JPH0793837A - Magnetic recording and reproducing method and reproducing head using same - Google Patents

Abstract

PURPOSE:To make a ratio of a signal to noise S/N large by making a rotation angle of a plane of polarization large. CONSTITUTION:In the magnetic recording and reproducing method utilizing magnetoelectric transducing for transducing a change in a magnetically recorded magnetic domain pattern (recording contents) via its optical change into an electric signal (regenerative signal), the direction of an optical axis and a direction of magnetic flux to be generated from the recorded magnetic domain are arranged to have an angle other than right angles to each other. Moreover, magnetoelectric transducing by the magnetic Faraday effect is utilized. Thus, a large S/N as compared with a reproducing head utilizing the magnetic Kerr effect is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing technique of a magnetic domain pattern recorded in high density magnetic recording, and relates to a reproducing head and a magnetic recording reproducing method for reproducing magnetic recording contents recorded in an extremely high density state. . INDUSTRIAL APPLICABILITY The magnetic recording / reproducing method and reproducing head according to the present invention can be used for reproducing ordinary magnetic recording, and further can be used as a reproducing head for magnetic recording constituting a high-density recording system such as a digital image recording / reproducing system. it can. In particular, the reproducing head according to the present invention can reproduce magnetic recording recorded at a high track density and can be used in a multi-track magnetic recording system.

[0002]

2. Description of the Related Art Recently, a technique for recording a large amount of information has been actively researched. Recently, a magneto-optical recording system has begun to be used as an information recording device for a computer system. As a system for recording image information, V
As an advanced type of TR system, high definition VTR,
Furthermore, digital VTRs are being studied.

The digital VTR system is researching and developing various systems for each electric manufacturer. As one of those systems, Thomson, France, has developed a high-quality digital VTR system using a multi-head type magnetic recording head, a reproducing head utilizing the magnetic Kerr effect, and a magnetic tape medium. FIG. 1 illustrates the concept of the VTR system manufactured by Thomson and the configuration and principle of each head used.

FIG. 1a shows the configuration of a digital VTR system using a magnetic tape magnetically recorded at a high track density using a magnetic recording head and a reproducing head. Recording is performed at an extremely high track density by a magnetic recording head formed by arranging a plurality of normal ring type heads in rows. Then, the magnetic recording is composed of a portion which irradiates the head core portion with light and performs magnetic-electric conversion by utilizing the magnetic Kerr effect.

FIG. 1b shows the structure of the magnetic recording head. The magnetic recording head is formed by arranging a plurality of normal ring type heads in parallel. The operating principle of the reproducing head is shown in FIG. 1c. The reproducing head is a unique head that obtains a reproducing signal by using a magneto-optical transducer utilizing the magnetic Kerr effect.

The magnetic Kerr effect is a phenomenon in which, when linearly polarized light is applied to a magnetic material, the polarization plane of the reflected light rotates with respect to the polarization plane of the incident light. The reproducing head used in this digital VTR system exhibits its function by utilizing this magnetic Kerr effect. It is used in a magneto-optical recording system for computers and a mini-disc digital audio system, which have recently been put on the market.

The operation principle of the reproducing head will be briefly described. Incident light generated by a laser diode and converted into linearly polarized light by a polarization optical system rotates a plane of polarization due to a magnetic Kerr effect by a magneto-optical transducer according to a magnetic recording content. Cause Since the direction of this rotation differs depending on the magnetization direction of the recording magnetization, when the reflected light that has passed through the analyzer optical system is detected by the optical sensor, it is detected as a change in light intensity according to the recording magnetization. That is, the magnetic recording content can be reproduced.

FIG. 2 shows the relationship between the direction of magnetic flux flowing in the magneto-optical transducer of the reproducing head, that is, the direction of magnetically recorded magnetization and the direction of rotation of the polarization plane caused by the magnetic Kerr effect. In FIG. 2, the states A and B correspond to the states in which the directions of the magnetic flux are antiparallel. As is apparent from FIG. 2, the rotating direction of the change surface due to the magnetic Kerr effect is reversed in accordance with the magnetically recorded contents. Therefore, the magnetic recording content can be known, that is, the magnetic recording content can be reproduced from the rotation direction of the polarization plane extracted as an electrical signal by the optical sensor.

