JPH0760535B2 - Magneto-optical reproducing magnetic head - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magneto-optical reproducing magnetic head suitable for reproducing a high definition video signal or the like.

[Conventional technology]

The main problems of magnetic recording in recent years are increasing the recording density to increase the capacity of the recording medium and increasing the frequency to enable high-speed access (that is, to increase the recordable band). For example, recently, a high-definition color television system has received much attention, but the video signal of this system has a wider frequency band than the video signal of the conventional system. In the case of high-density recording of such a wideband video signal, usually, the traveling speed of the magnetic medium is reduced to narrow the width of the track and eliminate the track pitch, thereby achieving high-density recording. When a conventional wire wound type magnetic head is used as the head, this is because the change in the magnetic flux due to the magnetization of the magnetic recording medium is directly converted into an electric signal by the winding, and the narrow width of the track causes the magnetic head to move. The playback output of will be reduced, and the C / N (carrier / noise) will be affected by the noise generated in the playback amplifier. In particular, when recording and reproducing a high-definition video signal, the deterioration of C / N becomes noticeable in the image quality. Therefore, it is conceivable to increase the number of windings in order to increase the reproduction output of the magnetic head. However, according to this, the inductance of the magnetic head increases and the transmission band becomes narrow, which also deteriorates the quality of the reproduced image. And cannot cope with higher frequencies.

Therefore, in order to solve such a problem, a method has been proposed in which information recorded at a high density is reproduced by utilizing the magneto-optical effect (Study of Technical Report Vol.1 No.42 1979.5 pp.
21-28 Tatsuo Nomura et al., "A study of magneto-optical recording method"). In this method, the magnetic flux change due to the magnetization of the magnetic recording medium is not directly converted into an electrical signal by the winding, but the magnetization pattern on the magnetic recording medium is transferred to the optical area effect film and scanned with a laser beam. The magneto-optical effect modulates the laser beam according to the intensity of the transferred magnetic pattern, and the modulated light beam is detected to reproduce the recorded information.

[Problems to be solved by the invention]

However, according to such a conventional method, a signal component having a recording wavelength shorter than the spot diameter of the laser beam cannot be reproduced, and the frequency band is limited in reproducing a wideband video signal. Further, in order to improve the S / N when the track width is narrowed and high density recording is performed, the strength of the magnetic pattern transferred to the magneto-optical effect film must be high. The thickness of the magnetic effect film may be increased to sufficiently transfer the magnetic pattern from the magnetic recording medium. However, in this case, the transferability of the magnetic pattern to the magneto-optical effect film is deteriorated.

As described above, in the past, there has been a problem that it is impossible to expect higher frequencies and improved S / N when high density recording is attempted.

The object of the present invention is to eliminate such problems, to achieve higher frequencies and S / S.
It is to provide a magneto-optical reproducing magnetic head capable of realizing a high recording density accompanied by an improvement in N.

[Means for solving problems]

In order to achieve this object, the present invention provides a non-magnetic magnetic layer in which a Faraday effect occurs in a part of a closed magnetic path through which a magnetic flux from a magnetic recording medium passes, and a light polarized in the easy-axis direction of the non-metallic magnetic layer is used. A magneto-optical reproducing magnetic head in which a beam is incident on the non-metal magnetic layer and the light beam that has passed through the non-metal magnetic layer is received by a light-receiving element via an analyzer. Are substantially orthogonal to the direction of the magnetic flux from the magnetic recording medium in the non-metal magnetic layer, and the light beam incident on the non-metal magnetic layer is polarized substantially parallel to the easy magnetization axis of the non-metal magnetic layer. The magnetic layer is provided with means for applying a DC bias magnetic field in a direction different from the direction of easy magnetization.

[Action]

The magnetization direction of the first non-metal magnetic layer that causes the Faraday effect largely rotates around the magnetization direction by the bias magnetic field according to the amount of magnetic flux from the magnetic recording medium, and the polarization plane of the incident light beam is thereby generated. Is rotated, and this light beam is received by a light receiving element through an analyzer whose polarization axis direction is fixed, whereby an information signal recorded on the magnetic recording medium is obtained from the light receiving element.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of a magneto-optical reproducing magnetic head according to the present invention, and FIG. 2 is a sectional view taken along the section line AA 'in FIG. Lower core, 3 upper core, 4 magnetic gap, 5 non-magnetic filling layer, 6 bias applying means, 7 non-metal magnetic layer, 8 laser beam,
Reference numeral 9 is a half mirror, 10 is a semiconductor laser, 11 is an analyzer, 12 is a light receiving element, and 13 is a light reflecting film.

