JPH1092636A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve the output characteristic of a recording medium by forming two oxygen-containing magnetic layers having different crystal systems on a substrate and, at the same time, by making the oxygen concentrations in both magnetic layers maximum at the interfaces of the layers. SOLUTION: A first magnetic layer (lower layer) is formed by supplying an oxygen gas and nitrogen ions to a vapor-depositing area by melting and evaporating Fe in a crucible with the power of an electron gun 5 and, at the same time, introducing the oxygen gas and a nitrogen gas to a gun nozzle 7 and a nitrogen gas to an ion gas while a PET film 2 is run. Then the film 2 is rewound and a second magnetic layer (upper layer) is formed on the first magnetic layer by changing the nitrogen gas introduced to the nozzle 7 to an NH3 gas and the nitrogen gas introduced to the ion gun 3 to an NH3 gas. The oxygen concentrations in both magnetic layers are adjusted so that the concentrations can become maximum at the interfaces of the layers. The lower and upper layers of the film 2, in addition, are respectively constituted of ε-Fe3 N and γ-Fe4 N.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal thin-film type magnetic recording medium having a multilayer magnetic layer made of a material having a different crystal system.

[0002]

2. Description of the Related Art In recent years, magnetic recording is in the direction of high-density recording, and a magnetic recording medium having excellent high-frequency characteristics is demanded. Conventionally, a so-called coating type magnetic recording medium in which magnetic powder is dispersed in an appropriate binder and coated on a support is the mainstream, and various improvements have been made to meet the demand for high-density recording. Is approaching.

A so-called metal thin film type magnetic recording medium having a magnetic layer in which a magnetic metal is adhered to a support by vapor deposition or the like has been developed as a magnetic recording medium which can be expected to have a performance exceeding that of a coating type magnetic recording medium. Metal thin-film type magnetic recording media are considered to be promising for high-density recording because the magnetic layer does not contain a binder and can increase the density of a magnetic material. As the metal thin film type magnetic layer, Co, Co
-Ni, Co-Ni-P, Co-O, Co-Ni-O,
Co-Cr, Co-Ni-Cr and the like have been studied. A vacuum deposition method is most suitable as a manufacturing method when a metal thin film type magnetic recording medium is put into practical use.
Hi8 VTR tapes having a magnetic layer made of i-O and DVC (digital video cassette) tapes having a magnetic layer made of Co-O have already been put to practical use.

[0004]

The above-mentioned metal thin film type magnetic recording medium is desirable in terms of high density recording as compared with the conventional coating type magnetic recording medium, but in the future the recording wavelength will be shorter. Further increase in recording density is expected, and it is considered indispensable to further improve magnetic characteristics, for example, output characteristics, in order to sufficiently cope with this.

[0005]

Means for Solving the Problems In view of the above situation, the present inventors have conducted intensive studies to further improve the output characteristics of a metal thin-film magnetic recording medium, and as a result, have found that a different crystal system is formed on a support. It has been found that this object can be achieved by forming two oxygen-containing magnetic layers having the following formula, and maximizing the oxygen concentration in both magnetic layers at the interface between the two magnetic layers, and completed the present invention. Was.

That is, the present invention relates to a magnetic recording medium having a support, a first magnetic layer formed on the support, and a second magnetic layer formed on the first magnetic layer, Each of the first magnetic layer and the second magnetic layer has a column structure covered with an oxide layer, and a material forming a column of the first magnetic layer and a material forming a column of the second magnetic layer. Another object of the present invention is to provide a magnetic recording medium characterized in that the crystal system is different and that the distribution of the oxygen concentration in the entire magnetic layer is maximum near the interface between the first magnetic layer and the second magnetic layer.

In the present invention, "different crystal systems" means different crystal systems classified according to the characteristics of the crystal axes used as the coordinate system of the crystal. Are included. Normal,
The crystal system is triclinic, monoclinic, orthorhombic, tetragonal,
It is classified into cubic, trigonal, and hexagonal systems.
The “spatial lattice” of the crystal includes a body-centered cubic lattice (bcc) and a face-centered cubic lattice (fccc).
Classification is known. The “crystal structure type” is classified according to the arrangement of atoms in a crystal lattice. Various crystal structure types are known for simple substances and compounds. For example, a spinel structure is known as a typical structure type of the composite oxide. Specifically, the substances constituting the first magnetic layer and the second magnetic layer of the present invention include γ-Fe ₄ N and ε-F
e ₃ N, Fe ₃ O ₄ and the like, a magnetic layer comprising a column of these materials can be easily formed by ion-assisted deposition method as described below.