As described above, the magnetic recording / reproducing head of the Thomson Digital VTR system is constructed by using the magnetic Kerr effect, and it is possible to reproduce the magnetic recording contents recorded in an extremely high density state. Is. Particularly, as shown in FIG. 1a, magnetic recording recorded at extremely high density in a multi-track state can be simultaneously read by using an optical lens system, and reproduction for each track can be performed by selecting a signal of an optical sensor array. It is also possible. Details of this system can be found in, for example, the 1992 Annual Conference of the Television Society of Japan, MORIS '91 Conference Materials, pp. 389-3
94, IEEE International Conference on Communicati
ons pp. 0110-0114 etc.

Although being practically used as a magneto-optical disk, the absolute magnitude of the magnetic Kerr effect is small. The plane of polarization of the reflected polarized light is TbF which has been put to practical use.
Even the eCo system rotates only about 0.3 degrees. In the magneto-optical disk, this slight rotation of the plane of polarization is detected and extracted as a signal by electronic circuit processing.

[0011]

The reproducing head developed by Thomson Co., Ltd. is capable of forming an extremely fine head core by thin film technology, and also uses a magnetic Kerr effect instead of an electromagnetic conversion coil to transmit light. By carrying out magnetic-electric conversion, electric interaction is removed, and a reproducing head capable of high-density integration is realized. However, the basic principle of magneto-electric conversion by a magneto-optical transducer is
The purpose of this is to detect the change in light intensity caused by the rotation of the plane of polarization due to the magnetic Kerr effect using a polarizing plate with an optical sensor. Therefore, if the magnetic Kerr effect, which is the rotation of the polarization plane of about 0.3 degrees, is used, only a slight change in the light intensity occurs, and the signal-to-noise ratio S / N becomes small.

If the rotation angle of the plane of polarization in the magneto-optical transducer is large, a large S / N is naturally obtained, and further technical possibilities and technological developments are expected. Further, if a large rotation of the polarization plane is obtained, it is not necessary to assist the signal processing technology like an electronic circuit, which was necessary to obtain a sufficient S / N, and naturally cost reduction can be expected.

[0013]

In order to solve this problem, the present invention converts a magnetically recorded magnetic domain pattern change (recording content) into an electrical signal (reproduction signal) through an optical change. In a magnetic recording / reproducing method using magnetic-electrical conversion, the magnetic Faraday effect is characterized in that the direction of the optical axis and the direction of the magnetic flux generated from the recorded magnetic domain have an angle other than perpendicular to each other. The present invention provides a magnetic recording / reproducing method utilizing magnetic-electric conversion according to the present invention. A reproducing head using the magnetic recording / reproducing method, wherein a path of light guided to a magnetic flux guiding magnetic circuit for reproducing the magnetic recording content is arranged to pass through, and a magnetic Faraday constituting the reproducing head. Provided is a reproducing head using iron garnet as an effect material.

The present invention will be described in more detail below. The magneto-optical effect is classified into a magnetic Kerr effect which is a magneto-optical effect on reflected light and a magnetic Faraday effect which is a magneto-optical effect on transmitted light. In general, the magnetic Faraday effect causes a magneto-optical interaction while passing through a magnetic material, and therefore exhibits a significantly large rotation of the polarization plane as compared with the magnetic Kerr effect due to the magneto-optical interaction of only the surface due to reflection. .

The present invention provides a magnetic recording / reproducing method for performing magnetic-electric conversion by utilizing the magnetic Faraday effect in place of the magnetic Kerr effect which exhibits only a small magneto-optical effect as described above, and uses it. It is characterized in that it constitutes a reproducing head.

The magnetic Faraday effect causes rotation of the plane of polarization that is several tens of times greater than the magnetic Kerr effect. By utilizing the magnetic Faraday effect, a reproducing head having a large S / N can be constructed. In the reproducing head having the structure according to the present invention, it is possible to easily increase the S / N as compared with the reproducing head based on the conventional magnetic Kerr effect, and it is possible to obtain the technical possibility and the cost advantage. .

