Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
2001-04-11
2003-11-18
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C029S603130, C029S603140, C029S603150
Reexamination Certificate
active
06648985
ABSTRACT:
BACKGROUND
The present invention relates to methods of producing an exchange coupling film having an antiferromagnetic layer and a ferromagnetic layer, wherein the direction of magnetization of the ferromagnetic layer is fixed by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the ferromagnetic layer. More particularly, the present invention relates to methods of producing an exchange coupling film that provides a large ratio of resistance variation, to methods of producing a magnetoresistive sensor (spin-valve-type thin-film device, AMR device), and to methods of producing a thin-film magnetic head using the magnetoresistive sensor.
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, which is used for detecting recording magnetic fields from a recording medium such as a hard disk.
The spin-valve-type thin-film device, relative to other GMR devices, has advantageous features such as simplicity of structure and ability to vary its magnetic resistance even under a weak magnetic field.
The simplest form of the spin-valve-type thin-film device includes 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. The direction of the pinned magnetic layer is aligned in a single magnetic domain state and fixed by an exchange anisotropic magnetic field 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 Fe—Mn (Iron-Manganese) alloy films, Ni—Mn (Nickel-Manganese) alloy films, and Pt—Mn (Platinum-Manganese) alloy films are generally usable materials for the antiferromagnetic layer. Of these, Pt—Mn alloy films are attracting attention for advantages such as a high blocking temperature, superior corrosion resistance, and so forth.
In order to comply with future demand for higher recording density, it is important to achieve greater exchange coupling magnetic fields and greater ratios of resistance variation.
However, it has been impossible to obtain a large ratio of resistance variation with conventional structures of magnetoresistive sensors, which are composed of an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic intermediate layer and a free magnetic layer.
It has been found that the ratio of resistance variation is dependent on exchange coupling magnetic field. The resistance variation ratio decreases unless a large exchange coupling magnetic field is obtained. The resistance variation ratio is also dependent on the crystalline orientations of the layers. It has been heretofore impossible to use conventional structures to obtain a magnetoresistive sensor which possesses both appropriate crystalline orientations and a large exchange magnetic field, and which therefore exhibits a large resistance variation ratio.
SUMMARY
Accordingly, an object of the present invention is to provide methods of producing an exchange coupling film in which a seed layer is provided on the side of an antiferromagnetic layer opposite to the interface between the antiferromagnetic layer and the ferromagnetic layer, so as to optimize the crystalline orientations of these layers. Thus, a greater resistance variation ratio than obtained with conventional devices is achieved. Additional objects are to provide methods of producing a magnetoresistive sensor using the exchange coupling film, and methods of producing a thin-film magnetic head using the magnetoresistive sensor. In accord with the present invention, the above-described problems are overcome.
In accord with the present invention, there is provided a method of producing an exchange coupling film comprising an antiferromagnetic layer, a ferromagnetic layer contacting the antiferromagnetic layer at an interface therebetween, and a seed layer comprising a (111) plane of face-centered cubic crystal, which seed layer contacts the antiferromagnetic layer at an interface therebetween on a side opposite the ferromagnetic layer. The method comprises forming the seed layer such that the (111) plane of face-centered cubic crystal is preferentially oriented in a direction parallel to the direction of the interface between the seed layer and the antiferromagnetic layer, while creating a non-aligned state at at least a part of the interface between the antiferromagnetic layer and the seed layer. The method further comprises effecting a heat-treatment after formation of the layers, so as to develop an exchange coupling magnetic field at the interface between the antiferromagnetic layer and the ferromagnetic layer.
As stated above, in accordance with the present invention, a seed layer contacts the antiferromagnetic layer on a side thereof opposite the interface between the antiferromagnetic layer and the ferromagnetic layer. The layer is constituted mainly by a face-centered cubic crystalline structure in which, prior to heat treatment, the (111) plane is preferentially oriented in a direction parallel to the interface. This allows the (111) plane of the antiferromagnetic layer in contact with the seed layer, and the (111) plane of the ferromagnetic layer which, together with the seed layer, sandwiches the antiferromagnetic layer, to be preferentially oriented in a direction parallel to the interface.
It is possible to enhance the resistance variation ratio of a magnetoresistive sensor by using an exchange coupling film in which the (111) planes of the antiferromagnetic layer and the ferromagnetic layer are preferentially oriented, as described above.
The enhancement of the resistance variation ratio requires that a large exchange-coupling magnetic field be developed at the interface between the antiferromagnetic layer and the ferromagnetic layer. In accordance with the present invention, at least a part of the interface between the layers is executed such that a non-aligned state is created at at least a part of the interface between the antiferromagnetic layer and the seed layer. Such a non-aligned state of the interface between the seed layer and the antiferromagnetic layer permits the antiferromagnetic layer to be adequately transformed from a disordered lattice into an ordered lattice upon heat-treatment. As a result, a large exchange coupling magnetic field and, therefore, an enhanced resistance variation ratio can be achieved.
The present invention also provides a method of producing an exchange coupling film comprising an antiferromagnetic layer, a ferromagnetic layer contacting the antiferromagnetic layer at an interface therebetween, and a seed layer comprising a (111) plane of face-centered cubic crystal, which seed layer contacts the antiferromagnetic layer at an interface therebetween on a side opposite the ferromagnetic layer, the method comprising forming the seed layer such that the (111) plane of face-centered cubic crystal is preferentially oriented in a direction parallel to the direction of the interface between the seed layer and the antiferromagnetic layer, while creating a difference in lattice constant between the antiferromagnetic layer and the seed layer at at least a part of the interface therebetween. The method further comprises effecting a heat-treatment after formation of the layers, so that an exchange coupling magnetic field is developed at the interface between the antiferromagnetic layer and the ferromagnetic layer.
In accordance with the present invention, the antiferromagnetic layer and the ferromagnetic layer have different lattice constants at at least a part of the interface between the antiferromagnetic layer and the seed layer. Preferably, a non-aligned state is created at at least a part of the interfac
Hasegawa Naoya
Ide Yosuke
Saito Masamichi
Tanaka Ken'ichi
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Sheehan John
LandOfFree
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