[0008] In the magnetic recording medium of the present invention, the columns (columnar structure) forming the two magnetic layers are each made of a substance having a different crystal system, and the surface of each column is covered with an oxide layer. It is characterized by. Further, the present invention is characterized in that the distribution of the oxygen concentration in all the magnetic layers is maximized at the interface between the first magnetic layer and the second magnetic layer. That is,
In the present invention, the oxygen concentration in the first magnetic layer is maximum near the second magnetic layer, and the oxygen concentration in the second magnetic layer is maximum near the first magnetic layer. By thus maximizing the oxygen concentration at the interface between the two magnetic layers, the ferromagnetic coupling is weakened, magnetic separation is sufficiently achieved, and the characteristics are improved. In the present invention, the distribution of the oxygen concentration in the magnetic layer does not consider the oxygen concentration near the surface layer (in the direction away from the support) of the second magnetic layer and the vicinity of the support of the first magnetic layer. This is because these portions are easily affected by oxygen derived from the support, the lubricant, the protective layer, and the like, and the oxygen concentration fluctuates significantly. The total oxygen concentration in each of the first magnetic layer and the second magnetic layer is not limited. However, in the case of a magnetic layer other than iron oxide, the total oxygen concentration is preferably 5 to 25 atomic%, more preferably 7 to 20 atomic%.

In the present invention, the crystal system of the substance forming the magnetic layer is determined by electron diffraction, electron probe microanalysis (E
PMA) and TEM photographs. The amount of the oxide layer can be determined by EPMA or Auger electron spectroscopy in the depth direction.

In the present invention, the magnetic layer is preferably formed by so-called oblique evaporation.

Further, the magnetic recording medium of the present invention may have three or more magnetic layers. When three or more magnetic layers are formed, the two layers farthest from the support need to be the first magnetic layer and the second magnetic layer of the present invention. In this case, the crystal system and oxygen concentration of the magnetic layers other than the first magnetic layer and the second magnetic layer are not limited, but the first magnetic layer and the second magnetic layer are formed by columns covered with an oxide layer like the second magnetic layer. Is more desirable.

In the present invention, as described above, two magnetic layers are formed by columns of substances having different crystal systems, and the oxygen concentration in the magnetic layers is maximized at the interface between the two magnetic layers, whereby the characteristics are improved. Although the reason for the improvement is not clear, it is considered that sufficient magnetic separation is achieved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the magnetic recording medium of the present invention,
The first magnetic layer and the second magnetic layer described above can be formed, for example, by depositing a magnetic metal (simple or alloy) on a support. Further, at the time of vapor deposition, it can also be formed by a so-called ion-assisted vapor deposition method in which nitrogen ions, carbon ions, and oxygen ions are appropriately supplied. Further, the oxide layer on the column surface can be formed by supplying oxygen gas during vapor deposition. The distribution of the oxygen concentration can be adjusted by adjusting the position where the oxygen gas is introduced, the amount of the introduced oxygen gas, the position of the metal material (evaporation source) at the time of vapor deposition, the position of the shielding plate, and the like.

In the present invention, the thicknesses of the first magnetic layer and the second magnetic layer are not limited, but are usually 200 to 200, respectively.
0 °. When three or more magnetic layers are formed, the thickness of the entire magnetic layer is about 500 to 4000 °.

Examples of the material of the support of the magnetic recording medium of the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; polycarbonate; Plastics such as vinyl; polyimide; and aromatic polyamide are used. The thickness of these substrates is about 3 to 50 μm.

On the second magnetic layer (the outermost magnetic layer), a protective layer having a thickness of about 10 to 200 °, especially a carbon thin film such as diamond-like carbon or graphite, or a silicon-containing material such as silicon oxide or silicon carbide. It is desirable to provide a protective layer made of a thin film, a zirconium oxide thin film, or the like. Further, it is preferable to form a lubricating layer having a thickness of about 2 to 50 °, particularly a lubricating layer made of a fluorine-based lubricant such as perfluoropolyether, on the magnetic layer or the protective layer. Further, on the surface opposite to the surface on which the magnetic layer is formed, a back coat layer or the like containing carbon black as a main component and having a thickness of about 0.1 to 1.0 μm may be further provided. As a raw material for forming these layers, conventionally known materials can be appropriately used. Alternatively, a metal such as a Cu-Al alloy may be deposited to form a back coat layer having a thickness of about 500 to 10000 °.

