anisotropy caused by strain. . Specifically, a spinel-type ferrite film having a large coefficient of thermal expansion is formed at a high temperature (500 ° C. or more) on a glass substrate having a small coefficient of thermal expansion (quartz glass, Vycor, etc.) A tensile stress is generated in the ferrite film, and perpendicular magnetic anisotropy is generated.

However, in this case, the substrate material is limited to a material having a smaller coefficient of thermal expansion to some extent than the ferrite film. The film must be made at high temperature. The adhesive strength between the glass substrate and the ferrite film is not very strong, and the strain is removed with the passage of time, and the perpendicular magnetic anisotropy decreases.

On the other hand, a ferrite film was produced epitaxially on a single crystal substrate,
Although a method of creating anisotropy due to strain has been proposed, in this case, although the above problems are eliminated, a single crystal substrate is generally expensive and easily broken, and a large-sized substrate is obtained. Is difficult, so it is difficult to put it to practical use.

The present invention has been made in order to solve such problems of the prior art, and can use general glass, metal, plastic, and the like as a substrate, can form a magnetic recording layer at a low temperature, and can perform a long-term operation. It is an object of the present invention to provide a magnetic recording medium that uses a spinel-type ferrite perpendicular magnetization film as a magnetic recording layer, which is stable and inexpensive.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, an underlayer made of a crystalline film having a spinel type crystal structure and a magnetic recording layer made of a spinel type ferrite crystalline film are sequentially laminated on a substrate. A magnetic recording medium, wherein the lattice constant of the underlayer is larger than the lattice constant of the magnetic recording layer.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing the most basic layer configuration of a magnetic recording medium according to the present invention. As shown in the figure, the magnetic recording medium of the present invention is basically constituted by sequentially laminating a base layer 2 having a spinel-type crystal structure on a substrate 1 and a magnetic recording layer 3 made of spill-type ferrite. In addition, the lattice constant of the underlayer 2 is larger than the lattice constant of the magnetic recording layer 3.

Examples of the substrate 1 include metals such as Al, Al alloys, stainless steels, resins such as polymethyl methacrylate (PMMA), polycarbonate (PC), epoxy, soda glass, borosilicate glass, barium borosilicate glass, and aluminosilicate. Glass such as glass can be used, and the thickness is suitably about 0.1 to 2 mm.

The underlayer 2 is formed using a material represented by the following formula (I).

AB ₂ O ₄ (where A is a metal element which becomes a divalent ion, B is a metal element which becomes a trivalent ion) (I) Mg, Mn, Co, Ni, Cu, Zn, Fe, etc. And B is one or more selected from Cr, In, Rh, Sc, Tl, Fe and the like. However, as a special case, A contains monovalent ions and trivalent ions instead of divalent ions, and B simultaneously contains divalent ions and tetravalent ions instead of trivalent ions. There are things. As a film forming method, a vapor deposition method, a sputtering method, or a CVD method is used, and its film thickness is suitably about 0.05 to 5 μm.

The magnetic recording layer 3 is formed using a material represented by the following formula (II).

AB _x Fe _2-x O ₄ (The conditions of A and B are the same as in the formula (I).
And 0 ≦ x <2. ) (II) As in the case of the underlayer 2, a vapor deposition method, a sputtering method, a CVD method, or the like is used for forming the magnetic recording layer 3, and the film thickness is 0.05 to
About 5 μm is appropriate.

When the lattice constant of the underlayer 2 is larger than the lattice constant of the magnetic recording layer 3, the spinel ferrite crystal formed thereon has
Since there is a tendency to be aligned with the atomic arrangement of the underlayer, the shape is elongated in the in-plane direction by the difference of the lattice constant. At the same time, it shrinks in the direction perpendicular to the film surface, and as a result, lattice distortion occurs. In other words, the lattice spacing of the magnetic recording layer 3 hardly differs from that of the underlayer 2 in the in-plane direction of the film, and becomes smaller than the original value of the magnetic recording material in the direction perpendicular to the film. For the above reasons, spinel ferrite, which is originally a cubic crystal structure having no uniaxial anisotropy, changes to a tetragonal crystal structure having uniaxial anisotropy, and a large perpendicular magnetic anisotropy occurs in the magnetic recording layer 3. Anisotropy is induced. In this case, since the occurrence of perpendicular magnetic anisotropy is caused by the difference between the two lattice constants, there is no longer the restriction on the coefficient of thermal expansion with respect to the substrate as in the prior art. Resin can be used, and cost can be reduced. The underlayer 2 and the magnetic recording layer 3
, The perpendicular magnetic anisotropy does not decrease over time, and the characteristics are stable for a long time.

Since the lattice constant of the spinel ferrite constituting the magnetic recording layer 3 is usually 8.3 to 8.5 °, the lattice constant of the underlayer 2 is
It is preferably about 8.4 to 8.7 ° and satisfies the above conditions. The magnitude of the lattice constant between the underlayer 2 and the magnetic recording layer 3 can be controlled by a combination of A and B in the above formulas (I) and (II).

