JPS5927964B2 - How to demagnetize magnetic materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for demagnetizing a magnetic material having magnetic anisotropy, such as a magnetic tape.

FIGS. 1 and 2 show a conventional degaussing method of this type.

The degaussing method shown in FIG.
With respect to the magnetic film formed on the surface of
The magnetic field ψ1 of . The configuration is such that the voltage is applied. The degaussing method shown in FIG. 2 has a configuration in which a degaussing head 2 applies a magnetic field ψ2 in a direction b perpendicular to the easy magnetization axis direction a to the magnetic film of the magnetic tape 1. FIG. 3 shows an erasing characteristic curve diagram of the conventional degaussing method shown in FIGS. 1 and 2.

In the figure, the horizontal axis represents the applied magnetic field H (Oe), and the vertical axis represents the erasure rate η (dB). Curves Al and A2 show the erasing characteristic curves in the degaussing method shown in Fig. 1, and the curve Al is the magnetic field ψ.
, is a DC magnetic field, and curve A2 shows the respective erasing characteristic curves when the magnetic field ψ1 is an AC magnetic field.
Curves B1 and B2 show the erasing characteristic curves in the degaussing method shown in Figure 2, curve B7 shows the erasing characteristic curves when the magnetic field ψ2 is a DC magnetic field, and curve B2 shows the erasing characteristic curves when the magnetic field ψ2 is an AC magnetic field. show.

As shown in FIG. 3, the conventional degaussing method shown in FIG. 1 has a much better erasing rate than the demagnetizing method shown in FIG. Among the demagnetizing methods shown in Fig. 1, the DC demagnetizing method is such that a DC magnetization component remains in the magnetic film on the magnetic tape 1 after the degaussing operation, and the part of the magnetic tape 1 where the magnetic film is formed is integrally attached to the magnetic film. A rapid change in magnetization occurs at the boundary with the leader tape connected to the magnetic field, and at the boundary between the two when DC erasing is performed and then AC erasing is performed.

Reproducing heads such as tape recorders generally extract temporal changes in magnetization in a magnetic film as magnitudes of electromotive force, so if there is a sudden change in magnetization as described above,
It makes a lot of noise and is very harsh on the ears. Furthermore, if a recording signal is placed in an area where DC magnetization remains, there is also the disadvantage that the distortion rate worsens. Also, among the degaussing methods shown in Figure 1, the AC degaussing method is currently used in ordinary tape recorders, and has very good characteristics during normal use with ordinary magnetic tapes. In the case of high coercive force tape such as metal magnetic tape, or when demagnetizing without contacting the magnetic tape, a fairly large alternating current is required, so the head itself has to be considerably large, including thermal design. It has the disadvantage of getting used to it. Furthermore, if it is desired to increase the relative speed between the magnetic tape and the magnetic head, the frequency of the alternating current must be increased accordingly, which leads to further increase in the size of the magnetic head, resulting in a considerably large-scale device. There is a drawback that it becomes impractical. On the other hand, with the demagnetization method shown in Figure 2, no DC magnetization remains whether the magnetic field is an AC magnetic field or a DC magnetic field, but as shown in Figure 3, the erasure rate is very poor and it is not practical. In order to obtain a satisfactory erasure rate,
For example, it is necessary to apply a large magnetic field of about 10K (0e), which is not practical.

The present invention eliminates the drawbacks of the conventional degaussing method described above, and demagnetizes without leaving any DC magnetization by simply applying a relatively small magnetic field, which causes noise generation and deterioration of distortion rate in recording. The purpose is to provide a degaussing method that does not require degaussing.

In order to achieve the above object, the present invention provides a method for demagnetizing a magnetic material having magnetic anisotropy, in which a DC magnetic field is applied to the magnetic material in the direction of the axis of easy magnetization, and then a direct current magnetic field is applied to the surface of the magnetic material. It is characterized in that a DC magnetic field is applied in parallel to the magnetic field and in a direction perpendicular to the axis of easy magnetization.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The content of the present invention will be explained in detail below with reference to the drawings which are examples.

FIG. 4 shows an explanatory diagram of the demagnetization method according to the present invention.
In the figure, 3 indicates a magnetic tape, and 4 and 5 indicate reels around which the magnetic tape 3 is wound. The magnetic tape 3 is wound and runs in the direction of arrow a between the reels 4 and 5 during the demagnetization operation. In addition, the axis of easy magnetization of the magnetic film of the magnetic tape 3 is
It generally corresponds to its longitudinal direction a or al. 6
is a DC demagnetizing head.