This embodiment consists of a magnetic chip member and an optical system,
First, the structure of the magnetic chip member will be described.

1 and 2, a groove having a predetermined width is provided in a part of the substrate 1, and the lower core 2 is provided in the groove. A non-magnetic filling layer 5 is provided on the lower core 2,
The upper core 3 is provided thereon. The non-magnetic filling layer 5 is set thick enough to fill and separate the lower core 2 and the upper core 3, but is made sufficiently thin on the sliding surface side of the magnetic recording medium to form the magnetic gear 4. The lower core 2 and the upper core 3 are in contact with each other on the side opposite to the sliding surface with respect to the non-magnetic filling layer 5. Thereby, a closed magnetic circuit is formed by the lower core 2 and the upper core 3.

Here, further, a part of this closed magnetic circuit, in the figure, the upper core 3
A part of the non-magnetic filling layer 5 is composed of a non-metal magnetic layer 7 which produces the Faraday effect, and a light reflection film 13 is provided between the non-metal magnetic layer 7 and the non-magnetic filling layer 5. There is.
Further, bias applying means 6 is provided so as to penetrate the nonmagnetic filling layer 5 and face the nonmetal magnetic layer 7.

The above is the description of the configuration of the magnetic chip member. Next, the optical system will be described.

This optical system comprises a laser source 10, a light receiving element 12, a half mirror 9 and an analyzer 11.

A polarized laser beam 8 is output from the laser source 10. This passes through the half mirror 9 and enters the non-metal magnetic layer 7. The laser beam 8 is applied to the non-metal magnetic layer 7
The light is then reflected by the light reflection film 13 and then again passes through the non-metal magnetic layer 7, then is reflected by the half mirror 9, passes through the analyzer 11, and is received by the light receiving element 12.

In such a structure, when a magnetic recording medium (not shown) moves along the sliding surface on the magnetic gear 4 side, a magnetic flux having a strength corresponding to the recorded information signal of the magnetic recording medium causes a magnetic flux to be generated in the lower core 2. , The upper core 3 having the non-metal magnetic layer 7
Flowing through a closed magnetic circuit. In the non-metal magnetic layer 7, as shown in FIG.
It is set in a direction perpendicular to the flow direction of the magnetic flux indicated by 4 ', and the magnetization direction rotates according to the magnetic flux. That is, when there is no magnetic flux, the magnetization direction in the non-metal magnetic layer 7 coincides with the easy axis of magnetization indicated by the arrow 16, but if the magnetic flux flows in the direction of the arrow 14, the magnetization in the non-metal magnetic layer 7 The direction rotates clockwise on the drawing, as shown by arrow 15,
When magnetic flux flows in the direction of arrow 14 ', on the contrary, arrow 15'
Rotate counterclockwise as indicated by.

In FIGS. 1 and 2, the laser beam 8 from the semiconductor laser 10 is incident on the non-metal magnetic layer 7. The laser beam 8 is polarized in a direction substantially parallel to the easy magnetization axis direction of the non-metal magnetic layer 7 (that is, the direction of arrow 16 in FIG. 3) and passes through the non-metal magnetic layer 7 to emit light. While being reflected by the reflective layer 13 and passing through the non-metal magnetic layer 7 again, the plane of polarization is rotated by the Faraday effect. The laser beam 8 emitted from the non-metallic magnetic layer 7 is reflected by the half mirror 9 and is incident on the analyzer 11. Of these, only the component in the polarization axis direction of the analyzer 11 passes through the analyzer and the light receiving element. Light is received at 12.

Here, when the magnitude of saturation magnetization in the non-metal magnetic layer 7, the magnetization component in the incident direction of the laser beam 8 are M _S and M _⊥ , the Faraday rotation constant is F, and the thickness of the non-metal magnetic layer 7 is t, respectively. , The angle θ _f between the planes of polarization of the incident laser beam and the emitted laser beam of the non-metal magnetic layer 7 is expressed as follows.

