Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1999-06-04
2002-05-21
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S668000, C428S680000, C428S692100, C428S216000, C360S112000
Reexamination Certificate
active
06391431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistance effect film for reading the magnetic field intensity of a magnetic recording medium or the like as a signal and, in particular, to a magnetoresistance effect film which is capable of reading a small magnetic field change as a greater electrical resistance change signal, and further relates to a magnetoresistance effect type head using such a magnetoresistance effect film. They are mainly incorporated in, for example, hard disk drives so as to be used.
2. Description of the Prior Art
Recently, following the high densification of hard disks, highly-sensitive heads with high outputs have been demanded. In response to these demands, spin valve heads have been developed.
The spin valve head has a structure wherein two ferromagnetic layers are formed via a non-magnetic metal layer, and an antiferromagnetic layer is disposed so as to abut one of the ferromagnetic layers. The ferromagnetic layer abutting the antiferromagnetic layer is in exchange coupling to the antiferromagnetic layer so that the magnetization of the ferromagnetic layer is fixed (pinned) in one direction. The magnetization of the other ferromagnetic layer is freely rotated following the change of the external magnetic field. In the spin valve, the MR change is realized by a difference in relative angles of spins between the two ferromagnetic layers. Therefore, the exchange coupling between the antiferromagnetic layer and the ferromagnetic layer abutting it can be thought as the substance of the spin valve.
As a material of an antiferromagnetic layer used in the spin valve, FeMn, NiMn, PtMn, PtPdMn or the like has been known.
When FeMn is used as the antiferromagnetic layer, the exchange coupling is generated relative to the ferromagnetic layer immediately after the formation of a film. Thus, a heat treatment for generating the exchange coupling is not required after the film formation. However, there is raised a limitation in order of the film formation that the antiferromagnetic layer should be formed after the formation of the ferromagnetic layer. Further, when FeMn is used, there is a problem that a blocking temperature is low, i.e. about 150 to 170° C. The blocking temperature is a temperature at which the exchange coupling pinning a magnetic layer is lost.
On the other hand, when NiMn, PtMn or PtPdMn is used as the antiferromagnetic layer, the blocking temperature is high, i.e. no lower than 300° C., and further, there is no limitation in order of the formation of the antiferromagnetic layer and the ferromagnetic layer. However, for generating the exchange coupling between the antiferromagnetic layer and the ferromagnetic layer, a heat treatment is required in the magnetic field after stacking both layers. This is because, for NiMn, PtMn or PtPdMn to exhibit the antiferromagnetism, a CuAu-I type regular crystal structure having a face centered tetragonal (FCT) structure needs to be formed. The heat treatment in the magnetic field is normally carried out under a temperature condition of 250 to 350° C. The degree of exchange coupling tends to be increased as the temperature is raised. However, if the heat treatment at high temperatures is applied to the spin valve film, a magnetoresistance change ratio (MR ratio) being an important film characteristic of the spin valve film is lowered. Therefore, it is desired that the heat treatment for generating the exchange coupling between the antiferromagnetic layer and the ferromagnetic layer abutting it be carried out at as low a temperature as possible which can achieve the exchange coupling to a given level. Accordingly, proposal for a laminate film structure has been demanded which can realize it.
On the other hand, in case of forming the CuAu-I type regular crystal structure through the heat treatment for manifesting the antiferromagnetism of NiMn, PtMn or PtPdMn, it has been considered the optimum condition for obtaining an excellent antiferromagnetic characteristic that (111) crystal surfaces are oriented on the film surface of the antiferromagnetic layer. Specifically, it has been considered among persons skilled in the art that the (111) crystal surface is the best orientation of the antiferromagnetic layer having the CuAu-I type regular crystal structure. In fact, the literature of Japan Applied Magnetism Institution Journal Vol. 22, No. 4-2, pp 501-504 (1998) as the prior art has also confirmed this fact. Specifically, according to the literature, it has been reported that by (111) orienting the PtPdMn antiferromagnetic layer, the anisotropic energy of the PtPdMn antiferromagnetic layer is increased to increase Hua (shift magnetic field).
However, for obtaining a better spin valve film characteristic, it is important to look at the crystal orientation of the antiferromagnetic layer again from the starting point, not based on such a ready-made idea.
The present invention has been made under these circumstances and has an object to provide a magnetoresistance effect film and a magnetoresistance effect type head which are large in exchange coupling energy between a ferromagnetic layer and an antiferromagnetic layer, large in MR ratio and highly excellent in spin valve film characteristic when NiMn or PtMn or an alloy of them is used as the antiferromagnetic layer thereof.
As the prior art literature relevant to the present invention, there are U.S. Pat. No. 5,608,593 and JP-A-9-63021.
U.S. Pat. No. 5,608,593 discloses a spin valve film having a structure wherein a buffer layer made of Cu or NiCr, an antiferromagnetic layer made of FeMn, NiMn or NiCoO and a ferromagnetic layer pinned by the antiferromagnetic layer are formed in the order named on an under layer formed on a substrate. The buffer layer is described to have an adequate microstructure and functions of promoting a phase of the antiferromagnetic layer and preventing mutual diffusion between the under layer and the antiferromagnetic layer. However, only by a simple combination of the buffer layer made of Cu and the antiferromagnetic layer made of NiMn, the foregoing object of the present invention can not be accomplished to a sufficient level.
On the other hand, JP-A-9-63021 discloses a spin valve film having a structure wherein a film obtained by stacking Ta and NiFe is used as an under layer, and an antiferromagnetic layer made of NiMn and a ferromagnetic layer pinned by the antiferromagnetic layer are formed in the order named on the under layer. It is described that Ta of the under layer is used for smoothing the surface, while NiFe of the under layer is used for allowing NiMn to easily form an FCT structure. However, even if the intermediate layer made of NiFe is used as a layer abutting the antiferromagnetic layer, the foregoing object of the present invention can not be accomplished to a sufficient level.
SUMMARY OF THE INVENTION
For solving the foregoing problems, according to one aspect of the present invention, there is provided a spin valve type magnetoresistance effect film comprising a multilayered film including a non-magnetic metal layer, a ferromagnetic layer formed on one surface of the non-magnetic metal layer, a soft magnetic layer formed on the other surface of the non-magnetic metal layer, an antiferromagnetic layer which is formed on a surface of the ferromagnetic layer remote from the other surface thereof abutting the non-magnetic metal layer so as to pin a direction of magnetization of the ferromagnetic layer, and an antiferromagnetization promote layer formed on a surface of the antiferromagnetic layer remote from the other surface thereof abutting the ferromagnetic layer, wherein the antiferromagnetic layer is made of a compound containing Mn and having a CuAu-I type regular crystal structure, the antiferromagnetic layer has a characteristic requiring a heat treatment for generating exchange coupling relative to the ferromagnetic layer, and the antiferromagnetic layer after the heat treatment has a state wherein (110) crystal surfaces are oriented on a film surface of the an
Araki Satoru
Morita Haruyuki
Sano Masashi
Tsuchiya Yoshihiro
Bernatz Kevin M.
Resan Stevan A.
TDK Corporation
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