[0017]

The magnetic recording / reproducing method of the present invention, the structure of the reproducing head using the same, and the principle thereof will be described in detail with reference to the drawings. First, the configuration of the magnetic-electrical conversion unit utilizing the magnetic Kerr effect will be described, and the principle thereof will be described in detail. Further, the structure and principle of the magnetic-electric conversion unit utilizing the magnetic Faraday effect, which is a feature of the magnetic recording / reproducing method of the present invention and the reproducing head using the same, will be described in detail.

FIG. 3 shows the structure of a reproducing head utilizing the magnetic Kerr effect, together with magnetically recorded magnetic tape media. The magnetic flux generated from the magnetization recorded on the magnetic tape is
It flows through the magnetic circuit for magnetic flux induction formed in the reproducing head. At this time, the direction of the magnetic flux in the magnetic circuit for magnetic flux guidance also changes according to the direction of the recording magnetization. In a normal reproducing head, such a change in the direction of the magnetic flux flow is electromagnetically converted using a coil and output as an electric signal. Since the electromagnetic conversion coil requires a large volume, it is difficult to construct a multi-track type reproducing head. However, in the magnetic-electric conversion using the magnetic Kerr effect shown in FIG. 3, since the optical system is used as shown in the figure, it is possible to construct a multi-track type reproducing head that is extremely highly integrated. Is.

The principle of magnetic-electric conversion using the magnetic Kerr effect will be described in detail with reference to FIG. Light used for magneto-electric conversion is generated by a laser diode and guided to a magneto-optical transducer through a polarizer optical system. In the magneto-optical transducer, the incident light linearly polarized by the polarizer optical system is guided to the magnetic circuit for magnetic flux guidance, reflected, undergoes the magnetic Kerr effect, and then exits to the analyzer optical system.

The rotation of the polarization plane due to the magnetic Kerr effect changes the light intensity in the analyzer optical system and is converted into an electric signal by the optical sensor. Since the rotation directions of the polarization planes differ by 180 degrees due to the magnetic Kerr effect, the direction of the magnetic flux in the magnetic flux guiding magnetic circuit, that is, the direction of the magnetically recorded magnetization is output as it is as a signal converted as an electrical signal.

The relationship between the magnetization direction of the magnetically recorded magnetic domain, that is, the direction of the magnetic flux passing through the magnetic circuit for magnetic flux induction and the rotation direction of the polarization plane due to the magnetic Kerr effect is as shown in FIG. The rotation direction of the polarization plane due to the magnetic Kerr effect with respect to the magnetic flux directions A and B shown in FIG. 3 is defined as rotating to the right in the A state, and FIG. 2 is shown. The relationship between the direction of magnetization and the direction of light has no meaning in the present invention. The rotation direction changes depending on the material system exhibiting the magnetic Faraday effect. However, if the magnetic flux direction is reversed, the plane of polarization is reversed in any material system. The magnetic recording / reproducing method and the reproducing head of the present invention utilize the correspondence between the reversal of the magnetic flux direction and the reversal of the polarization plane rotation direction due to the magnetic Faraday effect.

It is a known fact that the magnetic Faraday effect exhibits a very large rotation of the plane of polarization as compared to the magnetic Kerr effect. It is obvious that a reproducing head with higher sensitivity and lower noise can be constructed by using the magnetic Faraday effect instead of the magnetic Kerr effect. However, considering the use of the magnetic Faraday effect based on the technology of the magneto-optical disk, the separation type head is necessary in contrast to the magnetic Kerr effect which has been developed, used and commercialized as the technology of the magneto-optical disk. There was a limitation in use due to complication of equipment and inevitability of high cost.

