JPH0614404B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a so-called ferromagnetic metal thin film type magnetic recording medium such as a vapor deposition tape.

[Outline of Invention]

The present invention secures a high coercive force by using a Co—Pt-based alloy containing an inert gas as an alloy material forming the metal magnetic thin film in a magnetic recording medium having a metal magnetic thin film formed as a magnetic layer. The purpose of the present invention is to provide a magnetic recording medium which is free from curl and which enables high-density magnetic recording by eliminating the strain due to the tensile stress of the metal magnetic thin film by forming a carbon protective film.

[Conventional technology]

In the field of magnetic recording, the density of recording signals and the wavelength thereof have been shortened, and in response to this, magnetic recording media having high coercive force Hc and residual magnetic flux density Br have been demanded.

Therefore, in response to this, a magnetic thin film made of a ferromagnetic metal material is directly deposited on a non-magnetic support such as a polyester film by a means such as a vacuum deposition method or a sputtering method, and this is used as a magnetic layer. A ferromagnetic metal thin film type magnetic recording medium has been proposed and attracted attention. In the magnetic recording medium of this ferromagnetic metal thin film, not only the coercive force Hc and the residual magnetic flux density Br are high, but also the thickness of the magnetic layer can be made extremely thin, so that the recording demagnetization and the thickness loss during reproduction are extremely small. Since there is no need to mix a resin binder such as a vinyl chloride-vinyl acetate-based copolymer or polyurethane resin with, it is possible to dramatically increase the packing density of magnetic materials, which has many advantages in terms of magnetic properties. is doing.

However, in this type of magnetic recording medium, since the vacuum thin film forming technique is used as a means for forming the above-mentioned magnetic thin film, the base film, which is a non-magnetic support, is easily thermally damaged, When the vaporized metal atoms are recrystallized into a thin film and contracted, internal stress is generated, and as a result, a concave bend called curl occurs especially when a flexible non-magnetic support is used. have.

For example, when a hard substrate such as Al, Cu, glass, or ceramics is used in manufacturing a magnetic recording medium, even if a magnetic thin film is formed on the surface, the original shape is hardly changed and the distortion is extremely high. Few. On the other hand, when a flexible material such as a polymer film such as polyethylene terephthalate or a polyimide film is used as the substrate,
When the magnetic thin film is formed on the surface, distortion is caused by the internal stress of the magnetic thin film itself or the thermal stress generated by the difference in the coefficient of thermal expansion between the substrate and the magnetic thin film.

[Problems to be solved by the invention]

When such distortion occurs and curl occurs, it has adverse effects such as spacing loss and output fluctuation during recording and reproduction.

Therefore, the present invention provides a magnetic recording medium that can eliminate strain without performing heat treatment or mechanical treatment after forming a magnetic thin film, has high coercive force without curling, and is suitable for high-density recording. With the goal.

[Means for solving problems]

The present inventor, as a result of earnest research over a long period of time without achieving the above-mentioned object, relaxes the tensile stress of the magnetic thin film itself by including an inert gas in the film, and further provides a carbon protective film, We succeeded in eliminating the strain by balancing the compressive stress and the tensile stress of the magnetic thin film.

The present invention, which has been completed based on such findings, on a nonmagnetic _{support, (Co 1-xy Fe x} Ni y) 1-Z Pt z ( however, 0 ≦ x ≦ 0.03, 0 ≦ y ≦ 0.3, 0 <z ≦ 0.
45), wherein a magnetic thin film having a composition shown in 45) and containing an inert gas is formed, and a carbon protective film is formed on the magnetic thin film.

[Action]

Thus, as the alloy material of the magnetic thin film _{(Co 1-xy Fe x Ni} y) 1-Z Pt z ( however, 0 ≦ x ≦ 0.03,0 ≦ y ≦ 0.3,0 <z ≦ 0.
A large coercive force is generated by using the composition represented by 45) and incorporating an element of an inert gas in the film. Further, the introduction of this inert gas also exerts an effect of relaxing strain of the magnetic recording medium, and by providing a carbon protective film, compressive stress acts and the strain can be zero.
The curl is eliminated.

〔Example〕

 Hereinafter, the present invention will be described in detail.

In the present invention, a Co—Pt-based alloy having a high coercive force, a high squareness ratio, and a high corrosion resistance is used as an alloy material forming the magnetic thin film that is the magnetic layer.

