JP3279081B2 - Signal playback method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal reproducing method for reproducing various information signals written on a magnetic tape or a magnetic disk, and more particularly to a novel signal reproducing method for realizing a high recording density.

[0002]

2. Description of the Related Art To achieve high-density magnetic recording, a magnetic material having a larger coercive force Hc and a large residual magnetization has been used for a magnetic recording medium. Specifically, γFe ₂ O ₃ to Co-γFe ₂ O ₃ , metal magnetic powder,
In the case of Co deposition or a hard disk, the coating type is changed to Co-Ni under Cr, CoCrTa under Co,
Progress has been made in the order of PtCr and the like.

As described above, the recording material of the magnetic recording medium is as follows.
Progress is made in the order of oxide powder → metal powder → metal film. This is because high Br and high Hc were aimed at. On the other hand, in the reproducing head, research is progressing from an inductive type using an induced electromotive force due to a change in medium magnetization to a so-called MR type using a magnetoresistance change, and a part of the reproducing head is being put to practical use.

In the MR type, a reproduction signal is obtained by the magnetization of the medium being induced into a permalloy thin film or the like, and the permalloy electric resistance changing due to the change in the permalloy magnetization. Compared to the inductive type, the MR type provides a large reproduction output even if the area to be changed is extremely small,
Higher sensitivity is achieved, which allows a reduction in the track width of magnetic recording.

[0005]

The MR type magnetic head (MR head) includes a yoke type and a non-yoke type in which an MR permalloy is exposed on a sliding surface. The non-yoke type has a higher read sensitivity. Is said to be high. However, in a non-yoke type MR head, since the MR element is exposed on the medium sliding surface, there is a problem in durability and reliability in a contact type system such as a magnetic tape. In particular, when a metal deposited film having low electric resistance is used for the magnetic layer of the magnetic tape,
Since the MR reproducing current flows to the tape side, the non-yoke type cannot be used.

[0006] In the case of a hard disk, since the magnetic head is levitated from the medium by about 0.1 µm, a non-yoke type MR head can be applied to a magnetic recording medium using a metal deposition film. However, in order to achieve higher density recording, the flying height of the head tends to be reduced, and in this case, the insulating property still becomes a problem. Further, when the track width is further narrowed, there remains a problem in the method of increasing the altitude while preventing the instability of magnetization at both ends of the MR element or Barkhausen noise.

As described above, it is impossible to combine a vapor-deposited tape capable of obtaining a high output with a non-yoke type MR head having a high reproduction sensitivity in a tape system. Problems remain in the development. Therefore, the present invention has been proposed to solve the above-mentioned problems, and it is an object of the present invention to provide a completely novel signal reproducing method capable of achieving high-density recording and having high output and high reliability. With the goal.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a magnetic recording medium in which signals are recorded on a magnetic layer by magnetization reversal. And the direction of magnetization of the magnetic material constituting the electrode is made substantially the same as the direction of one of the reversal magnetizations of the magnetic layer, and the electrical resistance between the magnetic recording medium and the electrode is measured. In the form of a reproduction signal.

In the present invention, a current is passed directly from the electrode to the magnetic recording medium, and a reproduction output is obtained by utilizing the fact that the electric resistance at that time changes due to the consistency of the direction of magnetization between the electrode and the magnetic recording medium. . That is, a magnetic recording medium having a low surface electrical resistance is contacted with or close to the magnetic recording medium, and a magnetization direction in the same direction as the magnetization direction of one of the reversal magnetizations of the magnetic recording medium and opposite to the other magnetization direction. A reproduction signal is obtained by measuring the electric resistance between the medium and the electrode using an electrode which is a hard magnetic material having a low electric resistance.

Here, another electrode is required to allow a current to flow between the magnetic recording medium and the electrode. However, since the electric resistance of the magnetic recording medium is generally high in a metal film, a non-magnetic auxiliary electrode is required. It is desired to be installed near the hard magnetic electrode. Since the electrodes are installed perpendicularly or obliquely to the magnetic recording medium, when the in-plane magnetized film is used for the medium, the perpendicular magnetized film is used for the electrode, and when the perpendicular magnetized film is used for the medium, By using an in-plane magnetized film for the electrode, the direction of magnetization between the electrode and the medium can be matched. If the electrode has a magnetized structure, electrons are scattered, so the electrode needs to have a squareness ratio of 1.

Specifically, for example, as a magnetic recording medium, C
When an o-based alloy oblique deposition tape is used, a perpendicular magnetization film such as a Co-Cr, Co / Pt-based multilayer, a Co-Pd-based multilayer, or CoPtBO is used as an electrode. Co-Cr, Co / Pt based multilayer film, Co-Pd as magnetic recording medium
When using a perpendicular magnetic recording medium such as a Co-based multilayer film or CoPtBO, a Co-based alloy obliquely deposited film or a Cr-based Co
An in-plane anisotropic magnetic film such as a system alloy film is used.