The DC demagnetizing head 6 is opposed to the magnetic film surface of the magnetic tape 3 with a gap G1 interposed therebetween. Also, the DC demagnetization head 6
The magnetic pole NS is disposed in the easy magnetization axis direction a or a'' of the magnetic tape 3, and is configured to apply a DC magnetic field ψ in the easy magnetization axis direction a or a' to the magnetic film of the magnetic tape 3. The DC demagnetization head 6 may be a permanent magnet or may be an electromagnetic type that is excited by passing a DC current.If it is configured with a permanent magnet, there will be no energy loss and the efficiency will be extremely high. When using the electromagnetic method, it is easy to design the impedance because it is a direct current, and there is no need for a complicated circuit to create an alternating current.Furthermore, heat generation is only caused by copper loss, so there is no iron loss in the yoke. There are advantages such as ease of thermal design.The degaussing head 7 is opposed to the magnetic film surface of the magnetic tape 3 with an air gap G2 in between, and its magnetic poles are placed on both sides of one side of the magnetic tape 3 in the width direction. A magnetic field ψ4 is applied in parallel to the magnetic film surface of the magnetic tape 3 and in a direction b perpendicular to the axis of easy magnetization a or a''.

With this configuration in which the demagnetizing magnetic field ψ4 is applied parallel to the magnetic film surface of the magnetic tape 3, the demagnetizing head 7 can be positioned on one side of the magnetic film surface of the magnetic tape in a normal magnetic tape cassette or the like. It is possible to apply a demagnetizing effect while maintaining the normal running configuration without adopting a structure such as pulling out the magnetic tape 3, and as will be explained later in FIG. 6, the shape of the magnetic tape winding body can be However, advantages such as demagnetization can be obtained. The magnetic field ψ4 caused by this demagnetizing head 7
is a direct current magnetic field.

When using a DC magnetic field, in addition to the fact that the demagnetizing head 6 is a DC demagnetizer, both the demagnetizing heads 6 and 7 can be constructed from permanent magnets or DC electromagnets, so overall energy loss is reduced. It is possible to realize a small and inexpensive degaussing device with easy impedance design and thermal design. Next, the demagnetizing effect of the present invention will be explained in detail with reference to FIGS. 4 and 5. FIG. 5a shows an erasing characteristic curve diagram, in which the horizontal axis represents the applied demagnetizing magnetic field H of the demagnetizing head 6, and the vertical axis represents the erasing rate η(DB). Curve A3 is degaussing head 6
shows the extinction curve. In the portion of FIG. 5b, the vertical axis represents the peak voltage Vp (v) of noise due to DC magnetization, and the horizontal axis represents the applied demagnetizing magnetic field H (0e) of the demagnetizing head 7. Curve C shows the peak voltage curve of noise due to degaussing head 7. In addition, the lower part has the same applied demagnetizing magnetic field H (0
e), and the erasure rate η(DB) is plotted on the vertical axis, and the curve A4 shows the erasure curve by the demagnetizing head 7. When the magnetic tape 3 is wound and run in the direction of the arrow a between the reels 4 and 5, a magnetic field ψ3 in the easy magnetization axis direction a is applied from the degaussing head 6 to the magnetic film surface of the magnetic tape 3, and the magnetic tape 3 is demagnetized as shown by curve A3.

If the strength of the magnetic field ψ3 is H1 (0e), then the erasure rate of the magnetic tape 3 is η1 (DB), and the DC magnetization corresponding to this erasure rate η1 (DB) is the magnetic film surface of the magnetic tape 3. remains in After being subjected to the demagnetizing action by the aforementioned demagnetizing head 6, the magnetic tape 3 is exposed to the magnetic field ψ4 of the demagnetizing head 7.
guided inside.

The magnetic field ψ4 of the degaussing head 7 is in a direction b perpendicular to the axis of easy magnetization a of the magnetic tape 3, and due to this magnetic field ψ4, the noise peak voltage due to the DC magnetization component remaining on the magnetic tape 3 is changed as shown by the curve C. It decays as follows. If the strength of the magnetic field ψ4 at which this noise peak voltage becomes O is approximately H2, then the erasing rate of the magnetic tape 3 by the degaussing head 7 is η2 (DB).
becomes. FIG. 6 shows another embodiment of the invention.

