JPS5892B2 - Magnetic recording media for thermal transfer - Google Patents

Description

Detailed Description of the Invention The present invention utilizes the effect that the coercive force of a magnetic material reversibly changes with temperature for mass copying of a metal thin film magnetic recording medium used as a recording magnetic tape. uses cobalt metal, and takes advantage of the decrease in coercive force as temperature rises.The medium, which has a large coercive force at room temperature, is brought into contact with the master tape at high temperature, transferred by applying an appropriate bias magnetic field, and then returned to room temperature. By lowering the temperature, it is possible to provide a magnetic recording medium for thermal copying that is easy to prepare as a slave tape.

Traditionally, the magnetic material for recording magnetic tapes is γ.
Oxides such as Fe2O3 and CrO2 have been used.

These materials are powders, and in order to make magnetic tape, they must be dispersed in a polymeric binder, coated on a polymeric film such as polyethylene terephthalate, and then dried.

In addition, in terms of magnetic properties, the cause of magnetic anisotropy is mainly the shape effect, so the shape anisotropy energy is 2 times the saturation magnetization.
It has the feature that it is proportional to the power.

This fact means that there is almost no temperature change near room temperature.
This is convenient for providing stability as a magnetic tape.

However, when attempting to copy a large amount of signals from a magnetic tape, copying is accomplished by simply contacting the master tape on which the original signal was recorded and applying an appropriate bias magnetic field.

In the case of oxide magnetic materials, the saturation magnetic flux is essentially 5,000 Gauss, which is smaller than that of metals, and therefore the coercive force associated with anisotropy is at most 5,000 e.

For a tape having this level of coercive force, a coercive force of at most 15,000e is sufficient for the master tape, which is 2.5 times or more the coercive force of the slave tape.

Another method is to use thermal residual magnetism generated when the temperature is lowered from above the cue temperature of the ferromagnetic material to below the cue temperature.

Since this method uses the fact that the anisotropic energy becomes almost zero at the Curie point, the coercive force of the master tape does not need to be so large as long as the recording on the master tape is not erased by the bias magnetic field.

As an example of this, for example, CrO2 with a Curie temperature of 120°C
There's a tape.

Another method is to use temperature changes in the anisotropic energy of magnetic materials at room temperature, even if the material has a high coercive force, to lower the holding force during transfer, and use a master tape with a low coercive force as the parent tape. There is also a method of transcription.

The present invention relates to a slave magnetic recording medium for recording, which is used for copying by the third method mentioned above.

The method for obtaining the magnetic recording medium of the present invention will be described below.

Cobalt metal with a purity of 98.5% or higher is used as the starting material, and this is coated with a thin film using known thin film forming techniques such as vacuum evaporation, high frequency sputtering, ion blating, chemical plating, and electroplating. A thin film with a thickness of 1 μm or less is created.

During film formation, the anisotropy is controlled by an oblique incidence deposition method, a deposition method in a magnetic field, or the like in order to control the magnetic anisotropy of the film.

What is particularly important in the structure of the cobalt metal thin film is to orient the six-fold symmetry axis (C axis) of the hexagonal close lattice, which is the main axis of its anisotropy axis.

As an index for evaluating the orientation ratio, the intensity of diffraction lines of X-ray diffraction or electron beam diffraction is used.

In the case of random orientation, the intensity ratio between the (002) plane and the (200) plane is 3=1, but in the cobalt metal thin film used in the present invention, the ratio is 4:1 or higher, which increases the reflection of the (002) plane. Use thick ones.

In a thin film with such C-axis orientation, the anisotropy is larger than that in a randomly oriented cobalt metal thin film, and the magnitude of the anisotropic energy is 0.5X106 to 2.0O.
It has a size of x106er/cm3.

It can be seen that approximately 50% or more of the magnetic anisotropy energy is derived from crystal magnetic anisotropy.

Other causes of anisotropy, such as shape magnetic anisotropy and anisotropy due to the reverse effect of magnetostriction, are also considered, but the sum of these is at most 50%.