As described above, a hard magnetic material can be used for the electrode. Particularly, in the case of a combination of a perpendicular magnetization medium and an in-plane magnetization electrode, a soft magnetic material such as Permalloy or Sendust is used as an electrode material. When a bias magnetic field is applied to the magnetic field, an in-plane unidirectional magnetization is obtained, and the same effect as that of the hard magnetic material can be obtained. By the way, since a hard magnetic material is used for the electrode, it is necessary to consider the influence of magnetization on the medium due to this. Since the magnetic recording medium has its own demagnetizing ability and there is little difference in the magnetic characteristics between the magnetic recording medium and the electrode, if the electrode has the same thickness as the magnetic recording medium (2000 Å or less), In addition, the electrodes do not influence the magnetization of the medium.

Further, by providing a layer made of a material having a low electric resistance such as Cu, Ag, or Au as a base layer of the magnetic layer of the magnetic recording medium, the electric resistance of the magnetic recording medium is reduced, and It is possible to make the change in the electric resistance between the electrodes relatively large. Furthermore, digital audio tape recorders (so-called S-DAT and DCC)
) And a data recording system (so-called QIC system) use a multi-track fixed head. However, there remains a problem in reducing the track width such as the electrodes of the MR element. The signal reproducing method of the present invention only requires the installation of electrodes and does not require other elements, so that the track pitch can be significantly reduced, and is particularly suitable for a multi-track system.

[0014]

In recent years, research on giant magnetoresistive elements (GMR materials) has revealed that the electric resistance when passing through a magnetic material having a different magnetization direction is higher than when the magnetization directions are aligned. ing. (Journal of the Japan Society of Applied Magnetics Vol16 No4 1
992 See pages 615 to 635) In the case of a GMR head, the G
When the magnetization state inside the MR material changes, the current voltage flowing through the GMR material changes. A reproduction signal is obtained from the change in the current voltage.

As a result of further intensive studies on this phenomenon, the present inventor has come up with a method of more directly extracting a magnetization pattern of a medium as a reproduction signal. That is,
The phenomenon that the electric resistance increases due to the discontinuity of the magnetization direction is not limited to the inside of a multilayer film system such as a GMR material or a spin valve material, but also occurs between a magnetic recording medium and a magnetized electrode. According to these magnetization directions, it is possible to directly extract the magnetization of the medium as an electric resistance without having to guide the magnetization of the medium into the soft magnetic material.

Therefore, by utilizing this phenomenon, it is possible to reproduce a completely new magnetic signal which does not require any soft magnetic material. Here, in the present invention, since a magnetic circuit is not required unlike the related art, it is completely relieved of the head efficiency and the difficulty in designing the head such as the magnetic gap depth which had an influence on the head efficiency, and the electrodes are not required. Since the length can be long, the length of the portion where the head can be cut can be increased. In other words, the life of the head can be greatly increased without the limitation of the gap depth.

Furthermore, since the electrodes are thin and sufficient, multi-tracking is extremely easy as compared with conventional inductive and MR heads.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below in detail with reference to the drawings. Embodiment 1 This embodiment is an example in which an in-plane magnetic recording medium and an electrode made of a perpendicular magnetization film are combined.

As shown in FIG. 1, the magnetic recording medium 1 includes:
A Cu underlayer 12 (thickness 1000 Å) is formed on the nonmagnetic support 11, and a Co-layer is formed thereon by oblique evaporation.
An evaporation tape (M) on which an evaporation film 13 made of a Ni alloy is formed.
E tape). A signal is written on this vapor deposition tape by a normal magnetic head (here, so-called MIG).
Head).

As shown in FIGS. 2 and 3, the reproducing head 2 was formed by forming a CoPtBO perpendicular magnetized magnetic material (200 angstrom thick) on the nonmagnetic insulator 21 as the electrode 22. . The reproducing head 2 has an insulating film 23 (film thickness 20) on the electrode 22 in addition to the electrode 22.
Auxiliary electrode 2 formed through the film
4, which are sandwiched between the non-magnetic insulator 21 and another non-magnetic insulator 25.

The auxiliary electrode 24 is made of Cu and has a thickness of 4000 angstroms. Terminal portions 26 and 27 for connecting to an external circuit are connected to the electrode 22 and the auxiliary electrode 24, respectively. By supplying a sense current between these terminal portions 26 and 27, the auxiliary electrode 24 The sense current flows in the order of → the magnetic recording medium 1 → the electrode 22.