When the nonmetallic magnetic layer 7 is provided with uniaxial anisotropy, the strength of the anisotropic magnetic field is H _K , and the strength of the magnetic field due to the magnetic flux from the magnetic recording medium is H _S , The above equation (1) can be further expressed as follows.

Figure 4 shows the angle θ _f and the ratio (H _S , H _K ) in equation (2).
And the operating characteristics of this embodiment.

In the figure, when the operation is performed such that the magnetization direction of the nonmetallic magnetic layer 7 is the easy axis of magnetization when the amount of magnetic flux from the magnetic recording medium is zero, the operating point is point P, The angle θ _f changes like a curve 18 according to the signal magnetic field 17 due to the magnetic flux from the magnetic recording medium. Angle θ _{f in} this case
Is small and changes at twice the frequency of the signal magnetic field 17. On the other hand, when operating at the operating point Q which is deviated from the operating point P, the change in the angle θ _f is large as shown by the curve 19, and the frequency of the change coincides with the frequency of the signal magnetic field 17.

In this embodiment, the operating point is thus shifted from the point P, and for this reason, the magnetization direction of the non-metal magnetic layer 7 when the signal magnetic field is zero is inclined from the easy magnetization axis direction. . As means for inclining the magnetization direction in this way, in FIG. 1 and FIG.
Is provided. When a DC bias current is passed through the bias applying means 6, a DC bias magnetic field is generated in the non-metal magnetic layer 7 in a direction orthogonal to the easy magnetization axis direction, whereby the magnetization direction is not the easy magnetization axis direction. Biased in different directions. Then, the desired operating point Q is set by appropriately setting the magnitude of the bias current.

The bias applying means 6 may be a permanent magnet.

FIG. 5 is a diagram for explaining the operation of the analyzer 13.

In the figure, when the polarization axis (polarized light transmission direction) of the analyzer 11 is the A-axis direction, the direction of the polarization plane of the laser beam 8 from the semiconductor laser 10 is in the B-axis direction which is deviated by 45 ° from the A direction. Set. Let this vector in the B direction be the laser beam 8 from the semiconductor laser 10. Now, when the non-metal magnetic layer 7 is magnetized so that magnetic flux passes in the direction of arrow 14 in FIG. 3, the laser beam 8 emitted from the non-metal magnetic layer 7 is + θ from the axis as shown by the vector.
_{Assuming that the} plane of polarization is rotated by _f , the analyzer 11 can pass only the component of the laser beam 8 in the A-axis direction, and the light receiving element 12 receives the laser beam represented by a vector. . Light intensity of this laser beam | A
| Is || = || cos (45 ° + θ _f ) = || cos (45 ° + θ _f ). When the non-metal magnetic layer 7 is magnetized so that a magnetic flux passes in the direction of the arrow 14 'in FIG. 3, the laser beam 8 emitted from the non-metal magnetic layer 7 is − The plane of polarization is rotated by θ _f .
Therefore, the laser beam received by the light receiving element 12 through the analyzer 11 in this case is represented by a vector ', and the amount of received light' is | '| = |' | cos (45 ° + θ _f ) = | | cos (45 ° + θ _f ).

As described above, the amount of light received by the light receiving element 12 varies depending on the rotation angle θ _f of the polarization plane of the laser beam 8 associated with the Faraday effect of the non-metal magnetic layer 7, and the rotation angle θ
_As shown in the above equation (2), _f varies depending on the strength H _S of the signal magnetic field due to the magnetic flux from the magnetic recording medium, so that the information signal recorded on the magnetic recording medium is electrically transmitted from the light receiving element 12. It will be obtained as a signal.

According to this embodiment, the shortest reproducible recording wavelength on the magnetic recording medium does not depend on the spot diameter of the laser beam 8 but on the magnetic gear, and the magnetic gear 4 can be formed sufficiently narrow. Higher frequency is greatly improved. In addition, the laser beam 8
Since the plane of polarization can be rotated, the reproduction level can be increased and C / N can be significantly improved.

Next, the material of each part of the magnetic chip member in FIGS. 1 and 2 will be specifically described.

