JPS6023401B2 - Magnetic recording and reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel magnetic recording and reproducing method, and more particularly to a novel magnetic recording and reproducing method that uses a magnetic layer consisting of two layers and is capable of recording and reproducing short wavelength signals as well. It is something.

Magnetic recording, in which information is recorded and reproduced by moving an electromagnetic conversion element such as a magnetic head close to the surface of a magnetic recording medium such as a magnetic tape, can be used to record or reproduce information such as audio signals, video signals, measurement signals, or digital signals for computers. It is widely used for recording and reproducing.

In recent years, there has been a demand for a method of recording shorter wavelength signals on a magnetic recording medium in order to further increase the recording density.
However, in conventional magnetic recording systems, it is difficult to record signals with very short wavelengths due to the recording demagnetization effect.
That is, when the magnetic recording body moves in opposition to the recording head, the recording point in the recording body receives polarity reversal of the signal magnetic field from the recording head, so that a rotational magnetization mode occurs in the magnetic recording body. Since this rotating magnetization mode has a closed magnetic path structure, the leakage magnetic flux to the outside of the magnetic recording medium is significantly reduced, and since there are no lines of magnetic force to be picked up by the reproducing head, it appears as if no recording had been made, and no reproducing output is obtained. I can't do it. This phenomenon was more pronounced when the recording wavelength was short.If the recording current was increased, the reproduction output increased to some extent, but this soon reached its maximum value, and when the recording current was further increased, the reproduction output suddenly decreased. After that, it clearly appears as a dip phenomenon in which it takes a second maximum value again. This phenomenon is observed in both bias magnetic recording and non-bias magnetic recording, and has been a major obstacle in increasing the density of magnetic recording. However, by converting the closed magnetic path structure of the above-mentioned rotating magnetization mode into an open magnetic path that generates leakage magnetic flux outside the recording medium, it is possible to record and reproduce short wavelengths with large amplitudes that were conventionally considered impossible to record and reproduce. This is disclosed in the official gazette of Tokukan Sho 51-17421. In this method, after normal magnetic recording is performed on a magnetic recording medium using a bias method or a non-bias method using a recording head, the rotational magnetization mode is destroyed by applying a DC magnetic field substantially in the thickness direction of the magnetic recording medium. This generates a perpendicular magnetization component, which is then read out by a reproducing head. It is said that the magnitude of the DC magnetic field is 2 to 5 times the coercive force of the magnetic recording medium, and that the direction of application of the magnetic field is preferably slightly inclined from the axis perpendicular to the surface of the magnetic recording medium. However, in this method, a large magnetic field of 500 to 2000 degrees must be used as a DC magnetic field, and it is not practical to attach such a high DC magnetic field applying device to a magnetic recording/reproducing apparatus. Furthermore, in this method, the rotating magnetization mode is completely destroyed by the applied DC magnetic field, so it is necessary to readjust it by applying a DC magnetic field or to re-save the signal as the rotating magnetization mode. The problem is that it is not suitable for practical use. In view of these circumstances, the present invention is capable of converting a closed magnetic path structure in a rotating magnetization mode into an open magnetic path structure without using a large direct current magnetic field, and therefore can achieve sufficient reproduction output with a practical device. It is capable of short wavelength recording and does not completely destroy the rotating magnetization mode.
The object is to provide a magnetic recording and reproducing method.

The method of the present invention comprises: a first magnetic layer having a lower coercive force at low temperatures than at room temperature; A signal is recorded by applying a signal magnetic field of a magnitude that can magnetize only the second magnetic layer at room temperature to a magnetic recording medium having a two-layered magnetic layer consisting of a second magnetic layer that increases in temperature at low temperatures. Next, this recording body is cooled and a DC magnetic field of a magnitude that can magnetize only the first magnetic layer is applied in the thickness direction of the magnetic recording body at a low temperature, and then the signal is reproduced at room temperature. It is characterized by: That is, according to the method of the present invention, a signal is first recorded only in the second magnetic layer at room temperature by utilizing the difference in coercive force between the two magnetic layers. As mentioned above, since the magnetization pattern becomes a loop-shaped closed magnetic path, a sufficient reproduction output cannot be obtained.
Next, when the recording medium is cooled so that the first magnetic layer has a higher coercive force than the second magnetic layer, and a DC magnetic field is applied,
Only the first magnetic layer is DC magnetized. Next, when the recording medium in which the first magnetic layer has direct current magnetization and the second magnetic layer has a magnetization component with a closed magnetic path structure is returned to room temperature, the coercive force of the second magnetic layer becomes the same as that of the first magnetic layer. Since the coercive force of the magnetic layer is lower than that of the magnetic layer, the closed magnetic circuit structure of the second magnetic layer is influenced by the DC magnetization of the first magnetic layer, and the magnetization in the same direction as this DC magnetization is strengthened, and the magnetization in the opposite direction is Since the magnetization is weakened, it is converted into an open magnetic path structure. Therefore, external leakage magnetic flux is generated, and sufficient reproduction output can be obtained. As described above, according to the method of the present invention, even short wavelength signals can be recorded with sufficient final reproduction output. Furthermore, unlike the method described in JP-A-51-17421, it is possible to use a material whose coercive force at low temperatures is extremely small, such as a magnetic powder mainly composed of Nh-Bi alloy, as the first magnetic layer. The magnetization pattern can be formed into an open magnetic path structure by applying a DC magnetic field of relatively 4 cm.