It is generally known that a Co—Pt-based alloy film becomes a magnetic film having a high coercive force and a high squareness ratio when manufactured by a sputtering method. However, the film forming method by the sputtering method has a low film forming speed and has a problem in mass productivity. Therefore, a vacuum evaporation method having a high film forming speed (in this case,
Since Co and Pt have quite different vapor pressures, it is preferable to use a vapor deposition method by dual source evaporation. However, the film thus formed by the vacuum evaporation method has a drawback that the coercive force is small. When the inventor pursued this cause,
It was found that this was because Co and Pt were not completely alloyed, the crystal structure was uniform, and the columnar structure was not clear.

Therefore, the present inventor repeated experiments for producing a Co—Pt-based alloy film having a high coercive force by a vacuum deposition method,
We have come to the conclusion that a film with a high coercive force can be produced by incorporating an inert element into the film by vacuum vapor deposition in an inert gas atmosphere.

For example, Pt by vacuum deposition without introducing nitrogen gas
When a Co—Pt alloy film was produced by changing the content of
As shown by the curve c in FIG. 1, the coercive force is 300 at maximum.
It was about Oersted. On the other hand, nitrogen gas was introduced and the partial pressure was adjusted to 4 × 10 ⁻⁴ Torr or 7 × 10 ^4.
-4 Torr, a Co-Pt alloy film was prepared by a vacuum deposition method. As shown in the curve a or curve b in FIG. 1, the coercive force was the largest when the Pt content was about 25 atomic%. It turns out that the former reaches 1500 Oersted and the latter reaches 2000 Oersted. The film thickness is 1000Å. From this, it is understood that the introduction of nitrogen gas has a great influence on the coercive force in the production of the Co—Pt film by the vacuum deposition method.

Further, when a similar experiment was attempted with Ar gas in addition to nitrogen gas, the effect was slightly small when compared with the same gas partial pressure, but it was within a practical range. In addition, nitrogen, A
In addition to r, He, Ne, Kr, Xe, Co _{2 and the} like also have similar effects.

The details of the mechanism by which the coercive force is increased by the introduction of the above-mentioned inert gas are unknown, but it is presumed that the reason is as follows. That is, Co and Pt are scattered and mixed by introducing an inert gas by a vacuum deposition method,
Fully alloy. As a result, two phases are formed in the Co-Pt alloy phase. This phase is composed of a regular phase and an irregular phase, and the energy generated by the domain wall is greatly different between the two phases. This is the main reason why the coercive force increases.
Further, it is conceivable that the coercive force is increased due to the effect that the columnar structure is clarified by introducing the inert gas and the movement of the domain wall is hindered by the grain boundary.

On the other hand, it can be seen from FIG. 1 that the coercive force rather decreases when the Pt content is too large, and it can be said that it is preferable to suppress the Pt content to 45 atomic% or less.

Also, by adding a small amount of Fe to the Co-Pt-based alloy, a high coercive force and a squareness ratio can be realized, and the magnetic flux density can be increased.

The present inventor manufactured a Co—Pt—Fe film using a vacuum vapor deposition apparatus as shown in FIG. 2 in order to investigate the effect of adding Fe.

Figure 2 shows the vacuum evaporation system used in this experiment. The polymer film substrate (1) is continuously moved from the unwinding roll (2) to the winding roll (3). C
An o-Pt-Fe film was deposited. An electron beam impact method was used for melting the metal. Since Co-Fe and Pt have large vapor pressures, a two-source vapor deposition method using a Co-Fe evaporation source (4) and a Pt evaporation source (5) was used. In addition, nitrogen gas was introduced as an inert gas during vapor deposition.

In this experiment, the degree of vacuum before heating the evaporation source was set to 2 × 10 ^-6
Torr or less, and the inert gas partial pressure during vapor deposition is 7 × 10 ^-4 To
It was rr. The evaporation amount of Co-Fe and Pt is automatically controlled through the film thickness monitor heads (6) and (7) near the evaporation sources (4) and (5), respectively. The film composition of Pt and Pt can be freely changed. Further, the film thickness of the substrate (1) can be changed by the evaporation amount and the moving speed of the substrate (1).

Using the above-mentioned device, a magnetic thin film (film thickness 500Å) having a composition of (Co _1-x Fe _x ) _0.9 Pt _0.1 was formed and the magnetic characteristics were examined. FIG. 3 is a characteristic diagram showing the relationship between the amount x of Fe and the coercive force Hc, and FIG. 4 is a characteristic diagram showing the relationship between the amount x of Fe and the squareness ratio.