Considering the use of the magnetic Faraday effect as a magnetic sensor such as a reproducing head devised by Thomson, when the magneto-optical disk technology is applied, the magnetic flux vector of the magnetic circuit for magnetic flux guidance and the direction of light are perpendicular to each other. Since it is arranged, the polarization plane does not rotate. That is, when the magnetic flux flows in the film surface direction of the magnetic Faraday effect material formed in a thin film shape, the vector of the magnetic flux and the vector of the light are orthogonal to each other.
In the magneto-optical disk, a perpendicularly magnetized thin film is used as a magnetic recording medium so that the vector of magnetization and magnetic flux and the vector of light are parallel / anti-parallel. FIG. 4 shows the relationship between the magnetic flux vector and the light direction when the magnetic circuit for magnetic flux induction of the Thomson reproducing head and the light direction are arranged perpendicular to each other. As can be seen from FIG. 4, when the light direction and the magnetic flux vector are orthogonal to each other, the magnetic flux vector in the light direction becomes zero, so that the magnetic Faraday effect is not exhibited.

By the present inventor, Japanese Patent Application No. 4-17454
No. 7 "Magnetic Optical Effect Element", Japanese Patent Application No. 4-329276 "Opto-Magnetic Recording Medium and Information Reproducing Method for Handling It"
There is an idea to use the magnetic Faraday effect by the magnetic flux vector in the medium direction as shown in. The idea is to set the magnetic flux vector in the medium and the direction of the light to be non-vertical. The magnetic Faraday effect cannot be clearly observed because the polarization plane is disturbed simply by setting the light direction to something other than vertical. Regarding the observation of the magnetic Faraday in an actual oblique arrangement, “Dependence of Faraday rotation angle on incident angle of light in Bi-YIG thin film”, IEICE, J76-C-II, pp. 484-485
(1993), "Read-out characteristics of in-plane magnetization Bi-YIG thin film by oblique incidence", Journal of Japan Society of Applied Magnetics 17, pp. 1
57-160 (1993), it is necessary to precisely set the angle of the polarization plane, the polarizer and the analyzer. From the above documents, it is clear that the magnetic Faraday effect by the magnetic flux vector in the medium direction can be used.

FIG. 5 shows an example of the structure of a reproducing head for magnetic-electric conversion using the magnetic Faraday effect, instead of the reproducing head developed by Thomson Co., which utilizes the magnetic Kerr effect. The path of light to the magnetic circuit for magnetic flux guidance differs from that of FIG. FIG. 5 shows an example of the structure of the reproducing head utilizing the magnetic Faraday effect. The magnetic Faraday effect is an effect on transmitted light, and if the arrangement is such that light is transmitted, the effect is exactly the same. There are various possible configurations.

FIG. 6 shows a correspondence diagram of the direction of magnetic flux passing through the magnetic circuit for magnetic flux induction, that is, the direction of magnetically recorded magnetic domains and the rotation direction of the polarization plane due to the magnetic Faraday effect. The waveform is exactly the same as that when the magnetic Kerr effect shown in FIG. 2 is used. The vertical axis in the figure varies depending on each magneto-optical material, but the magnitude of rotation of the polarization plane when the magnetic Faraday effect is used is several ten times or more that of the magnetic Kerr effect. Therefore, the S / N can be easily improved.

Since the magnetic Faraday effect shows an extremely large value as compared with the magnetic Kerr effect, the reproducing head utilizing the magnetic Faraday effect shows an extremely good S / N output of its electric signal. It is considered that thin film media will be used more and more in the future due to the demand for high-density recording, which is always required for magnetic recording, but a reproducing head with a good S / N has a greater degree of freedom in media research. And there is no disadvantageous factor. If an S / N margin can be obtained in the reproducing head, it will also be possible to use recording materials and techniques that are considered to be unusable at present. It is also advantageous in production technology. By using the magnetic recording / reproducing method of the present invention and the reproducing head using the magnetic recording / reproducing method, a magnetic recording / reproducing system and a reproducing head exhibiting a magnetic-electric conversion efficiency that is several tens of times higher than that of the conventional case can be constructed. it can.

The magnetic Faraday effect is an effect on transmitted light. Therefore, there is a need for a magnetic Faraday effect material that has good transparency to light. Currently, iron garnet is actively studied as a light-transmitting magnetic material. Usually, in order to obtain a large magneto-optical effect, an iron garnet-based material substituted with an element such as bismuth is used.
The present invention is in no way limited to these material systems. The effect of the present invention is not impaired by any material as long as it is a magnetic Faraday effect material that transmits light. The main part of the present invention is to construct the magneto-optical transducer by the magnetic Faraday effect, and does not depend on the material.

