Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1998-09-28
2003-07-22
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06597547
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistance effect device which causes a substantial magnetoresistance change with a low magnetic field, a magnetoresistance head incorporating the same which is suitable for use in high density magnetic recording and reproduction, and a method for producing a magnstoresistance effect device.
2. Description of the Related Art
A magnetoresistance sensor (hereinafter, referred to simply as an “MR sensor”) and a magnetoresistance head (hereinafter, referred to simply as an “MR head”) employing a magnetoresistance effect device (hereinafter, referred to simply as an “MR device”) have been developed and used in practice. For a magnetic body in the MR device, typically, an Ni
0.8
Fe
0.2
parmalloy film or an Ni
0.8
Co
0.2
alloy film is used. When using such a magnetoresistance effect material, the resulting magnetoresistance rate of change (hereinafter, referred to simply as an “MR ratio”) is about 2%. A larger MR ratio has been desired for an MR device with a higher sensitivity. Recently, it has been found that an [Fe/Cr] or [Co/Ru] artificial grating film which is antiferromagnetically connected via a metallic, non-magnetic thin film such as a Cr film or an Ru film exhibits a large resistance change of substantially 100% (giant magnetoresistance effect) under a strong magnetic field (about 1 to 10 kOe) (Physical Review Letter, Vol. 61, p. 2472 (1988); Physical Review Letter, Vol. 64, p. 2304 (1990)). However, such an artificial grating film requires a strong magnetic field of several kOe to several tens of koe to obtain a large MR change, and thus is not very practical for use in a magnetic head, or the like.
A spin valve type film where an antiferromagnetic material, Fe—Mn, is attached to Ni—Fe/Cu/Ni—Fe has also been proposed (Journal of Magnetism and Magnetic Materials 93, p. 101, (1991)), which is capable of operating under a slight magnetic field. In such a spin valve film, a ferromagnetic film (pin layer) in contact with the ferromagnetic material is provided with a unidirectional anisotropy through an exchange connection, whereby the magnetization direction of the ferromagnetic film is fixed in a certain direction. On the other hand, the magnetization direction of the ferromagnetic layer (free layer), which is provided via the pin layer and a non-magnetic layer, can be changed relatively freely in response to an external signal magnetic field. Therefore, the respective magnetization directions of the pin layer and the free layer change with respect to each other, thereby varying the electric resistance. The necessary operating magnetic field of such an MR material is small, and, the linearity thereof is also good. However, the MR ratio of such an MR material is as low as about 2%, and the Fe—Mn film has a poor corrosion resistance. Moreover, since the Neel temperature of the Fe—Mn film is low, the device characteristics are substantially dependent upon temperature.
It has been proposed to use an oxide antiferromagnetic body such as NiO (Nihon Oyo Jiki Gakkaishi 18, p. 355 (1994)) or &agr;-Fe
2
O
3
(Japanese Laid-open Publication Nos. 8-279117 and 9-92904) as the antiferromagnetic body used in a spin valve film. A spin valve film employing an NiO film has an MR ratio of about 4% to 5% which is greater than that of a spin valve film employing Fe—Mn. However, such a spin valve film has not been used in practice since it is difficult to produce, and the heat stability of an exchange bias magnetic field thereof is poor. In the case of a spin valve film employing &agr;-Fe
2
O
3
, the unidirectional anisotropy in the pin layer is weak, and the coercive force thereof is large. Therefore, such a spin valve film is likely to be a coercive force difference type spin valve film. Moreover, a sufficient MR ratio cannot be obtained unless the film is subjected to a heat treatment after the deposition.
Another type of spin valve having a structure such as Ni—Fe/Cu/Co—Pt and utilizing the coercive force difference between a hard magnetic film and a soft magnetic film has also been proposed, where a hard magnetic material (e.g., Co—Pt) is used in place of the antiferromagnetic material. In such a case, magnetization parallelism or magnetization antiparallelism is created by rotating the magnetization direction of the soft magnetic film (Ni—Fe film) by using a coercive force less than that required for a hard magnetic film. However, this type of spin valve has not been used in practice, since it is difficult to improve the characteristics of the soft magnetic layer.
As described above, the conventional spin valve type MR device does not have a sufficient MR ratio. The conventional spin valve employing NiO provides a high MR ratio, but has problems such as a poor heat stability, a undesirable hysteresis of the MR curve, and an insufficient pinning magnetic field. In the case of the other conventional spin valve film &agr;-Fe
2
O
3
, the MR ratio is lower than that of the spin valve film employing Nio, and a sufficient MR ratio cannot be obtained unless the film is subjected to a heat treatment after the deposition.
SUMMARY OF THE INVENTION
According to one aspect of this invention, a magnetoresistance effect device of the present invention includes a multilayer film. The multilayer film includes an antiferromagnetic film, a first ferromagnetic film, a non-magnetic film and a second ferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The antiferromagnetic film includes an &agr;-Fe
2
O
3
film. A surface roughness of the multilayer film is about 0.5 nm or less.
In one embodiment of the invention,
2
, the first ferromagnetic film includes a Co
1−x
Fe
x
alloy film (0<x≦0.5, where x denotes an atomic composition ratio).
In one embodiment of the invention, the first ferromagnetic film is formed by providing a Co
1−x
Fe
x
alloy layer (0<x≦0.5, where x denotes an atomic composition ratio) on an Ni—Fe alloy layer or an Ni—Fe—Co alloy layer.
In one embodiment of the invention, a main component of the underlying layer is Pt or Au.
In one embodiment of the invention, a thickness of the &agr;-Fe
2
O
3
film is in a range between about 5 nm and about 40 nm.
In one embodiment of the invention, an easy axis of the second ferromagnetic film is arranged so as to be substantially. perpendicular to a direction of a signal magnetic field to be detected.
According to another aspect of this invention, a magnetoresistance effect device includes a multilayer film. The multilayer film includes an antiferromagnetic film, a first ferromagnetic film, a non-magnetic film and a second ferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The antiferromagnetic film includes a layered structure including an &agr;-Fe
2
O
3
film and a second antiferromagnetic film.
In one embodiment of the invention, the second antiferromagnetic film includes an NiO film or a CoO film.
In one embodiment of the invention, the second antiferromagnetic film is overlying the &agr;-Fez
2
O
3
film
In one embodiment of the invention, the &agr;-Fe
2
O
3
film is overlying the NiO film.
In one embodiment of the invention, an easy axis of the second ferromagnetic film is arranged so as to be substantially perpendicular to a direction of a signal magnetic field to be detected.
According to still another aspect of this invention a magnetoresistance effect device includes a multilayer film. The multilayer film includes an antiferromagnetic film, a first ferromagnetic film, a non-magnetic film and a second ferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The antiferromagnetic film includes an &agr;-Fe
2
O
3
film. A thickness of the &agr;-Fe
2
O
3
film is in a range between about 5 nm and about 40 nm.
In one embodiment of the invention, an easy axis of the second ferromagnetic film is arranged so as to be substantially
Kawawake Yasuhiro
Sakakima Hiroshi
Satomi Mitsuo
Sugita Yasunari
Renner Craig A.
Renner , Otto, Boisselle & Sklar, LLP
LandOfFree
Magnetoresistive device with an &agr;-Fe2O3... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetoresistive device with an &agr;-Fe2O3..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetoresistive device with an &agr;-Fe2O3... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3108821