From these drawings, the coercive force Hc and the squareness ratio of the (Co _1-x Fe _x ) _0.9 Pt _0.1 film become maximum at x = 0.01. x>
At 0.01, the coercive force and the squareness ratio decrease from the maximum values,
In the range of x ≦ 0.03, both the coercive force and the squareness ratio are larger than Co _0.9 Pt _0.1 . Therefore, in the range of x ≦ 0.03, Co
If Fe is added to, the magnetic characteristics will be improved.

In the above example, the result by the vacuum evaporation method is shown, but the same effect can be obtained by adding Fe to Co by the sputtering method.

It was also found that the addition of Fe has an effect on the magnetic flux density, and that the saturation magnetic flux density increases as the Fe content increases.

There are various possible causes for the effect of the addition of the Fe element, and one of the causes is considered to be the phase transition of the Fe—Co type crystal type. In the Fe-Co system, the anisotropy (K _u1 ) initially increases with the addition of Fe, but 1.04
This anisotropy decreases discontinuously at around atomic%, and K _u1 = −
It shows a large negative value of 10.2 × 10 ⁶ erg / cc. This is because the crystal type is changed here and the close-packed hexagonal lattice is changed to the double hexagonal lattice. When the anisotropy increases or the crystal type changes and the easy axis direction increases in this way, the coercive force and the squareness ratio are expected to improve. In the case of the present invention, it is a thin film, and the crystal structure of the entire film does not change, but a part of the film undergoes a metastable phase transition, and the crystal form changes from a close-packed hexagonal lattice to a double hexagonal lattice. It was revealed by electron diffraction that the changes were made.

As described above, it was found that the addition of Fe was effective in improving the magnetic characteristics of the Co—Pt-based alloy thin film.
It was also found that the addition of is effective in improving the squareness ratio.

For example, when the relationship between the addition amount x of Ni and the squareness ratio was examined with (Co _1-x Ni _x ) _0.8 Pt _0.2, as shown in FIG. 5, the squareness ratio tends to increase as the Ni amount increases. I knew it was.

However, the addition of Ni brings about a decrease in coercive force, so C
It is preferable to limit the content to 30 atomic% with respect to o.

From this point of view, as the composition of the Co-Pt system alloy used as a magnetic thin film in the present _{invention, (Co 1-xy Fe x} Ni y) 1-Z Pt z ( however, 0 ≦ x ≦ 0.03,0 ≦ y ≦ 0.3, 0 <z ≦ 0.
It is desirable to set it to 45).

The above Co—Pt-based alloy is deposited on a non-magnetic support to form a magnetic layer. Here, as the material of the non-magnetic support, polyesters such as polyethylene terephthalate,
Polyolefins such as polyethylene and polypropylene,
Cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, and plastics such as polycarbonate, polyimide and polyamideimide are used. The form of the non-magnetic support may be a film, tape, sheet,
It may be a disc, card, drum or the like.

Generally, when a magnetic thin film as described above is deposited on a non-magnetic support typified by such a polymer film by a method such as vacuum deposition or sputtering, distortion occurs in the non-magnetic support, Curling occurs.

However, in the present invention, since the magnetic thin film contains an inert gas as an impurity, the strain is relaxed and the curl amount is reduced.

For example, when the relationship between the Ar gas partial pressure and the curl amount δ during vapor deposition was examined for a Co _0.8 Pt _0.2 film, the curl amount δ decreases as the Ar gas partial pressure increases, as shown in FIG. It became clear. The curl amount δ is
As shown in FIG. 7, the obtained magnetic recording medium was 4 cm × 1
It was cut into a strip of cm, and the distance from the reference plane to the tip of the substrate was measured δ. It is considered that the curl amount δ becomes small because the compressive stress is induced by containing an inert gas as an impurity in the Co—Pt film.

Of course, the introduction of the above-mentioned inert gas is also effective in terms of coercive force, and as shown in FIG. 8, the coercive force also increases as the Ar gas partial pressure increases.

Thus, the introduction of the inert element into the magnetic thin film has an effect in terms of magnetic characteristics and strain relaxation, but this alone does not completely reduce the curl amount δ, but completely eliminates the curl. It is necessary to use other means together.

