Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1998-05-28
2002-11-19
Davis, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06483673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetoresistance head for use in magnetic recording devices, VTR's, etc. The invention relates more particularly to a differential detection type magnetoresistance head.
2. Description of the Related Art
In recent years, the trend of recording tracks toward a decreasing width and that of recording wavelengths toward an increasing frequency have been urging magnetic recording devices such as, for example, hard disc devices to use a further improved recording density. When the width of the recording track is decreased, the sensitivity of the read head is required to be further enhanced because the decrease of the track width entails a decrease in the amount of signal magnetic flux from the magnetic recording medium. As read heads endowed with such high sensitivity, the magnetoresistance heads (hereinafter referred to as “MR head”) have been attracting attention.
In the MR heads, the MR heads (GMR heads) of the type using the so-called giant magnetoresistance (hereinafter referred to as “GMR”) and having a large rate of change in resistance as compared with the MR heads of the type using the anisotropic magnetoresistance (hereinafter referred to as “AMR”) are expected to find recognition as magnetic heads promising high read sensitivity in the future.
For the purpose of improving the linear record resolving power with the shield type MR head which currently prevails in the existing MR heads, the interval or gap between the shield layer possessed of high permeability and the MR element must be decreased. In this case, it is extremely difficult to decrease this interval to or even below 0.1 &mgr;m, with maintaining good electric insulation between the shield layer and the MR element. Thus, the shield type MR head has its limit to the improvement of the linear record dissolving power.
As a breakthrough, the so-called dual element type MR head which has two MR elements superposed through the medium of a nonmagnetic intermediate layer has been proposed. This dual element type MR head generates a so-called differential detection type output response by virtue of the phenomenon that it produces a change in the resistance only when the magnetic recording medium applies signal magnetic fields of opposite directions to the two MR elements, whereas it produces no change in the resistance when this medium applies signal magnetic fields of one same direction thereto. The differential detection type MR head has the read resolving power thereof governed by the thickness of the nonmagnetic intermediate layer and, unlike the shield type MR head, requires the two MR elements thereof to be insulated from each other magnetically and not electrically. The differential detection type MR head, therefore, allows the thickness of the nonmagnetic intermediate layer to be notably decreased, for example, to or even below 10 nm. As a result, it is capable of reading an unusually high linear recording density.
Among the conventional differential detection type MR heads is counted the MR head which uses two AMR elements possessing substantially identical magnetoresistance characteristics (MR characteristics). When the AMR elements are used, such operating point bias magnetic fields as rotate their magnetization in opposite directions like about +45° and −45° from the direction of width of the track are applied. The differential detection type MR head can be realized as a result.
It is suspected, however, that the sensitivity obtainable with the conventional differential detection type MR head using AMR elements will prove insufficient in the near future because the inflow of a signal magnetic field (medium magnetic field) to the upper part of the MR element is not attained when the thickness of the nonmagnetic intermediate layer is decreased. Further, since this MR head necessitates application of the operating point bias magnetic field of the nature mentioned above, it has the problem of encountering difficulty in the impartation and the adjustment of the magnetic field.
The differential detection type MR head using AMR elements is generally constructed by superposing two AMR layers through the medium of a nonmagnetic intermediate layer and forming a pair of electrodes for the supply of a sense current on the upper AMR layer. For the AMR elements in this construction, the angles between the currents and the magnetization constitute themselves an important factor. In order to equalize substantially the MR characteristics of the two AMR elements in the differential detection type MR head, therefore, it is necessary that the characteristics of the two AMR layers themselves be rendered uniform and no angle be formed in the directions of sense currents supplied between the two AMR layers. In the case of the construction in which the electrodes are formed as superposed on one of the AMR layers as described above, the upper and the lower AMR layer produce a difference in the current distribution (as in direction) and the directions of sense currents between these two AMR layers are liable to form an angle. Even when magnetic fields of identical directions are applied to the two AMR layers, therefore, the possibility ensues that the resistance will be varied and this variation will be emitted in the form of a signal. The accidental detection of this erroneous signal possibly results in generation of noise.
Since the conventional differential detection type MR head uses two AMR elements as described above, it entails the problem of readily degrading the sensitivity thereof owing to the fact that the depth of permeation of a signal magnetic field decreases and the fact that the directions of currents between the two AMR layers are inclined toward each other and also the problem of complicating the impartation and the adjustment of the operating point bias magnetic field.
SUMMARY OF THE INVENTION
An object of this invention, therefore, is to provide a differential detection type magnetoresistance head which not only possesses improved line resolving power (read resolving power) but also realizes high sensitivity and high S/N ratio under high reliability.
The magnetoresistance head of the present invention is a differential detection type magnetoresistance head which comprises a magnetoresistance element having a laminated structure comprising at least one pair of ferromagnetic layers and an intermediate layer interposed between the pair of ferromagnetic layers and formed of either a nonmagnetic intermediate layer or a granular type ferromagnetic intermediate layer separated into a magnetic region and a nonmagnetic region, the magnetoresistance element part permitting the resistance thereof substantially varied when signal magnetic fields of mutually opposite directions are applied to the pair of ferromagnetic layers, characterized in that the signal magnetic fields are detected by utilizing the variation of resistance based on the giant magnetoresistance due to the spin-dependent scattering in the magnetoresistance element part.
The nonmagnetic intermediate layer as used in the present invention excludes that which is formed of an antiferromagnetic material as well as that which is formed of a ferromagnetic material.
The differential detection type MR head of this invention can be broadly divided into the following three forms. The first form is such that a laminated structure comprising a pair of ferromagnetic layers excelling in the spin-dependent scatting ability (hereinafter referred to as “GMR ferromagnetic layer”) and a nonmagnetic intermediate layer interposed between the pair of GMR ferromagnetic layers and possessed of low resistance fit for spin-dependent scattering (hereinafter referred to as “GMR nonmagnetic intermediate layer”) is caused to function as a magnetoresistance element part exhibiting a giant magnetoresistance due to the spindependent scattering (hereinafter referred to as “GMR element part”).
The second form is such that a laminated structure comprising at least three ferromagnetic layers and nonm
Akiyama Junichi
Fuke Hiromi
Funayama Tomomi
Hashimoto Susumu
Iwasaki Hitoshi
Davis David
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
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