Furthermore, the open magnetic path structure of the second magnetic layer becomes an open magnetic path structure under the influence of the DC magnetization of the first magnetic layer.
By removing the DC magnetization of the first magnetic layer, the closed magnetic circuit structure can be returned to the almost original state.

In order to remove this DC magnetization, the magnetic recording body is cooled again, and the coercive force of the first magnetic layer is made lower than the coercive force of the second magnetic layer, so that the second magnetic layer is not affected. It is sufficient to demagnetize only the first magnetic layer by applying an attenuated alternating current magnetic field of the same magnitude. Note that in order to record a signal on the second magnetic layer, either a bias method or a non-bias method may be used. Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing an example of a magnetic recording body used in the present invention.

The recording body 1 of this example has a first magnetic layer 1 on a nonmagnetic substrate 10.
1 and a second magnetic layer 12 are stacked in this order.

The first magnetic layer 11 has a coercive force lower than that at room temperature at low temperatures, and the second magnetic layer 12 has a coercive force lower than that of the first magnetic layer 11 at room temperature, but becomes higher at low temperatures. The magnetic material for the first magnetic layer 11 is desirably composed mainly of Nm-Bi alloy.

As shown by curve A in Figure 2, the Mn-Bi alloy has a high coercive force of several hundred e or more at room temperature, but the coercive force decreases markedly at low temperatures, especially around -200o0.
It decreases to about e. Other magnetic materials used for the first magnetic layer 11 include magnetic materials that have a large magnetic anisotropy constant near room temperature, such as M old i, and whose magnetic anisotropy constant decreases when cooled to below room temperature. Or, like barium ferrite, the K/ls value (K: magnetic anisotropy constant, ls: saturation magnetization) decreases as the temperature decreases,
A magnetic material is used in which a single magnetic domain structure at room temperature becomes a multi-domain horizontal structure at low temperatures, resulting in a low coercive force. Although the magnetic material constituting the second magnetic layer 12 has a relationship with the magnetic material of the first magnetic layer 11, it has a lower coercive force than the first magnetic layer at room temperature, and increases in coercive force when cooled to a low temperature. However, it is sufficient to use a magnetic material that does not change, or a magnetic material that has a coercive force higher than that of the first magnetic layer 11 even if its coercive force decreases, and the range of selection is wide. This includes iron oxide magnetic powder, Co-containing iron oxide magnetic powder, Cr
Particularly preferred are 02 magnetic powder, alloy magnetic powder, and the like. For comparison, temperature changes in coercive force of alloy powder (70% Fe, 30% Co) and Co-containing iron oxide powder are shown in FIG. 2 as curves B and C, respectively. In the method of the present invention, a magnetic recording head 20 is moved as shown in FIG. 3A over a recording medium 1 as shown in FIG. 1, and a short wavelength signal magnetic field is applied to this recording medium 1. .

The magnitude of this signal magnetic field is selected so that a signal is recorded only in the second magnetic layer 12, taking into consideration the difference in coercive force between the first and second magnetic layers 11 and 12 at room temperature. layer 1
When a Mh-Bi alloy is used for the second magnetic layer 12 and a magnetic material as described above is used for the second magnetic layer 12, the Mh-Bi alloy is used at room temperature.
Since the coercive force of the i-alloy is extremely large compared to those materials, the magnitude of the signal magnetic field may be the magnitude commonly used. At this time, since the signal has a short wavelength, a loop-shaped closed magnetic path 31 is formed in the second magnetic layer 12 as described above.