As is well known, the magnetocrystalline anisotropy of cobalt metal changes with temperature according to the following equation:

Here, T is the absolute temperature, Kul is the second-order anisotropy constant, and M
s is the saturation magnetization, and Tc is the Curie temperature.

The room temperature is 300°, and the Curie temperature of cobalt is 1388.
It is in °.

At room temperature, T/Tc is approximately 0.2.

As can be seen from the above equation, the anisotropy constant becomes 0 at T=1/3Tc, and as the temperature increases, the anisotropy constant becomes negative.

The cobalt anisotropy constant changes greatly with temperature in this way,
For example, when room temperature (300°K) is 1.0, 4000
It decreases to about 0.5.

This situation is shown in FIG.

The present invention utilizes temperature changes in the anisotropic energy of this cobalt metal thin film.

However, in order for the temperature change to become significant, at least 50% or more of the anisotropic energy must be magnetocrystalline anisotropy.

Specific examples will be described below.

Cobalt (purity 99.9%) was deposited on a 16 μm thick polyethylene terephthalate film substrate using a vacuum deposition method.

At this time, an oblique incidence evaporation method with an incident angle of 60° or more is used, and the evaporation rate is 500 to 1000 λ/sec.

The thin film created has a thickness of 1000 Å.

The coercive force was 8000e at room temperature.

As a result of X-ray diffraction, (002) plane and (200
) surface reflection intensity ratio was 4.5:1.

Figure 2 shows how the coercive force of the thin film changes with temperature.

Further, FIG. 3 shows the change in coercive force with temperature when the coercive force of 3000 is set to 1.0.

Note that the broken line in the figure shows how the magnetocrystalline anisotropy constant of cobalt metal changes with temperature.

In this way, the change in coercive force is similar to the crystal anisotropy of cobalt metal.

Using this magnetic tape, a thermal transfer experiment was conducted using the recording transfer experimental apparatus shown in FIG. 4, and the results shown in the following table were obtained.

In addition, in Fig. 4, 1°2 is a master tape delivery reel and a take-up reel, 3 and 4 are a slave tape delivery reel and a take-up reel, 5 is a temperature-adjustable constant temperature bath, and 6 is a thermostat with adjustable temperature. The bias magnetic field generator 7 is a bias coil.

The bias magnetic field is 45,008 mm, the recording wavelength is 5 μm, and the master tape is made of iron-cobalt alloy powder whose coercive force does not change with temperature, and its coercive force is 180,000 µm.
It is e.

At around room temperature, the bias magnetic field is smaller than the coercive force of the cobalt metal thin film that becomes the slave tape.
A remarkable transfer effect is observed at temperatures above 60°C.

Furthermore, thin film tapes have particularly excellent transfer effects in the short recording wavelength region.

This is because even if the coercive force decreases in the short wavelength region, the thin film makes it difficult for the recorded figure to become blurred due to self-demagnetization. Compared to magnetic recording media, it is possible to increase the output several times in the short wavelength region.

As described above, the magnetic recording medium for thermal transfer of the present invention has various advantages, and its industrial applicability is great.

[Brief explanation of the drawing]

Figure 1 is a temperature change characteristic diagram of the anisotropy constant of cobalt metal.
Figure 2 is a temperature change characteristic diagram of the coercive force of a cobalt metal thin film.
FIG. 3 is a temperature change characteristic diagram of the cobalt metal thin film coercive force and cobalt metal anisotropy constant, and FIG. 4 is a schematic diagram of the recording transfer experimental apparatus.

Claims (1)

[Claims] 1 A cobalt metal thin film is formed by vapor deposition or plating on a polymer molded substrate, and the main part of the anisotropic energy of the cobalt metal thin film is magnetocrystalline anisotropy, and the temperature change rate of coercive force is A magnetic recording medium for thermal transfer, characterized in that the temperature change rate of the magnetocrystalline anisotropy energy of the cobalt metal is similar to that of the cobalt metal.