At the time of reproduction, as shown in FIG. 1, the auxiliary electrode 24, the magnetic recording medium 1 (the deposited film 13 and the Cu underlayer 1) are used.
2) passing through the electrode 22, where the electrode 22 and the deposited film 1
The electrical resistance is low when the directions of magnetization of No. 3 coincide with each other, and the electrical resistance increases when they face in opposite directions. This makes it possible to directly reproduce the magnetization pattern without using the leakage magnetic flux from the magnetic recording medium as in the related art.

In practice, when the track width was set to 20 μm and the electric resistance between the electrodes was measured while moving the magnetic tape (magnetic recording medium 1), 5% was obtained when the magnetization directions were the same and opposite. Differences in electrical resistance were observed. Embodiment 2 This embodiment is an example in which a perpendicular magnetization recording medium and an in-plane magnetization film are combined.

The structures of the magnetic recording medium and the reproducing head are the same as those of the previous embodiment, except that the deposited film 1 is formed on the Cu underlayer 12.
As No. 3, a medium in which a Co—Cr perpendicular magnetization film was formed was used as a medium, and a CoPtPO in-plane magnetization film was used as an electrode 22.
FIG. 4 shows a conceptual diagram . As in Example 1, electrodes -
A difference of 5% in electric resistance was observed due to coincidence and inconsistency of the magnetization directions between the media. In a general MR element, a change in electric resistance due to medium magnetization is 1% or less.

Although magnetic properties with a squareness ratio of 1 cannot generally be obtained with a CoPtPO in-plane magnetized medium, in the case of this example, the combination with a shape anisotropy that is thin and long in the longitudinal direction allows the electrode material to be used. As a result, a material having a squareness ratio of 1 without magnetization was obtained. The same applies when permalloy is used for the electrode 22 and a bias magnetic field is applied thereto. Example 3 A multi-track head having a track pitch of 40 μm, a track width of 20 μm and a track number of 20 was experimentally manufactured by using a combination of a magnetic recording medium and a reproducing head having the same structures as those of the previous Example 1. Here, it was found that crosstalk between tracks was not observed at all, and that a multitrack head could be manufactured using only extremely simple electrodes. The change in electric resistance of each track was 5%.

[0026]

As is apparent from the above description, the signal reproducing method of the present invention enables high-sensitivity reproduction with only a very simple structure using only electrodes. Moreover, unlike the MR head, there are no problems such as magnetization control, bias, electrode direction, Barkhausen noise, etc., and crosstalk is extremely small.

Further, since there is no need to form a magnetic circuit, the problem of the head life due to the depth is solved, and the simple structure is particularly suitable for a multi-track head.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the principle of reproduction when an in-plane magnetic recording medium and an electrode composed of a perpendicular magnetization film are combined.

FIG. 2 is a schematic perspective view showing a configuration example of a reproducing head.

FIG. 3 is a schematic sectional view of the reproducing head shown in FIG.

FIG. 4 is a schematic diagram for explaining the principle of reproduction when a perpendicular magnetization recording medium and an electrode composed of an in-plane magnetization film are combined.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Reproducing head 12 Cu underlayer 13 Vapor deposition film 22 Electrode 24 Auxiliary electrode

Claims (8)

(57) [Claims] An electrode made of a magnetic material is brought into contact with or close to a magnetic recording medium in which a signal is recorded on the magnetic layer by magnetization reversal, and the direction of magnetization of the magnetic material constituting the electrode is changed to the magnetic layer. A signal reproducing method which has substantially the same direction as one of the reversal magnetizations, and measures an electric resistance between the magnetic recording medium and the electrode to obtain a reproduction signal. 2. The signal reproducing method according to claim 1, wherein a conductive non-magnetic auxiliary electrode is provided adjacent to the electrode made of a magnetic material via an insulating layer. 3. The signal reproducing method according to claim 1, wherein the magnetic recording medium is a magnetic recording medium having an in-plane magnetization film as a recording layer, and the electrodes are perpendicular magnetization films. 4. The signal reproducing method according to claim 1, wherein the magnetic recording medium is a magnetic recording medium having a perpendicular magnetization film as a recording layer, and the electrodes are in-plane magnetization films. 5. The signal reproducing method according to claim 1, wherein the thickness of the electrode is less than 2000 Å. 6. The signal reproducing method according to claim 1, wherein a magnetic layer is formed on the conductive underlayer. 7. The signal reproducing method according to claim 1, wherein a plurality of electrodes are arranged in a track width direction to perform multi-track reproduction. 8. The signal reproducing method according to claim 1, wherein the magnetic recording medium is a perpendicular magnetization film, the electrode is a soft magnetic thin film, and a bias magnetic field is applied to the soft magnetic thin film to form an in-plane unidirectional magnetization film.