[0029]

EXAMPLE An example of the present invention will be described below. First, a trial production of a reproducing head using the present invention will be described. And
A reproduction experiment using a prototype reproduction head will be described.

FIG. 7 shows the reproducing head manufacturing process. Less than,
This will be described in detail with reference to the drawings. In the trial production, a thin film was formed by using the sputtering method. In addition, soft magnetic iron garnet was used as the magnetic circuit material for magnetic flux induction. The magnetic garnet was crystallized by depositing it in a predetermined composition by a sputtering method and then heat treating it in air.

FIG. 8 shows a sputtering mask pattern used for manufacturing the magnetic circuit for magnetic flux induction. A magnetic garnet polycrystalline film, which is a soft magnetic material, was formed on a quartz glass substrate having a thickness of 0.5 mm. Films were formed to a thickness of 3.5 μm using the mask (A) and 0.5 μm using the mask (B). The target used for the magnetic garnet thin film deposition was oxide powder of F
e ₂ O ₃ : Y ₂ O ₃ : Bi ₂ O ₃ = 4: 2: 1 was mixed and mixed and sintered and used. The sputtering conditions are normal rf sputtering, Ar gas, about 0.1 Torr, and applied power 4
The film thickness was adjusted according to the sputtering time. Since the deposited thin film is amorphous, it was crystallized by heating at 680 ° C. for 5 hours in a general electric furnace to obtain a garnet polycrystalline thin film. The obtained iron garnet thin film had a saturation magnetization of about 100 emu / cm ³ and a coercive force of about 10 Oe.

The magnetic circuit thin film for magnetic flux induction thus prepared was applied to about 5
A 0 μm thick plastic sheet was sandwiched and adhered by an optical adhesive. FIG. 9 shows a cross-sectional configuration diagram after adhesion. As shown in the figure, a magnetic circuit for magnetic flux induction is formed in a portion sandwiched by quartz glass.

Next, the entire magnetic circuit for magnetic flux induction was molded with an optical resin, and the periphery was polished and molded to produce a magneto-optical transducer having the structure shown in FIG.

The magnetic circuit for magnetic flux induction and the materials used in the magneto-optical transducer manufacturing steps or the materials used in the manufacturing may be made of any material as long as the optical characteristics or the chemical characteristics allow. That is, any material can be used as long as the chemical characteristics of the resin do not basically affect the magnetic Faraday effect of the present reproducing head. In general, it is clear that non-magnetic materials have no effect on magnetic properties such as the magnetic Faraday effect.
The magnetic Faraday effect is not affected by the molding process or the like. Therefore, any processing is possible and any molding material can be used, provided the optical properties allow.

The head surface of the obtained reproducing head, which comes into contact with the magnetic tape, was precision-polished to prepare a reproducing head.
Next, the laser diode, the polarizer optical system (polarizing plate), the analyzer optical system (polarizing plate), and the optical sensor were bonded and processed. In this prototype, the lens system was omitted, and light was directly incident from the polished surface of the mold and detected by a direct optical sensor. FIG. 10 is a cross-sectional layout diagram showing the structure of a prototype reproducing head.

The prototype reproducing head was incorporated into a commercially available VTR device for home use, and magnetic recording which was digitally recorded was reproduced by an ordinary ring head. For magnetic recording, a dedicated head in which a 100-turn coil was formed on a sendust head core having a head gap of 3 μm and a track width of 9 mm was used. The recording current was about 1 amp. By controlling the frequency of the function generator given as the recording frequency, digital magnetic recording was performed so that the recording wavelength (length of the recording magnetic domain) was approximately 10 μm.

