JPS5931764B2 - Jikikirokuhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for magnetically recording signals on a magnetic recording medium using MnBi alloy magnetic powder as a recording element.

MnBi alloy magnetic powder has a high coercive force of 10,000 Oe or more at room temperature, and has the advantage that once it is magnetized, it is hardly demagnetized by a normal external magnetic field. However, it is very difficult to perform magnetic recording on magnetic recording bodies using such magnetic powders with high coercive force as recording elements at room temperature, and a special magnetic recording device that provides a strong magnetic field is required. Therefore, this invention
A normal magnetic recording device (magnetic field of about 200 to 4000 oersteds) is applied to a magnetic recording body using i-alloy magnetic powder as a recording element.
The purpose of this invention is to provide a new magnetic recording method that allows recording.

The present invention will be explained below based on the drawings.

It is expressed as HC=2/Is-4π-s [here: crystal anisotropy constant, Is: saturation magnetization], and according to calculations, a temperature characteristic curve shown by the broken line curve in FIG. 1 is drawn.

Since the coercive force (HC) becomes zero at 170° in this broken line curve, the demagnetizing field (4π engineering s) is larger than the crystal anisotropy magnetic field (2/Is) at temperatures lower than the above temperature. , 170°, the axis of easy magnetization tilts from the C-axis direction, which is the same direction as the applied magnetic field, to the C-plane direction (see FIG. 3). In other words, even if the magnetization direction is in the C-axis direction when a magnetic field is applied on the low-temperature side due to 170 degrees, when the magnetic field is returned to zero, it tilts toward the C-plane direction, and due to this, the residual magnetization decreases rapidly. It seems that it will. This phenomenon becomes even more obvious at lower temperatures,
As shown in Figure 2, below 150°, the squareness ratio is 0.
The residual magnetization is as low as 4 or less. The above fact is 200°
Below that, the coercive force becomes small, so even if it is possible to magnetize with a normal magnetic recording device, if the temperature is too low, the required residual magnetization cannot be obtained, and instantaneous magnetic recording using a pulsed magnetic field will not be able to reproduce it. This shows that magnetic recording with large output is difficult. Therefore, if magnetic recording is to be performed at, for example, liquid nitrogen temperature (approximately 80 K), it is necessary to return the temperature from the above temperature to room temperature while applying a magnetic field, and such operations are troublesome. Figure 4 shows the ratio of remanent magnetization to remanent magnetization (assumed to be 100) when a high magnetic field is applied to achieve saturation remanence, that is, saturation magnetization, when magnetic recording is actually performed on the magnetic recording medium in a magnetic field of 4000 oersteds. It is something.

As is clear from this figure, the ratio of residual magnetization to saturation residual magnetization shows a high value of 80 to 100 at 150 to 2000K, and it decreases extremely even below 1500K and above 200K. .

This is because at temperatures higher than 2000K, the coercive force is large, so a weak magnetic field at 4000 degrees cannot sufficiently magnetize, while at temperatures lower than 1500K, the residual magnetization becomes too small, resulting in a squareness ratio of 0. This shows that instantaneous normal magnetic recording using a pulsed magnetic field is possible in the low temperature range of 150 to 2000 K where residual magnetization of 4 or more is obtained. This invention was made based on the above knowledge. In other words, a magnetic recording body using MnBi alloy magnetic powder as a recording element can be instantly recorded by a normal magnetic recording device by cooling it to a specific temperature range of 150 to 2000K. can be magnetically recorded, and its playback output is also large.

Mn of the MnBi alloy magnetic powder applicable to this invention,!
l:. The atomic ratio of Bi is Mn/Bi6/4 to 5, as is clear from the relationship with the saturation magnetization shown in FIG.
Since the saturation magnetization shows the maximum amount in the range of /5 and decreases on both sides thereof, it is preferably in the range of about 8/2 to 4/6.

Further, the particle size may be appropriately determined depending on the type of magnetic recording medium, and a particle size of about 10 μm or less is usually used. Next, the present invention will be specifically explained with reference to Examples. Example MnBi alloy magnetic powder (atomic ratio Mn/Bi-6/4
, particle size of approximately 0.5 μm, coercive force at room temperature of approximately 16,000 oersted), 100 parts by weight, VAGH (Vinyl chloride mono-vinyl acetate copolymer manufactured by V.C.C. Co., Ltd., trade name), 30 parts by weight, dioctyl J oxide A composition consisting of 5 parts by weight, 200 parts by weight of methyl isobutyl ketone, and 200 parts by weight of toluene was kneaded in a ball mill to prepare a magnetic paint, and this paint was applied to a thickness of about 10 μm on a 20 μm thick polyester base film and dried. to create magnetic recording tape.

The thus obtained magnetic recording tape is pasted on a card-like substrate to make a magnetic card, which has a
The sample was cooled to 00K and a constant signal was recorded using a conventional magnetic recording device.

The table below shows the results of reproducing signals from this magnetic card with a reproducing device and the results of measuring the reproduction output again after placing a permanent magnet on the magnetic card and placing it in a strong magnetic field.

For comparison, the same table also shows the results of magnetic recording at room temperature on a magnetic card obtained by using a normal CO-containing iron oxide magnetic powder as a magnetic alloy powder. As is clear from the above table, according to the method of the present invention, a predetermined signal is appropriately magnetically recorded, and a reproduction output that is not significantly different from that of the comparative example can be obtained.

Furthermore, when an external magnetic field is applied, the comparative example is almost erased and has a reproduction output of -40 dB, whereas the one according to the invention method has a reproduction output of -1 dB or more and is hardly erased. As can be seen from the figure, the MnBi alloy magnetic powder can take full advantage of its extremely high coercive force at room temperature.

[Brief explanation of drawings]

Figures 1, 2, and 4 are temperature characteristic diagrams of the coercive force, squareness ratio, and ratio of residual magnetization to saturated residual magnetization of a magnetic recording medium using MnBi alloy magnetic powder as a recording element, respectively;
FIG. 3 is an explanatory diagram showing the magnetization direction of the MnBi alloy magnetic powder, and FIG. 5 is a diagram showing the relationship between the atomic ratio and the saturation magnetization of the MnBi alloy magnetic powder.

Claims (1)

[Claims] 1. A magnetic recording method, characterized in that magnetic recording is performed by cooling a magnetic recording body using MnBi alloy magnetic powder as a recording element to 150 to 200°K.