In order to further reduce the strain (curl), a film having a compressive stress may be formed on the magnetic thin film. There are various films having compressive stress, but from the viewpoint of a magnetic recording medium, it is preferable that the film is as thin as possible, and that the magnetic thin film can be protected and the running property can be improved.

From such a viewpoint, as a result of repeated studies, it was found that the carbon protective film is optimal.

FIG. 9 shows the relationship between the thickness of the carbon protective film and the curl amount δ. From FIG. 9, it can be seen that when the carbon protective film is applied, distortion occurs on the side opposite to that when the magnetic thin film is applied. Therefore, the curl of the magnetic recording medium can be eliminated by providing the carbon protective film with a film thickness such that the curl amount of the magnetic thin film containing the above-mentioned inert gas cancels the curl amount of the magnetic thin film.

The carbon protective film has excellent lubricity and corrosion resistance, and is usually formed by a method such as a vacuum deposition method or a sputtering method.

For example, when the vacuum deposition method is used, the pressure is 5 × 10 ⁻⁵ To.
A vacuum degree of rr or less and a substrate temperature of 50 to 250 ° C. may be used, and as a heating method, an electron beam heating method, a resistance heating method, an induction heating method, an arc discharge method, or the like is used.

When the sputtering method is used, an inert gas such as Ar is introduced, a pressure of 1 × 10 ⁻² to 1 × 10 ⁻³ Torr vacuum degree and a substrate temperature of 50 to 250 ° C. are used as a target of a carbon plate. (Thickness of about 1 to 4 mm) may be used and RF power of 1 to 10 kW or DC power of 500 W to 10 kW may be applied.

From the above results, a Co _0.8 Pt _0.2 film as a magnetic thin film having a film thickness of 80 was formed on a polyimide film having a thickness of 20 μm in an Ar gas atmosphere at a substrate temperature of 50 ° C. and 6 × 10 ⁻⁴ Torr.
Formed with 0Å. Further, a carbon protective film having a film thickness of 250Å was formed on the magnetic thin film.

The magnetic recording medium thus obtained has a coercive force of 10
It showed excellent magnetic properties of 00 Oersteds and a squareness ratio of 0.87 and almost no curl. Further, when the durability of this magnetic recording medium was examined, sufficient characteristics could be obtained by a still test (continuous 1 million passes) using a magnetic head.

〔The invention's effect〕

As is clear from the above description, in the present invention,
Co-Pt containing an inert gas as the material of the magnetic thin film
Since the carbon-based protective film is provided on the magnetic thin film by using the system alloy, the distortion that causes the curl is eliminated, and the magnetic recording medium without the curl, the output fluctuation and the spacing loss can be obtained.

Further, the introduction of the inert gas increases the coercive force and the squareness ratio of the magnetic thin film, which is suitable for high density recording.

Further, the magnetic thin film is protected by the action of the carbon protective film, and the magnetic recording medium is excellent in running property, durability and corrosion resistance.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the Pt content and the coercive force Hc when nitrogen is introduced as an inert gas during the production of the Co—Pt film. FIG. 2 is a schematic configuration diagram showing an example of a vacuum vapor deposition apparatus for producing a Co—Fe—Pt thin film. FIG. 3 is a characteristic diagram showing the relationship between the Fe amount x and the coercive force Hc in the Co—Fe—Pt thin film, and FIG. 4 is a characteristic diagram showing the relationship between the Fe amount x and the squareness ratio. FIG. 5 is a characteristic diagram showing the relationship between the amount of Ni added and the squareness ratio in the Co—Pt thin film. FIG. 6 is a characteristic diagram showing the relationship between the Ar gas partial pressure and the curl amount when forming a Co—Pt thin film, and FIG. 7 is a schematic diagram for explaining the curl amount. FIG. 8 is a characteristic diagram showing the relationship between the partial pressure of Ar gas and the coercive force when forming a Co—Pt thin film. FIG. 9 is a characteristic diagram showing the relationship between the thickness of the carbon protective film and the curl amount.

Claims (1)

[Claims] 1. A (Co _1-xy Fe _x Ni _y ) _1-Z Pt _z (where 0 ≦ x ≦ 0.03, 0 ≦ y ≦ 0.3, 0 <z ≦ is formed on a non-magnetic support. 0.
45) A magnetic recording medium comprising a magnetic thin film having a composition shown in 45) and containing an inert gas, and forming a carbon protective film on the magnetic thin film.