In the present invention, it is preferable that the underlayer 2 and the magnetic recording layer 3 are made of a polycrystalline film and their crystal orientations are oriented. That is, the crystal orientation of the underlayer 2 is set to (10
The (0), (110), and (111) planes are oriented so as to be parallel to the film surface, and the magnetic recording layer 3 is also oriented in the same direction as the underlayer. By doing so, the perpendicular magnetic anisotropy can be further increased, and the stability and readout characteristics in perpendicular magnetic recording and magneto-optical recording can be improved. The orientation and degree of orientation of the underlayer 2 can be controlled by the substrate temperature, oxygen partial pressure, deposition rate, and the like during film formation. The magnetic recording layer 3 is easily oriented in the orientation of the underlayer 2, and can be controlled by the substrate temperature, oxygen partial pressure, deposition rate, and the like. The orientation to be oriented is not particularly limited, but it is more effective to orient the material of the magnetic recording layer 3 so that the axis of easy magnetization is perpendicular to the film surface.

Further, in the present invention, In can be contained in the underlayer 2. That is, the underlayer 2 can be formed of a material represented by the following formula (III).

AB _2-y In _y O ₄ (The conditions of A and B are the same as in the formula (I) and 0 <y ≦ 2.) (III) In this case, only a small amount of In is contained. The lattice constant of the underlayer 2 can be increased, and the relationship between the lattice constants of the underlayer 2 and the magnetic recording layer 3 can be easily controlled.

In the present invention, γ-Fe ₂ O ₃ or Fe ₃ O ₄ can be used as a material of the magnetic recording layer 3 as a material represented by the above formula (II). γ-Fe ₂ O ₃ or Fe ₃ O ₄
When the magnetic recording medium is used, the magnetization becomes large and an appropriate coercive force can be obtained, so that the characteristics are suitable for a perpendicular magnetic recording medium. γ-Fe ₂ O ₃ is different from the formula (II) in molecular formula,
(□ _1/3 Fe ³⁺ _2/3 ) (Fe ₂ ³⁺ ) O ₄ … □ is represented as a vacancy, and the crystal structure is a spinel type, which is a kind of spinel type ferrite. Note that those in which a part of γ-Fe ₂ O ₃ or Fe ₃ O ₄ is replaced by the above-described elements A and B can also be used. In order to prevent abrasion with the magnetic head, as shown in FIG. 2, a structure in which a lubricating layer 4 made of carbon or the like is provided on the surface of the medium may be adopted.

In the present invention, the magnetic recording layer 3 is represented by the following formula (I
V).

Co _z Fe _3-z O ₄ ... (IV) In this case, the inclusion of Co not only increases the magneto-optical effect but also increases the coercive force, which is a characteristic suitable for a magneto-optical recording medium. Note that, in the formula (IV), a compound in which part of Fe is replaced with the above-described elements A and B can also be used.

Further, when the present invention is applied to a magneto-optical recording medium, for example, a layer configuration as illustrated in FIGS. 3 to 8 can be adopted, but the present invention is not limited to this.

FIG. 3 shows the magnetic recording layer 3 having a reflective layer 5 provided on the surface thereof, FIG. 4 shows the magnetic recording layer 3 having a dielectric layer 6 provided between the substrate 1 and the underlayer 2, and FIG. 6, a dielectric layer 6 is provided on the surface of the magnetic recording layer 3 and a dielectric layer 6 is provided on the surface of the magnetic recording layer 3. FIG. FIG. 7 shows the substrate 1
A semi-transmissive reflective layer 5 'and a dielectric layer 6 provided between the magnetic recording layer 3 and the reflective layer 5 on the surface of the magnetic recording layer 3; FIG. In this embodiment, a layer 5 is provided and a protective layer 7 is provided on the surface of the magnetic recording layer 3.

The reflection layer 5, 5 'is a metal film such as Al, Au, Ag, Cu, Cr, or SiO.
_x , Si ₃ N ₄ , AlN, Al ₂ O ₃ , MgO, ZnS, MgF ₂ etc.It is formed from a multilayered film of a dielectric material. In the case of a film, a thickness of about 0.02 to 0.5 μm is appropriate, and in the case of a dielectric multilayer film, each layer needs to be strictly controlled, but the total thickness is generally 0.02 to 1 μm.
The degree is appropriate. The reflectivity of the reflective layers 5, 5 'is not particularly limited, but it is better that the reflective layer 5 on the light incident direction and the reflective side with respect to the magnetic recording layer 3 be higher, and the reflective layer 5' on the light incident side. Needs to be a semi-permeable membrane.

