JPS6295703A - Magnetism erasing method - Google Patents

Abstract

PURPOSE:To record residual noise and distortion factor by acting a magnetic field whose residual magnetization direction along the recording face is inverted at the surface layer and the deep layer beneath the surface layer. CONSTITUTION:Permanent magnets 10, 11 are directed to the recording face 6 and arranged with an interval in the relative moving direction 12 with a magnetic recording medium 1. The polarity of the succeeding magnet 11 is opposite to that of the preceding magnet 10, the deep layer part 4 of a magnetic layer 2 and the surface layer part 7 are saturated in one direction 5 by the magnet 10 attened with the relative movement and only the surface layer part 7 is magnetized in the reverse direction 8 by the magnet 11. When the direction of residual magnetization is inverted together in this way, a closed magnetic path is formed, the magnetic flux appearing externally is less and the residual magnetic flux is effectively less and then the residual noise and distortion factor are decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a magnetic erasing method, and more particularly to an erasing method with less residual noise and distortion.

<Prior Art> One of the methods for erasing information recorded on a magnetic recording medium such as a magnetic tape or a magnetic disk is a direct current erasing method.

The DC erasing method is a method in which a permanent magnet or an electromagnet is used to apply an erasing DC magnetic field to a magnetic recording medium to bring it into a state of saturated residual magnetization in a certain direction. Therefore, it is also called the saturation elimination method.

<Problems to be Solved by the Invention> The DC erasing method is simpler than other erasing methods (although it is easier to use than other erasing methods), since it creates a state of saturated remanent magnetization, it is difficult to eliminate large irregularities due to the minute irregularities on the surface of the magnetic recording medium. This method has the disadvantage of generating residual noise.It also has the disadvantage of a large distortion rate.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, it is an object of the present invention to provide a novel magnetic erasing method with less residual noise and less distortion.

Means for Solving the Problems〉 The magnetic erasing method according to the present invention that achieves the above-mentioned objects has the following features:
It is characterized in that a magnetic field is applied to the magnetic recording medium so that the directions of residual magnetization along the recording surface are reversed in the surface layer and the deep layer immediately below the surface layer.

Effect> When an erasing magnetic field is applied to a magnetic recording medium, previously recorded information is erased, whether it is a direct current magnetic field or an alternating current magnetic field.

In the case of B, the residual magnetic flux left in the magnetic recording medium by the erasing magnetic field is such that the direction of residual magnetization along the recording surface in the surface layer is opposite to the direction of residual magnetization along the recording surface in the deep layer immediately below, so magnetic recording is not possible. Since the magnetization vector is closed in the medium to form a closed magnetic path, it is hardly visible to the outside. That is, the effective residual magnetic flux is extremely reduced. Therefore, residual noise and distortion are reduced.

Example of implementation The present invention will be described in detail with reference to FIGS. 1 to 6.

First, an embodiment using a DC magnetic field is shown in FIGS. 1 to 4. FIG. 1 is a schematic cross-sectional view of the magnetic recording medium 1, in which the deep layer 4 of the magnetic layer 2 near the base 3 is DC magnetized to a saturation level in one direction along the recording surface 6 shown by the arrow 5.
The surface layer portion 71 near the recording surface 6 is DC magnetized in the opposite direction shown by the arrow 8 to a saturation level. 9 indicates the depth direction of the medium 1. As shown in FIG. 1, the surface layer 7 and the deep layer 4
When the directions of residual magnetization along the recording surface 6 are reversed, a closed magnetic path is formed and the magnetic flux exposed to the outside is reduced. That is, the residual magnetic flux is effectively reduced. In order to effectively reduce the residual magnetic flux to zero, it is sufficient to balance the thickness of the portion 4 that is magnetized in one direction 5 with the thickness of the portion 7 that is magnetized in the opposite direction 8.

FIG. 2 is an explanatory diagram showing an example of a specific method, in which two permanent magnets 10, 111i! They are arranged at intervals toward the recording surface 6 and along the direction 12 of relative movement with the magnetic recording medium 1. In this case, the strength of the magnetic pole of the preceding permanent magnet 10 and the distance from the recording surface 6 are set so that the DC magnetic field from the permanent magnet 10 is strong enough to saturate the deep layer 4. The trailing permanent magnet 11 is the leading permanent magnet 10
The strength of the magnetic pole or the distance from the recording surface 6 is such that the direct current magnetic field from the permanent magnet 11 reaches the deep layer 4 (although it does not reverse the magnetization in the surface layer 7). As a result, as the relative movement occurs, the entire magnetic layer 2, that is, the deep layer 4 and the surface layer 7, is first saturated magnetized in one direction 5 by the leading permanent magnet 10, and then the trailing permanent magnet 10 is magnetized to saturation in one direction 5. Only the surface layer 7 is magnetized in the opposite direction 8 by the permanent magnet 11.