FIG. 1 shows an example of a method for manufacturing a magnetic recording medium according to the present invention. FIG. 1 shows a main part of an ion-assisted vapor deposition apparatus, which is an apparatus for forming a magnetic layer made of a Fe-N-based material. In FIG. 1, 1 is a can roll, 2 is a base film, 3 is an ion gun, 4 is a shielding plate, 5 is an electron gun, and 6 is a crucible, which contains metallic iron. Reference numeral 7 denotes a gas nozzle. The components other than the ion gun 3 are housed in a vacuum vessel (not shown). The base film 2 is transported on a cylindrical can roll 1. Further, a crucible 6 made of MgO is placed below the can roll 1, and iron (for example, Fe having a purity of 99.95%) is accommodated in the crucible 6. Is irradiated with an electron beam. As a result, Fe is vaporized by heating and adheres to the base film 2 running on the can roll 1.
On the other hand, during the deposition of Fe, the ion gun 3 is disposed so that ions are irradiated in a direction perpendicular to the deposition surface of the film 2, and a gas serving as a nitrogen source, for example, a nitrogen gas is supplied to the ion gun 3. Ions are generated and supplied into the deposition area. Thereby, the magnetic layer of the present invention mainly containing Fe and containing nitrogen is formed. The crystal system of this substance can be known by analyzing the formed magnetic layer by electron beam diffraction as described above. Further, in order to oxidize the columns of the magnetic layer, oxygen gas is supplied to the deposition region by the gas nozzle 7. This forms a first magnetic layer in which the columns are covered with the oxide layer. The second magnetic layer may be formed on the first magnetic layer in the same manner. The first magnetic layer and the second magnetic layer may be formed continuously using an apparatus as shown in FIG. 1 or may be formed by repeating vapor deposition.

In the present invention, it is more preferable that the first magnetic layer (lower layer) is formed of Fe ₃ N and the second magnetic layer (upper layer) is formed of Fe ₄ N. In this case, it can be formed while introducing oxygen by the apparatus of FIG. 1 as described above. Both are Fe-N-based materials, and are more preferable in terms of the manufacturing process and magnetic properties. Thus, the first magnetic layer is F
FIG. 2 schematically shows a magnetic recording medium of the present invention in which e ₃ N and the second magnetic layer are formed of Fe ₄ N, and columns of both magnetic layers are covered with an oxide layer. In FIG. 2, 21 is a first magnetic layer, 22 is a second magnetic layer, 23 is a column of Fe ₃ N,
Is a column of Fe ₄ N, and 25 is a base film.

[0019]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 (1) Production of Magnetic Tape A PET film having a thickness of 6.3 μm was set in the apparatus shown in FIG. 1, the film was run at 2.5 m / min, and the power of the electron gun 5 was set to 20 kW in a crucible. Is melted and evaporated, and at the same time, oxygen gas and nitrogen gas
At 0 SCCM, nitrogen gas was introduced into the ion gun 3 at 20 SCCM, and oxygen gas and nitrogen ions were supplied to the deposition region.
The acceleration voltage of the ion gun 3 was 250 V. Under these conditions, a first magnetic layer (lower layer) was formed at 600 °. Subsequently, the film was rewound, and the gas introduced into the gas nozzle 7 was 7 SCCM of oxygen gas and 10 SCCM of NH ₃ gas, the gas introduced into the ion gun 3 was 15 SCCM of NH ₃ gas, and the acceleration voltage of the ion gun 3 was 120 V. A second magnetic layer (upper layer) was formed on the first magnetic layer at a thickness of 1150 °.

Next, a protective layer made of a diamond-like carbon thin film having a thickness of 85 ° was formed on the second magnetic layer by ECR plasma CVD using benzene as a carbon source. Further, a perfluoropolyether having a polar group -OH group on this protective layer [DEMIN S:
A] was applied to a thickness of 20 ° to form a lubricating layer. A back coat layer was formed on the surface of the film opposite to the surface on which the magnetic layer was formed. The back coat layer is 2
A binder containing carbon having a diameter of 0 to 30 nm was applied to a film such that the thickness after drying became 0.5 μm, and the film was dried.

The first and second magnetic layers obtained as described above,
The film on which the diamond-like carbon protective layer, the fluorine-based lubricating layer and the back coat layer were formed was cut into a width of 8 mm, and was loaded on a cassette case to obtain an 8 mm video tape. In the magnetic layer of the film cut into 8 mm, electron beam diffraction by a cross-sectional TEM sample showed that the lower layer was ε-Fe ₃ N and the upper layer was γ-Fe ₄ N.

(2) Performance Evaluation The isolated waveform and output of the 8 mm video tape obtained above were evaluated by the following methods. Table 1 shows the results. Isolated Waveform The isolated waveform was obtained by recording a signal (A) having a waveform as shown in FIG. 3A and evaluating the shape of the reproduced signal. That is, FIG.
The area of the hatched portion S of the reproduced signal (B) was calculated as described above, and the relative evaluation was made when Comparative Example 2 was set to 100%. this%
The smaller the value, the better the isolated waveform. The output is output using a modified 8mm VTR.
Outputs at 1, 5, 10, and 20 MHz were measured. The output was a relative evaluation using Comparative Example 2 as a reference (0 dB).