In the figure, 8 is a magnetic tape winding body, and 9 and 10 are degaussing heads. The demagnetizing head 9 corresponds to the DC demagnetizing head 6 shown in FIG. 4, and has a rod-shaped permanent magnet or the like having magnetic poles N and S formed at both ends thereof, which is arranged opposite to the magnetic tape roll 8 through a gap G3. It has been done. Since the axis of easy magnetization of the magnetic tape winding 8 is in the circumferential direction, by rotating the degaussing head 9 or the magnetic tape winding 8 relatively around the axis 01 as shown by the arrow d. , DC demagnetization can be applied to the magnetic tape wound body 8 in the direction of the axis of easy magnetization. Further, the direction perpendicular to the easy magnetization axis direction of the magnetic tape wound body 8 is the axial direction X.

Therefore, the axial direction of the magnetic tape winding body 8 is aligned with the direction of the magnetic poles Pl and P2 of the degaussing head 10, and the magnetic pole P1
, , P2, and by relatively moving the demagnetizing head 10 or the magnetic tape winding 8 in parallel, the DC magnetization component generated by the demagnetizing action of the demagnetizing head 9 can be removed. can be erased. As described above, the present invention provides a method for demagnetizing a magnetic material having magnetic anisotropy, in which a DC magnetic field is applied to the magnetic material in the direction of its easy magnetization axis, and then the surface of the magnetic material is further demagnetized. Since the DC magnetic field is applied in a direction parallel to the axis of magnetization and perpendicular to the axis of easy magnetization, the following effects can be obtained.

(1) By simply applying a relatively small magnetic field, it is possible to demagnetize without leaving any DC magnetization, thereby preventing the generation of noise and deterioration of the distortion rate during recording.

For example, in the case of a normal magnetic tape, a DC magnetic field of about 1K to 2K Gauss in the direction of the easy magnetization axis is applied, and 2K to 2K Gauss is applied.
A practically sufficient demagnetizing effect can be obtained simply by applying a magnetic field of about 3 K Gauss in a direction perpendicular to the axis of easy magnetization. (2) Since the demagnetizing magnetic field may be small as described above, it is possible to demagnetize in a non-contact state while suppressing the enlargement of the demagnetizing head. Therefore, although the device is small, it is possible to demagnetize the tape by running it at high speed while protecting the magnetic material such as the magnetic tape from abrasion and abrasion damage. Further, even for high coercive force tapes such as metal tapes, sufficient erasing characteristics can be ensured despite the small size.

(3) Since this method applies a DC magnetic field as a magnetic field in the direction of the easy axis of magnetization and a magnetic field in a direction perpendicular to the axis of easy magnetization, the degaussing head for generating this DC magnetic field is configured with a permanent magnet or a DC electromagnet. be able to.

Therefore, it is possible to provide an inexpensive demagnetizing device with less energy loss and easy impedance design and thermal design. (4) Easy magnetization Since the structure is such that a DC magnetic field in a direction perpendicular to the magnetization direction is applied parallel to the surface of the magnetic material, in a normal magnetic tape cassette, etc., the degaussing head is used to Position it on one side of the membrane surface,
It is possible to provide a demagnetizing effect while maintaining the normal running configuration without adopting a structure such as pulling out the magnetic tape.

Therefore, the degaussing operation becomes easy and a degaussing device with a simple structure can be realized. (5) Furthermore, since the structure is such that a direct current magnetic field in a direction perpendicular to the direction of easy magnetization is applied parallel to the surface of the magnetic material, as shown in FIG. can also be demagnetized, making the demagnetization process very easy.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams of the conventional degaussing method, FIG. 3 is an erasing characteristic curve diagram, FIG. 4 is an explanatory diagram of the demagnetizing method and device according to the present invention, and FIGS. 5A and 5B are the same. The erasure characteristic curve diagram and FIG. 6 similarly show explanatory diagrams of other embodiments. 3... Magnetic tape, 6, 7, 9, 10...
...Demagnetizing head, 8...Magnetic tape winding body, A
, a''... Easy magnetization axis direction, b...... Direction perpendicular to the easy magnetization axis direction.

Claims (1)

[Claims] 1. In a method of demagnetizing a magnetic material having magnetic anisotropy, after applying a DC magnetic field to the magnetic material in the direction of its axis of easy magnetization, further parallel to the plane of the magnetic material,
A demagnetization method characterized in that a DC magnetic field is applied in a direction perpendicular to the easy axis direction of magnetization.