Next, the recording body 1 thus constructed is cooled and a DC magnetic field is applied in the thickness direction of the recording body 1, that is, in a direction intersecting the first and second magnetic layers 11 and 12. The magnitude of this DC magnetic field is selected so as to magnetize only the first magnetic layer 11 in consideration of the coercive force of both magnetic layers at low temperatures.
In the case of alloys, the coercive force is extremely low at low temperatures, so a relatively small magnetic field is sufficient. As a result, the first magnetic layer 11 is magnetized and a DC magnetic field 32 is generated, as shown in FIG. 3B. The direction in which the DC magnetic field is applied should be somewhat aligned with the axis 13 perpendicular to the surface of the magnetic recording medium 1, as shown by the arrow 21, and the magnitude of this disturbance can be easily determined experimentally. be able to. In this way, when the recording medium 1 in which the first magnetic layer 11 has the DC magnetization 32 and the second magnetic layer 12 has the loop-shaped closed magnetic path 31 is returned to room temperature, the coercive force of the second magnetic layer 12 changes to the first Since it is lower than the magnetic layer 11, the closed magnetic path 31 of the second magnetic layer 12 is influenced by the DC magnetization 32 of the first magnetic layer 11 and is converted into an open magnetic path structure (see FIG. 3C). That is, among the loop-shaped closed magnetic paths 31, those in the same direction as the DC magnetization 32 are strengthened, and those in the opposite direction are weakened, resulting in unidirectional magnetization 33. The external leakage magnetic flux due to this unidirectional magnetization 33 can be sufficiently picked up by the reproducing head 22. Therefore, according to the method of the present invention, even short wavelength signals can be recorded and reproduced with sufficient reproduction output. Furthermore, since the above-mentioned unidirectional magnetization 33 is obtained by the magnetic field caused by the DC magnetization 32 of the first magnetic layer 11, if the DC magnetization 32 is removed, the DC magnetic field applied to the second magnetic layer 12 will disappear. The magnetization pattern of the second magnetic layer 12 returns to the original loop-shaped magnetization pattern to some extent.

This tendency is particularly strong if the second magnetic layer 12 does not have very large magnetic anisotropy in the perpendicular direction. In order to remove the DC magnetization 32 of the first magnetic layer 11, if the magnetic recording body 1 is cooled to a low temperature and an attenuated AC magnetic field is applied, the coercive force of the second magnetic layer 12 will be higher than that of the first magnetic layer 11. Only the DC magnetization 32 of the first magnetic layer 11 can be erased. First magnetic layer 11
It is advantageous in carrying out the method of the present invention if it is formed to have an easy axis in the direction 21 of the DC magnetic field. In addition,
As a matter of course, the first magnetic layer 11 and the second magnetic layer 12
are laminated in this order on the substrate 10 in the illustrated embodiment, but they may be laminated in the reverse order.

This is because, in practice, it is well known that the depth of the magnetic layer for recording signals can be varied in any way by changing the depth of the magnetic flux of the head. As described above in detail, according to the method of the present invention, even short wavelength signals can be recorded and reproduced with sufficient reproduction output, and therefore signals can be recorded with high density.

Furthermore, it is advantageous in terms of equipment since there is no need to apply a large DC magnetic field. Furthermore, since the rotating magnetization mode is not completely destroyed, it is possible to re-save the signal as the rotating magnetization mode during readjustment by applying a DC magnetic field.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of a magnetic recording medium used in the method of the present invention, FIG. 2 is a graph showing changes in coercive force of magnetic materials with temperature, and FIGS. 3A to 3C are each of the methods of the present invention. It is a figure for showing the state of magnetization in a stage. DESCRIPTION OF SYMBOLS 11...First magnetic layer, 12...Second magnetic layer, 31.
・...Loop-shaped closed magnetic path, 32...DC magnetization, 33.
...unidirectional magnetization. Figure 1 Figure 2 Figure 3A Figure 38 Figure 3C

Claims (1)

[Claims] 1. A first magnetic layer having a coercive force lower at low temperatures than at room temperature, and a second magnetic layer laminated thereon, whose coercive force is lower at room temperature and higher at low temperatures than the first magnetic layer. By applying a signal magnetic field at room temperature to a magnetic recording body having a magnetic layer consisting of a magnetic layer, only the second magnetic layer is magnetized and a signal is recorded. A magnetic recording and reproducing method, characterized in that only the first magnetic layer is magnetized by applying a DC magnetic field in the horizontal direction, and then the signal is reproduced at room temperature. 2. The magnetic recording and reproducing method according to claim 1, wherein the first magnetic layer contains magnetic powder mainly composed of Mn-Bi alloy. 3. The magnetic recording and reproducing method according to claim 2, wherein the DC magnetic field is applied at a low temperature of approximately -200°C. 4. Claim 1 or 4, wherein the second magnetic layer contains at least one kind of magnetic powder selected from iron oxide magnetic powder, Co-containing iron oxide powder, CrO_2 magnetic powder, and alloy magnetic powder. The method described in Section 2.