The Auger profile of the magnetic tape obtained in Example 1 (measurement conditions: electron gun; acceleration voltage 10
kV, emission current 10 nA, magnification 2000 times, etching conditions: etching gas is argon, acceleration voltage 3
kV, ion current 300 nA, etching every 30 seconds)
Is shown in FIG. From this Auger profile, it can be seen that the oxygen concentration is maximum near the interface between the first magnetic layer and the second magnetic layer.

Example 2 In Example 1, 35 SCCM of oxygen gas was introduced into the gas nozzle 7 at the time of forming the first magnetic layer (lower layer), and oxygen gas was also supplied to the ion gun 3 instead of NH ₃ gas at 40 SCC.
A magnetic layer was formed in the same manner as in Example 1 except that M was introduced, and an 8 mm video tape was obtained. The thickness of the magnetic layer formed in this example was 500 ° for the first magnetic layer (lower layer) and 1250 ° for the second magnetic layer (upper layer). The same evaluation as in Example 1 was performed using the obtained 8 mm video tape. Table 1 shows the results. Auger profile of the magnetic tape obtained in Example 2 (measurement conditions are the same as in Example 1)
Is shown in FIG. From this Auger profile, it can be seen that the oxygen concentration is maximum near the interface between the first magnetic layer and the second magnetic layer.

Example 3 On the first magnetic layer (lower layer) obtained in Example 1,
Second magnetic layer (upper layer) having the same composition as the first magnetic layer of Example 2
Was formed. However, the thickness of the upper layer was 550 °, and the thickness of the lower layer was 1270 °. Others are the same as in the first embodiment.
mm videotape was obtained. The same evaluation as in Example 1 was performed using the obtained 8 mm video tape. Table 1 shows the results.

Comparative Example 1 On the first magnetic layer (lower layer) obtained in Example 1,
A magnetic layer having the same composition as the first magnetic layer was formed and used as a second magnetic layer (upper layer). However, the thickness of the lower layer was 650 °, and the thickness of the upper layer was 1120 °. Otherwise, an 8 mm video tape was obtained in the same manner as in Example 1. The same evaluation as in Example 1 was performed using the obtained 8 mm video tape. Table 1 shows the results.

Comparative Example 2 A single magnetic layer was formed in the same manner as in the formation of the second magnetic layer in Example 1. However, the introduction amount of oxygen gas to the gas nozzle 7 was 13 SCCM, and the introduction amount of NH ₃ gas was 12 SCCM.
And the amount of NH ₃ gas introduced into the ion gun 3 is 18 SC
CM. The thickness of this magnetic layer was 1800 °.
Otherwise, an 8 mm video tape was obtained in the same manner as in Example 1. The same evaluation as in Example 1 was performed using the obtained 8 mm video tape. Table 1 shows the results.

[0029]

[Table 1]

[0030]

According to the present invention, a metal thin film type magnetic recording medium having excellent magnetic characteristics, particularly excellent output characteristics, can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a main part of a vapor deposition apparatus for manufacturing a magnetic recording medium of the present invention.

FIG. 2 is a schematic view showing the structure of a magnetic recording medium according to the present invention.

FIG. 3 is a schematic diagram showing a method for measuring an isolated waveform.

FIG. 4 is an Auger profile of a magnetic tape obtained in Example 1.

FIG. 5 is an Auger profile of a magnetic tape obtained in Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Can roll 2 Base film 3 Ion gun 4 Shield plate 5 Electron gun 6 Crucible 7 Gas nozzle

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hirohide Mizunoya 2606 Kabane-cho, Akaga, Tochigi Pref.Katsumi Endo 2606 Kaiga-cho, Akabane, Haga-gun, Tochigi

Claims (2)

[Claims] 1. A magnetic recording medium comprising a support, a first magnetic layer formed on the support, and a second magnetic layer formed on the first magnetic layer, wherein Both the magnetic layer and the second magnetic layer have a column structure covered with an oxide layer,
In addition, the crystal system of the material constituting the column of the first magnetic layer and the material constituting the column of the second magnetic layer are different, and furthermore, the distribution of oxygen concentration in the entire magnetic layer is different from that of the first magnetic layer and the second magnetic layer. A magnetic recording medium having a maximum near an interface between layers. 2. The magnetic recording medium according to claim 1, wherein said first magnetic layer is made of Fe ₃ N, and said second magnetic layer is made of Fe ₄ N.