Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-04-11
2004-09-14
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S900000, C360S313000, C360S324110
Reexamination Certificate
active
06790541
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. It has been recognized that, when a Pt—Mn alloy film is used as the material of a ferromagnetic layer, the film as deposited has a crystalline structure composed of face-centered cubic lattice in which atoms are positioned in an irregular manner.
In order that a large exchange coupling magnetic field is generated between a ferromagnetic layer and an antiferromagnetic layer after deposition, it is necessary that the crystalline structure of the antiferromagnetic layer be transformed from face-centered cubic lattice as disordered phase to a CuAu—I face-centered square lattice as an ordered phase. Such a transformation can be effected by a heat treatment.
It has been recognized also that a Pt—Mn alloy of bulk type is easily transformed into CuAu—I face-centered square lattice to maximize the antiferromagnetic properties when the ratio of content between Pt and Mn is 50:50 in terms of atomic percent (at %). With this knowledge, the present inventors have made spin valve thin-film device having an antiferromagnetic layer composed of a Pt—Mn alloy, the content ratio between Pt and Mn being set substantially at 50:50, and measured the strength of the exchange magnetic field generated between the antiferromagnetic layer and a ferromagnetic layer. As a result, the inventors found that the strength of the exchange coupling magnetic field is still unsatisfactory, despite the use of the composition ratio between Pt and Mn which is ideal for a bulk phase recrystalization. This is attributable to the fact that the transformation from a disordered lattice to an ordered lattice is still insufficient despite of the heat treatment.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an exchange coupling film capable of generating a large exchange coupling magnetic field when an element X, wherein X is a platinum-group element and Mn comprise an antiferromagnetic layer. A further object is to provide magnetoresistive sensor using such an exchange coupling film and also a thin-film magnetic head incorporating such a magnetoresistive sensor, thereby overcoming the above-described problems of the prior art.
To this end, according to the present invention, there is provided an exchange coupling film comprising: an antiferromagnetic layer; and a ferromagnetic layer in contact with the antiferromagnetic layer such that an exchange coupling magnetic field is produced at the interface between the antiferromagnetic layer and the ferromagnetic layer to fix the magnetization of the ferromagnetic layer in a predetermined direction, wherein the antiferromagnetic layer is made of an antiferromagnetic material containing an element X and Mn, where the element X is from the group of elements consisting of Pt, Pd, Ir, Rh, Ru, and Os, and combinations thereof and combinations thereof, and wherein the crystalline structure of at least part of the antiferromagnetic layer has a CuAu0I type face-centered square ordered lattice.
The exchange film in accordance with the invention is a structure which is obtained through a heat treatment after deposition of the antiferromagnetic layer and the ferromagnetic layer.
One of the features of the present invention is that the antiferromagnetic layer has a region in which the ratio of the atomic percent of the element X to Mn increases towards the ferromagnetic layer. The presence of such a region indicates that the antiferromagnetic layer has been properly transformed from a disordered lattice to an ordered lattice without being restrained by factors, such as the crystalline structure of the ferromagnetic layer, at the interface between the antiferromagnetic layer and the ferromagnetic layer. Thus, the exchange coupling film in accordance with the present invention produces a greater exchange coupling magnetic field than those or the prior art.
The creation of this transformed region results from a production process which will be described later. Thus, in accordance with the present invention, the antiferromagnetic layer has a region in which the ratio of the atomic percent of the element X to Mn increases in a direction towards the ferromagnetic layer, and the crystalline structure of at least part of the antiferromagnetic layer has an ordered lattice. An important factor to these features is the structure of the antiferromagnetic layer as deposited, i.e., in the state prior to the heat treatment.
In accordance with the present invention, the antiferromagnetic layer is formed, for example, as follows. An ordered crystalline structure is readily formed and the antiferromagnetic properties are maximized when the ratio of Pt and Mn is set to 50:50. Such a composition ratio, however, serves to suppress the creation of a non-aligned crystal lattice state at the interface between ferromagnetic layer and the antiferromagnetic layer, resulting in an insufficient transformation from a disordered lattice to an ordered lattice under heat treatment and, hence, insufficient strength of the exchange coupling magnetic field.
Pt contents below about 50 at % tend to hamper transformation into an ordered lattice when heat-treated and, accordingly, make it difficult to achieve satisfactory antiferromagnetic properties. In addition, a strongly aligned crystal lattice state is developed at the interface between the antiferromagnetic layer and the ferromagnetic layer, so that the resultant exchange coupling magnetic field is unacceptably small. Conversely, Pt contents exceeding about 50 at % also hamper transformation to an ordered lattice when the antiferromagnetic layer is formed by heat treatment, so that only very small exchange coupling magnetic field is about 50 at % also hamper transformation to an ordered lattice when
Hasegawa Naoya
Ide Yosuke
Saito Masamichi
Tanaka Ken'ichi
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Falasco Louis
Resan Stevan A.
LandOfFree
Exchange coupling film and electroresistive sensor using the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exchange coupling film and electroresistive sensor using the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exchange coupling film and electroresistive sensor using the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3201903