Example 1: Crystallized glass was used as the substrate 1. The lower core 2 and the upper core 3 were formed by DC facing sputtering using Sendust as a material. The magnetic gap 4 and the non-magnetic filling layer 5 are made of Al ₂ O ₃ and are formed by a usual RF sputtering method. The non-metal magnetic layer 7 was made of (Gd ₂ Bi) Fe ₅ O ₁₂ as a material and was formed by a normal RF sputtering method. Bias applying means 6 when the light reflecting film 13 and the coil are used
Was formed by a vacuum deposition method using Cu as a material. Then, patterning was performed on these members by using a normal photolithographic technique mainly based on the ion milling method.

The magnetic chip member formed as described above includes a lower core 2, an upper core 3 and (Gd ₂ Bi) Fe ₅ O made of sendust.
_In order to ensure the predetermined characteristics of the non-metal magnetic layer 7 by ₁₂ , the wafer is heat-treated at 500 to 700 ° C. for 1 hour, and then processed into a desired shape, as shown in FIGS. The configuration is shown in.

According to this, an improvement of about 3 dB in C / N was recognized as compared with the conventional wound magnetic head.

Example 2: As the material of the non-metallic magnetic layer _{7 (Gd 3-x Bi x} ) Fe 5 O 12 ( where, 1 <x ≦ 2) using the same procedure as in Example 1 row Natsuta. Even in this case, the same effect as in Example 1 was obtained.

〔The invention's effect〕

As described above, according to the present invention, when the rotation of the plane of polarization of the light beam due to the signal magnetic field is detected to reproduce the signal, the bias magnetic field is applied to the non-metal magnetic layer in a direction different from the easy magnetization axis direction. Since it is applied, the rotation of the magnetization direction in the non-metal magnetic layer due to the amount of magnetic flux from the recording medium becomes large, the reproduction level can be increased and the C / N is greatly improved. Since the shortest recording wavelength is determined by the magnetic gear, the reproducible upper limit frequency can be increased, and high density recording and high frequency recording of the recording medium can be further improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a magneto-optical reproducing magnetic head according to the present invention, FIG. 2 is a sectional view taken along the section line AA 'in FIG. 1, and FIG. FIG. 4 is a schematic diagram showing the change of the magnetization direction in the metal magnetic layer, FIG. 4 is an operation characteristic diagram of this embodiment, and FIG. 5 is an explanatory diagram of the action of the analyzer in FIG. 1 ... Substrate, 2 ... Lower core, 3 ... Upper core, 4 ...
Magnetic gear, 5 ... Non-magnetic filling layer, 6 ... Bias applying means, 7 ... Non-metal magnetic layer, 8 ... Light beam, 9 ...
Half mirror, 10 ... Semiconductor laser, 11 ... Analyzer, 12
…… Light receiving element, 13 …… Light reflecting film.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masakatsu Saito Masakatsu Saito, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa, Ltd. Home Appliances Research Laboratory, Hitachi, Ltd. (72) Katsuyuki Tanaka, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Ceremony Company Home Appliance Research Laboratory, Hitachi, Ltd.

Claims (1)

[Claims] 1. A Faraday effect is generated in a part of a closed magnetic path which has a magnetic gap on the sliding surface side of a magnetic recording medium and through which a magnetic flux corresponding to the intensity of magnetization due to information signal recording of the magnetic recording medium passes. The information signal is electrically converted by forming a metal magnetic layer and by injecting a polarized light beam into the non-metal magnetic layer and receiving the light beam whose polarization plane is rotated by the non-metal magnetic layer through an analyzer. In the magneto-optical reproducing magnetic head that is obtained as a signal, the easy axis of magnetization of the non-metal magnetic layer substantially coincides with the thickness direction of the non-metal magnetic layer, and the light beam incident on the non-metal magnetic layer Is polarized substantially parallel to the easy magnetization axis direction of the non-metal magnetic layer, the non-metal magnetic layer is orthogonal to the easy magnetization axis direction, and the magnetic flux propagation direction in the closed magnetic path other than the non-metal magnetic layer. Almost parallel to A means for applying a direct current bias magnetic field is provided, and the magnetization direction in the non-metal magnetic layer is rotated around the magnetization direction by the bias magnetic field in accordance with the magnetic flux from the magnetic recording medium. A magneto-optical reproducing magnetic head characterized in that the electric signal having a large amplitude and a frequency equal to that of an information signal can be obtained.