The dielectric layer 6 is made of SiO _x , Si ₃ N ₄ , AlN, Al ₂ O ₃ , MgO, ZnS, M
gF evaporation method using _two such dielectric material, is deposited by sputtering or the like, the film thickness is suitably about 0.05 to 1 [mu] m, in the case of using the multiple reflection effect of the wavelength of light for reading It is necessary to have a predetermined thickness in relation.

The medium of FIGS. 3 to 7 is of a type in which light is incident from the substrate 1 side in magneto-optical recording, whereas the medium of FIG. 8 is of a type in which light is incident from the substrate 1 and the reflection side. Therefore, a thick protective layer 7 is provided on the surface of the magnetic recording layer 3. The protective layer 7 is formed by a coating method using an ultraviolet curing resin, an epoxy resin, or the like, and has a thickness of 0.1 to 2
mm is appropriate.

By providing the reflective layers 5, 5 'and / or the dielectric layer 6 or the protective layer 7 between the substrate 1 and the underlayer 2 and / or on the surface of the magnetic recording layer 3 as described above, the recording sensitivity and the reproduction characteristics are improved. (S / N) can be improved, and it is suitable as a magneto-optical recording medium.

Further, in the present invention, the underlayer 2 may be made of a material represented by the formula (II) so as to have magnetic properties. In this case, the characteristics of the underlayer 2 are preferably those having a high dielectric constant and a low coercive force. In this way, in perpendicular magnetic recording, the magnetic flux of the magnetic head is concentrated during recording,
The power consumption during recording can be reduced and the recording frequency can be improved. In magneto-optical recording, the demagnetizing field of the medium is reduced to reduce the occurrence of reflected magnetism in the recording pits, and the reproduction performance (S / N) Can be improved.

Needless to say, the above-mentioned respective structural features may be arbitrarily combined, and in that case, the respective effects from the respective features are exhibited. Basically, the desired effect can be obtained by one set of the base layer and the recording layer. However, the base layer and the recording layer may be repeatedly laminated for any number of cycles.

〔Example〕

With 1.2mm thick alumino silicate glass as the _{substrate, Ni 0 · 5 Zn 0 ·} 5 In 0 · 5 Fe 1 · 5 O as a base layer on the glass substrate
_{4 A} (100) oriented film, and a Co
An Fe ₂ O ₄ (100) oriented film is formed to a thickness of 0.4 μm and 0.2 μm, respectively, by a facing target sputtering method, and a Cr reflection layer is further formed thereon by an EB evaporation method to a thickness of 0.05 μm. A magneto-optical disk having a configuration as shown in FIG. 3 was manufactured. The lattice constant of the underlayer of this magneto-optical disk is 8.46Å,
The lattice constant of the magnetic recording layer is oriented parallel to the film plane (111)
Converted from the measurement result of the surface, it was 8.34Å.

I tried to evaluate the anisotropy for the magneto-optical disk produced in the above, there is the axis of easy magnetization in the direction perpendicular to the film plane, results in about 300 kJ / m ³ as uniaxial anisotropy energy is obtained, It turned out that it was a perpendicular magnetization film.

Further, no change in magnetic anisotropy was observed even after repeated temperature rise tests and the like. Furthermore, when magneto-optical recording and reproduction were performed on this disk using laser light,
Bits having a width of 1.5 μm were recorded stably, and a reproduction C / N of 45 dB or more was obtained.

As described above, as a base layer, by using a large _{Ni 0 · 5 Zn 0 · 5} In 0 · 5 Fe 1 · 5 O 4 lattice constant than the magnetic recording layer CoFe ₂ O _4, originally uniaxial anisotropy -Free CoFe ₂ O ₄ can be used as a stable perpendicular magnetization film.
By using ₂ O ₄ , the reproduction characteristics as magneto-optical recording could be improved, and further the reproduction characteristics and the recording sensitivity could be improved by the Cr reflection layer.

〔The invention's effect〕

As described above in detail, according to the present invention, the magnetic recording layer can be manufactured at a low temperature, and there is no restriction on the coefficient of thermal expansion of the substrate, so that a general substrate material can be used. Therefore, it is possible to provide a magnetic recording medium at low cost, and furthermore, the perpendicular magnetic anisotropy becomes stable for a long time, and the reliability as a recording medium is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a basic configuration of a magnetic recording medium according to the present invention, FIG. 2 is a cross-sectional view showing a configuration example provided with a lubricating layer, and FIGS. It is sectional drawing which shows the example of a structure at the time of applying to a medium. DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Underlayer 3 ... Magnetic recording layer 4 ... Lubricating layer 5, 5 '... Reflective layer, 6 ... Dielectric layer 7 ... Protective layer

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a base layer formed of a crystalline film having a spinel type crystal structure and a magnetic recording layer formed of a spinel type ferrite crystalline film formed on a substrate in this order. A magnetic recording medium, wherein the lattice constant of the formation is larger than the lattice constant of the magnetic recording layer.