Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-04-11
2004-01-13
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06678128
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exchange coupling film which has an antiferromagnetic layer and a ferromagnetic layer, wherein the direction of magnetization of the ferromagnetic layer is fixed in a predetermined direction by the effect of an exchange magnetic field which is generated at the interface between the antiferromagnetic layer and the ferromagnetic layer. More particularly, the present invention relates to an exchange coupling film which is improved to exhibit a large ratio of resistance variation and also to a magnetoresistive sensor, e.g., a spin valve thin-film device or an ARM device, incorporating such an exchange coupling film, as well as to a thin-film magnetic head which uses such a magnetoresistive sensor.
2. Description of the Related Art
A spin-valve-type thin-film device is a kind of GMR (Giant Magnetoresistive) device which makes use of a giant magnetoresistive effect, and is used for detecting recording magnetic fields from a recording medium such as a hard disk.
The spin-valve-type thin-film device, among various GMR devices, has advantageous features such as simplicity of the structure and high subtlety to vary its magnetic resistance even under a weak magnetic field.
The simplest form of the spin-valve-type thin-film device has an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic intermediate layer, and a free magnetic layer. The antiferromagnetic layer and the pinned magnetic layer are formed in contact with each other, and the direction of the pinned magnetic layer is put into a single magnetic domain state and fixed by an exchange anisotropic magnetic field, which is produced at the interface between the antiferromagnetic layer and the pinned magnetic layer. The magnetization of the free magnetic layer is aligned in a direction which intersects the direction of magnetization of the pinned magnetic layer, by the effect of bias layers that are formed on both sides of the free magnetic layer.
Alloy films such as an Fe—Mn (Iron-Manganese) alloy film, Ni—Mn (Nickel-Manganese) alloy film and a Pt—Mn (Platinum-Manganese) alloy film are generally usable as the material of the antiferromagnetic layer, among which the Pt—Mn alloy film are attracting attention due to its advantages such as a high blocking temperature, superior corrosion resistance, and so forth.
In order to comply with the future demand for higher recording density, it is important to achieve greater exchange coupling magnetic field and greater ratio of resistance variation. However, it has been impossible to obtain a large ratio of resistance variation, with the conventional structure of the magnetoresistive sensor which is composed of an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic intermediate layer and a free magnetic layer.
It has been recognized that the ratio of resistance variation has dependency on exchange coupling magnetic field: the resistance variation ratio decreases unless a large exchange coupling magnetic field is obtained. The resistance variation ratio also has dependency on the crystalline orientations of the layers. With the conventional structure, it has been impossible to obtain a magnetoresistive sensor that possesses both appropriate crystalline orientations and a large exchange magnetic field, and that accordingly exhibits a large resistance variation ratio.
SUMMARY OF THE INVENTION
The present invention is aimed at overcoming these problems, by providing an exchange coupling film having an antiferromagnetic layer, a ferromagnetic layer, and a seed layer formed on the side of the antiferromagnetic layer opposite to the interface between the antiferromagnetic layer and the ferromagnetic layer. The seed layer serves to optimize the crystalline orientations of the layers so as to provide a large ratio of resistance variation. The present invention also provides a magnetoresistive sensor using this exchange coupling film and also a thin-film magnetic head using such a magnetoresistive sensor.
In accordance with a first aspect of the present invention, there is provided an exchange coupling film comprising: an antiferromagnetic layer; a ferromagnetic layer arranged such that an exchange coupling magnetic field is produced at the interface between the antiferromagnetic layer and the ferromagnetic layer; and a seed layer formed on the side of the antiferromagnetic layer opposite to the ferromagnetic layer, the seed layer having face-centered cubic crystals with the (
111
) plane substantially oriented in parallel with the interface; wherein the crystalline structure of at least part of the antiferromagnetic layer comprises CuAu—I type face-centered ordered lattice, wherein the antiferromagnetic layer and the ferromagnetic layer have crystalline orientations in which the (
111
) planes are oriented in parallel with the interface, and wherein a non-aligned crystal lattice state is created at at least part of the interface between the antiferromagnetic layer and the seed layer.
The structure of the exchange coupling film of the present invention has been subjected to a heat treatment after the deposition of the layers constituting the exchange film.
The exchange coupling film of the present invention has the seed layer formed on the side of the antiferromagnetic layer opposite to the interface between the antiferromagnetic layer and the ferromagnetic layer. The seed layer has a crystalline structure composed mainly by face-centered cubic crystals having the (
111
) planes substantially oriented in parallel with the above-mentioned interface. The seed layer thus formed serves to cause the (
111
) planes of the antiferromagnetic layer and the ferromagnetic layer to be in parallel with the interface therebetween, thus offering remarkable improvement in the ratio of resistance variation of a magnetoresistive sensor incorporating the exchange coupling film.
In order to obtain a large exchange coupling magnetic field at the interface between the antiferromagnetic layer and the ferromagnetic layer, a non-aligned state has been created at at least part of the interface between the antiferromagnetic layer and the seed layer. This means that transformation from disordered lattice to ordered lattice has been properly effected, and indicates that an exchange coupling film is obtainable that has a large exchange coupling magnetic field. The ratio of resistance variation has dependency also on the strength of the exchange coupling magnetic field, so that the ratio of resistance variation can be increased as a result of the increase of the exchange coupling.
In accordance with a second aspect of the present invention, there is provided an exchange coupling film comprising: an antiferromagnetic layer; a ferromagnetic layer arranged such that an exchange coupling magnetic field is produced at the interface between the antiferromagnetic layer and the ferromagnetic layer; and a seed layer formed on the side of the antiferromagnetic layer opposite to the ferromagnetic layer, the seed layer having face-centered cubic crystals with the (
111
) plane substantially oriented in parallel with the interface; wherein the crystalline structure of at least part of the antiferromagnetic layer comprises CuAu—I type face-centered ordered lattice, wherein the antiferromagnetic layer and the ferromagnetic layer have crystalline orientations in which the (
111
) planes are oriented in parallel with the interface, and wherein the antiferromagnetic layer and the seed layer have different lattice constants at the interface therebetween.
Unlike the first aspect described before, the second aspect features that the antiferromagnetic layer and the seed layer have different lattice constants at the interface therebetween. Preferably, a crystal lattice non-aligned state is created at at least part of the interface between the antiferromagnetic layer and the seed layer.
In accordance with this aspect of the present invention, the antiferromagnetic layer may be made from an antiferromagnetic alloy material containing an element
Hasegawa Naoya
Ide Yosuke
Saito Masamichi
Tanaka Ken'ichi
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Klimowicz William
LandOfFree
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