The example shown in FIG. 3 differs from FIG. 2 only in that the preceding permanent magnet 10 is placed on the base 3 side. However, in the example shown in FIG. 3, it is not necessarily necessary to saturate magnetize up to the surface layer 7 using the preceding permanent magnet 10.

In both cases of FIG. 2 and FIG. 3, a magnetic head for recording, reproducing, re-recording, or erasing can be used instead of the permanent magnet 10.

In addition, when using a magnetic head, one
Only one magnetic head 13 is sufficient. 14 in Figure 4
15 is a DC power supply, 15 is an attenuator, and 16 is a switch for changing polarity and current value. At the beginning, as shown in Figure 4 (,),
A current is applied directly to the magnetic head 13 from the DC power supply 14 without passing through the attenuator 15, and the deep layer 4 is saturated in one direction 5. Next, by operating the switch 16 as shown in the same figure (bl), a current with reversed polarity is passed from the DC power supply 14 through the attenuator 15 to the magnetic head 13. The magnetization is reversed.As a result, the surface layer 7
The residual magnetization directions 8 and 5 are mutually reversed in the deep layer 4 and the deep layer 4.

Next, an embodiment using an alternating magnetic field will be described with reference to FIGS. 5 and 6.

Normally, the input/output characteristics in the short wavelength region of so-called longitudinal recording, in which a magnetic recording medium is magnetized along the recording surface, are as shown in Figure 5, and the recording current value at the MOL point is the point at which the recording current becomes higher. So, the reproduction output E of the magnetic head. IJT becomes minimal. MOL is the maximum playback output level (Max i
mumOutput Level). The reason for this is, as is well known, that when the recording wavelength is short, when the recording current is strengthened to magnetize the deep layer of the magnetic layer, the gap part of the magnetic head becomes magnetically saturated, which is called recording. This is said to be due to the generation of a rotating magnetization mode in which a portion of the residual magnetization vector is closed within the magnetic layer due to demagnetization and self-demagnetization effects. The rotational magnetization mode occurs more noticeably as the ratio λ/δ between the recording wavelength λ and the recording magnetization depth δ becomes smaller, the reproduction output decreases, and the recording current value at which the minimum reproduction output point occurs also becomes lower.

Therefore, as shown in FIG. 6, when applying a high frequency current to the magnetic head 13 to apply an alternating magnetic field to the magnetic recording medium 1, the speed v1 of the relative movement direction 12 between the magnetic recording medium 1 and the magnetic head 13 is By appropriately selecting the thickness δ of 2, the frequency f of the high-frequency current, and the current value I to record near the MIN point, the remanent magnetization direction 8 of the surface layer 7 and the remanent magnetization direction 5 of the deep layer 4 immediately below it can be determined. Invert. In the figure, 17 is an equiphase surface. 18 is a single frequency high frequency power source.

<Effects of the Invention> According to the present invention, since the residual magnetization vector closes at the same time as erasing, residual noise and distortion rate are small.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of a medium for explaining the principle of the method of the present invention when using a DC magnetic field, Figures 2, 3, and 4.
Figures (a) and (b) are explanatory diagrams of a specific example of the method. 5 and 6 relate to the method of the present invention using an alternating magnetic field, and FIG. 5 is a general input/output characteristic diagram for magnetic recording and reproduction;
FIG. 6 is a diagram explaining the principle. In the drawings, 1 is a magnetic recording medium, 2 is a magnetic layer, 3 is a base,
4 is the deep layer, 5 is the residual magnetization direction there, 6 is the recording surface, 7
8 is the direction of residual magnetization in the surface layer, 9 is the depth direction of the medium, 10 and 11 are permanent magnets or magnetic heads, 12 is the relative movement direction, 13 is the magnetic head, 14 is a DC power supply, 15
16 is an attenuator, 16 is a switch, 17 is an equal phase plane, and 18 is a high frequency power source.

Claims (1)

[Claims] A magnetic erasing method in which a magnetic field is applied to a magnetic recording medium so that the direction of residual magnetization along the recording surface is reversed between the surface layer and the deep layer immediately below the surface layer.