U.S. patent application number 10/386343 was filed with the patent office on 2003-08-21 for magnetoresistance effect device, magnetoresistance head and method for producing magnetoresistance effect device.
Invention is credited to Kawawake, Yasuhiro, Sakakima, Hiroshi, Satomi, Mitsuo, Sugita, Yasunari.
Application Number | 20030156360 10/386343 |
Document ID | / |
Family ID | 17386347 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030156360 |
Kind Code |
A1 |
Kawawake, Yasuhiro ; et
al. |
August 21, 2003 |
Magnetoresistance effect device, magnetoresistance head and method
for producing magnetoresistance effect device
Abstract
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 comprises an
.alpha.-Fe.sub.2O.sub.3 film. A surface roughness of the multilayer
film is about 0.5 nm or less.
Inventors: |
Kawawake, Yasuhiro; (Osaka,
JP) ; Satomi, Mitsuo; (Osaka, JP) ; Sugita,
Yasunari; (Osaka, JP) ; Sakakima, Hiroshi;
(Kyotanabe-shi, JP) |
Correspondence
Address: |
Thomas W. Adams
Renner, Otto, Boisselle, & Sklar, L.L.P.
1621 Euclid Avenue, 19th Floor
Cleveland
OH
44115
US
|
Family ID: |
17386347 |
Appl. No.: |
10/386343 |
Filed: |
March 11, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10386343 |
Mar 11, 2003 |
|
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|
09162300 |
Sep 28, 1998 |
|
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Current U.S.
Class: |
360/324.11 ;
204/192.34; 257/E43.005; G9B/5.114; G9B/5.124; G9B/5.135 |
Current CPC
Class: |
B82Y 25/00 20130101;
G11B 2005/3996 20130101; H01L 43/10 20130101; G11B 5/3903 20130101;
G11B 5/3932 20130101; B82Y 10/00 20130101; G11B 5/3967 20130101;
H01F 10/3268 20130101 |
Class at
Publication: |
360/324.11 ;
204/192.34 |
International
Class: |
G11B 005/39 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 1997 |
JP |
9-263212 |
Claims
What is claimed is:
1. A magnetoresistance effect device, comprising a multilayer film,
the multilayer film comprising 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, wherein: the antiferromagnetic
film comprises an .alpha.-Fe.sub.2O.sub.3 film; and a surface
roughness of the multilayer film is about 0.5 nm or less.
2. A magnetoresistance effect device according to claim 1, wherein
the first ferromagnetic film comprises a Co.sub.1-xFe.sub.x alloy
film (0<x.ltoreq.0.5, where x denotes an atomic composition
ratio).
3. A magnetoresistance effect device according to claim 1, wherein
the first ferromagnetic film is formed by providing a
Co.sub.1-xFe.sub.x alloy layer (0<x.ltoreq.0.5, where x denotes
an atomic composition ratio) on an Ni--Fe alloy layer or an
Ni--Fe--Co alloy layer.
4. A magnetoresistance effect device according to claim 1, wherein
a main component of the underlying layer is Pt or Au.
5. A magnetoresistance effect device according to claim 1, wherein
a thickness of the .alpha.-Fe.sub.2O.sub.3 film is in a range
between about 5 nm and about 40 nm.
6. A magnetoresistance effect device according to claim 1, wherein
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.
7. A magnetoresistance effect device, comprising a multilayer film,
the multilayer film comprising 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, wherein: the antiferromagnetic
film comprises a layered structure including an
.alpha.-Fe.sub.2O.sub.3 film and a second anti-ferromagnetic
film.
8. A magnetoresistance effect device according to claim 7, wherein
the second antiferromagnetic film comprises an NiO film or a CoO
film.
9. A magnetoresistance effect device according to claim 7, wherein
the second antiferromagnetic film is overlying the
.alpha.-Fe.sub.2O.sub.3 film.
10. A magnetoresistance effect device according to claim 7, wherein
the .alpha.-Fe.sub.2O.sub.3 film is overlying the NiO film.
11. A magnetoresistance effect device according to claim 7, wherein
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.