Reproduction was performed by using the reproducing head which manufactured the tape on which this digital magnetic recording was performed. FIG. 11 shows the direction of magnetically recorded magnetization, that is, the waveform of the recording signal used for magnetic recording and the waveform of the output signal detected by the reproducing head. In this measurement, the analyzer was installed at an angle of about 3 degrees with respect to the polarizer. The analyzer optical system was set to the optimum state in this measurement, that is, the change in the light intensity was maximized.The settings of these optical systems, etc. are the laser type, the magnetic Faraday material type, and various settings of the magneto-optical transducer. Etc., and correlate with each other. Precise alignment is required for measurement.

It can be seen from FIG. 11 that the output waveform of the optical sensor is obtained as an electric signal corresponding to the magnetically recorded magnetization direction. That is, it is shown that the change of the magnetization direction pattern magnetically recorded by the reproducing head, that is, the magnetic recording content can be detected. The S / N of the signal waveform obtained in this example was about 52 dB. Even better S / N could be measured as compared with the S / N of magneto-optical disks currently on the market.

As shown in the above embodiments, it is possible to reproduce the magnetic recording contents by using the reproducing head utilizing the magnetic Faraday effect. The magnetic Faraday effect used in the present reproducing head causes an extremely large rotation of the polarization plane as compared with the magnetic Kerr effect.

[0040]

According to the magnetic recording / reproducing method and reproducing head utilizing the magnetic Faraday effect of the present invention, an extremely large S / N can be easily obtained as compared with the reproducing head utilizing the magnetic Kerr effect developed by Thomson. It becomes possible. If the magnetic recording / reproducing method according to the present invention exhibiting a large S / N and the reproducing head using the same are used, the conventional S
This is advantageous in terms of cost because electronic circuit post-processing such as a filter circuit and an amplifier circuit for improving / N is unnecessary. It is also advantageous in terms of production technology. Further, it is possible to greatly expand the technical possibilities such as a magnetic recording medium using a material which is difficult to use with the conventional magnetic recording / reproducing method and reproducing head.

[0041]

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating the principle of a digital VTR system developed by Thomson, France.

FIG. 2 is an explanatory diagram showing a correspondence relationship between a magnetic recording signal and a rotation direction of a polarization plane due to a magnetic Kerr effect.

FIG. 3 is an explanatory diagram showing the structure and principle of a reproducing head used in a digital VTR system developed by Thomson, France.

FIG. 4 is an explanatory diagram showing the positional relationship between the magnetic flux vector and the direction of light when considered based on the magneto-optical disk technology.

FIG. 5 is an explanatory diagram showing a configuration of a reproducing head utilizing the magnetic Faraday effect according to the present invention.

FIG. 6 is an explanatory diagram showing a correspondence relationship between a magnetic recording signal waveform and a rotation direction of a polarization plane due to the magnetic Faraday effect in a reproducing head using a magnetic recording / reproducing method utilizing the magnetic Faraday effect according to the present invention.

FIG. 7 is an explanatory diagram showing a process of manufacturing a prototype reproducing head in the present embodiment.

FIG. 8 is an explanatory diagram showing a mask pattern used for manufacturing a magnetic circuit for magnetic flux induction.

FIG. 9 is a cross-sectional explanatory diagram for explaining a configuration of a prototype magnetic circuit for magnetic flux induction.

FIG. 10 is a cross-sectional explanatory diagram for explaining the configuration of a prototype reproducing head.

FIG. 11 is an explanatory diagram showing the correspondence between the waveform of the magnetic recording signal and the waveform of the prototype reproducing head output.

Claims (3)

[Claims] 1. A magnetic recording / reproducing method utilizing magnetic-electrical conversion for converting a change (recording content) of a magnetically recorded magnetic domain pattern into an electric signal (reproduction signal) through an optical change. A magnetic recording / reproducing method utilizing magneto-electric conversion by a magnetic Faraday effect, characterized in that an axial direction and a direction of magnetic flux generated from a recorded magnetic domain are arranged at angles other than perpendicular to each other. 2. A reproducing head using the magnetic recording / reproducing method according to claim 1, wherein a light path guided to a magnetic flux guiding magnetic circuit for reproducing the magnetic recording content is arranged to pass therethrough. Characteristic playhead. 3. The reproducing head according to claim 2, wherein iron garnet is used as a magnetic Faraday effect material constituting the reproducing head.