Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2003-04-21
2004-04-27
Watko, Julie Anne (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06728081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic head and a magnetic disk apparatus. More particularly, this invention relates to a tunnel magnetoresistive effect type magnetic head and a magnetic disk apparatus that uses a magnetic head of this type. A magnetic disk apparatus is usefully used for an electronic computer or an information processing equipment.
2. Description of the Related Art
As high density magnetic recording has become popular, the high sensitivity reproducing magnetic head is expected to be realized. A magnetoresistive effect type magnetic head (MR head) that utilizes the anisotropic magnetoresistive (AMR) effect has been used for such application as the reproducing head. NiFe has been used as the material of the active region of an MR head. The magnetoresistive change rate of this material is approximately 2%, and the realizable recording density is several Gb/in
2
. Furthermore, recently a spin valve type magnetic head (GMR head) that utilizes giant magnetoresistive effect (GMR) effect has been used for such application. A GRM head comprises two ferromagnetic layers and a non-magnetic layer that is interposed between two ferromagnetic layers. In this structure, magnetization of one ferromagnetic layer is fixed, and a high magnetoresistive change rate due to an angle that is made by two magnetization directions of the two ferromagnetic layers. The magnetoresistive change rate of the GMR ranges from approximately 4 to 5%, and the high recording density of several tens Gb/in
2
is realized. However, to improve the recording density more, a magnetic head having higher magnetoresistive change rate is required.
As the magnetoresistive effect sensor having high magnetoresistive change rate as described hereinabove, a magnetoresistive effect film (TMR) that uses a tunnel magnetoresistive effect film having two ferromagnetic layers and a tunnel barrier layer interposed between the two ferromagnetic layers has attracted attentions. The magnetoresistive effect film that uses the tunnel magnetoresistive effect film is expected to be promising for realizing high density recording. A TMR comprising two Fe films and an Al oxide film interposed between two Fe films was reported to have a high magnetoresistive change rate of approximately 18% at a room temperature. For example, “Journal of Magnetism and Magnetic Materials” (Vol. 139, pp 231, 1995) reports the effect of the TMR. Furthermore, Japanese Unexamined Patent Publication No. Hei 4-103014 discloses a spin valve type TMR in which the magnetization direction of one ferromagnetic layer is fixed by disposing an antiferromagnetic layer adjacent to the ferromagnetic layer.
It is the object of the present invention is to provide a magnetoresistive effect sensor having a tunnel magnetoresistive effect film that is operated stably with reduced Barkhausen noise. The background will be described herein under.
Though a current is supplied in the film in-plane direction of a magnetic film in the case of the conventional magnetoresistive effect element, a current is supplied in the film thickness direction in the case of the TMR. A magnetic head structure that is different from the conventional magnetic head structure is required to realize the above-mentioned structure in which a current is supplied in the thickness direction. On the other hand, a TMR has two ferromagnetic layers as in the case of a conventional spin valve structure, and it is necessary to control the ferromagnetic layers magnetically as a matter of course. Furthermore, the element resistance is determined by the size of the element because a current flows in the film thickness direction.
For example, in the case of the hard bias structure that is same as that of the conventional magnetoresistive effect element, a hard magnetic film is disposed on the periphery of the element to control the magnetic domain. Therefore, in the case that this structure is used for the TMR, a current leaks to the hard magnetic film, and it is difficult to supply a current to the active region of the RMR correctly. Furthermore, the tunnel barrier layer that has a very thin thickness is exposed on the active region of the TMR. Therefore, very difficult working technique is required to prevent short-circuit between two ferromagnetic layers in the working on the facing surface. Furthermore, in the case that the track width of as thin as approximately 0.5 &mgr;m, the resistance of a element is as high as several hundreds to several k&OHgr; inevitably.
SUMMARY OF THE INVENTION
To solve the problems described hereinabove, the structure in which a tunnel barrier layer is not exposed is effective different from the conventional structure in which a tunnel barrier layer is exposed on the facing surface. However, in such case, it is required to magnetically control a magnetic flux guide that is served to guide the magnetic flux from the facing surface to the TMR in addition to the ferromagnetic layer of the active region of the TMR as a matter of course. The present invention solves also this problem.
The basic structure of a magnetic head in accordance the first embodiment of the present invention has a magnetoresistive effective sensor provided with a magnetoresistive effect film having a free layer including a ferromagnetic layer the magnetization of which is rotatable corresponding to the external magnetic field, a pair of electrodes for supplying a current in the film thickness direction of the magnetoresistive effect film, and a magnetic flux guide for guiding a magnetic flux from the recording medium surface to the magnetoresistive effect film, wherein the magnetoresistive effect sensor is capable of controlling both the magnetic domain of the free layer and the magnetic domain of the magnetic flux guide together.
The typical example of the present invention involves an embodiment in which a magnetic domain control layer served for applying a bias on the free layer and the magnetic flux guide is disposed in the same plane in order to control the magnetic domain of the free layer of the tunnel magnetoresistive effect film and the magnetic domain of the magnetic flux guide.
Another example of the present invention involves an magnetic head having a magnetoresistive effect sensor provided with a magnetoresistive effect film that is a tunnel type magnetoresistive effect film comprising a free layer including a ferromagnetic layer, a tunnel barrier layer, a fixed layer including a ferromagnetic layer, and an anti-ferromagnetic layer for fixing the magnetization of the fixed layer, a pair of electrodes for supplying a current in the film thickness direction of the magnetoresistive effect film, and a magnetic flux guide for guiding a magnetic flux from the recording medium surface to the magnetoresistive effect film, wherein the magnetoresistive effect film is formed at the position where the magnetoresistive effect film is not disposed on the medium surface and in contact with the magnetic flux guide that extends from the medium surface to the facing surface, a magnetic domain control layer for applying a bias magnetic filed on the magnetic flux guide is laminated, and the magnetic domain of the free layer is also controlled by controlling the magnetic domain of the magnetic flux guide.
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Miyazaki et al., “Giant magnetic tunneling effect in Fe/AI203/Fe junction,”J. Magnetism and Magnetic Materials, 139 (1995), L231-L234.
Arai Reiko
Kawato Yoshiaki
Watanabe Katsuro
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Watko Julie Anne
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