12. A magnetoresistance effect device, comprising a multilayer
film, the multilayer film comprising 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,
wherein: the antiferromagnetic film comprises an
.alpha.-Fe.sub.2O.sub.3 film; and a thickness of the
.alpha.-Fe.sub.2O.sub.3 film is in a range between about 5 nm and
about 40 nm.
13. A magnetoresistance effect device according to claim 12,
wherein 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.
14. A magnetoresistance effect device, comprising a multilayer
film, the multilayer film comprising a first antiferromagnetic
film, a first ferromagnetic film, a first non-magnetic film, a
second ferromagnetic film, a second non-magnetic film, a third
ferromagnetic film and a second antiferromagnetic film, which are
provided in this order on a non-magnetic substrate directly or via
an underlying layer, wherein: the first antiferromagnetic film
comprises an .alpha.-Fe.sub.2O.sub.3 film; and a surface roughness
of the multilayer film is about 0.5 nm or less.
15. A magnetoresistance effect device according to claim 14,
wherein 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.
16. A magnetoresistance effect device, comprising a multilayer
film, the multilayer film comprising a first antiferromagnetic
film, a first ferromagnetic film, a first non-magnetic film, a
second ferromagnetic film, a second non-magnetic film, a third
ferromagnetic film and a second antiferromagnetic film, which are
provided in this order on a non-magnetic substrate directly or via
an underlying layer, wherein: the first antiferromagnetic film
comprises a layered structure including an .alpha.-Fe.sub.2O.sub.3
film and a third antiferromagnetic film.
17. A magnetoresistance effect device according to claim 16,
wherein the second antiferromagnetic comprises an Ir--Mn film.
18. A magnetoresistance effect device according to claim 17,
wherein 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.
19. A magnetoresistance effect device according to claim 16,
wherein at least one of the first ferromagnetic film and the third
ferromagnetic film comprises an indirect exchange coupling
film.
20. A magnetoresistance head, comprising: a magnetoresistance
effect device according to claim 6; and a shield gap section for
insulating the magnetoresistance effect device from a shield
section.
21. A magnetoresistance head, comprising: a magnetoresistance
effect device according to claim 11; and a shield gap section for
insulating the magnetoresistance effect device from a shield
section.
22. A magnetoresistance head, comprising: a magnetoresistance
effect device according to claim 13; and a shield gap section for
insulating the magnetoresistance effect device from a shield
section.
23. A magnetoresistance head, comprising: a magnetoresistance
effect device according to claim 15; and a shield gap section for
insulating the magnetoresistance effect device from a shield
section.
24. A magnetoresistance head, comprising: a magnetoresistance
effect device according to claim 18; and a shield gap section for
insulating the magnetoresistance effect device from a shield
section.
25. A method for producing a magnetoresistance effect device, the
device comprising a multilayer film, the multilayer film comprising
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 method comprising: a first step of forming
the antiferromagnetic film having a thickness in a range between
about 5 nm and about 40 nm on the non-magnetic substrate directly
or via the underlying layer; and a second step of depositing, on
the antiferromagnetic film, the first ferromagnetic film, the
non-magnetic film and the second ferromagnetic film in this order
so that a surface roughness of the multilayer film is about 0.5 nm
or less, wherein the first step comprises a step of sputtering a
target whose main component is .alpha.-Fe.sub.2O.sub.3.
26. A method for producing a magnetoresistance effect device, the
device comprising a multilayer film, the multilayer film comprising
a first antiferromagnetic film, a first ferromagnetic film, a first
non-magnetic film, a second ferromagnetic film, a second
non-magnetic film, a third ferromagnetic film and a second
antiferromagnetic film, which are provided in this order on a
non-magnetic substrate directly or via an underlying layer, the
method comprising: a first step of forming the first
antiferromagnetic film on the non-magnetic substrate directly or
via the underlying layer; a second step of depositing, on the
antiferromagnetic film, the first ferromagnetic film, the first
nonmagnetic film, the second ferromagnetic film, the second
non-magnetic film, the third ferromagnetic film and the second
antiferromagnetic film in this order so that a surface roughness of
the multilayer film is about 0.5 nm or less, wherein the first step
comprises a step of sputtering a target whose main component is
.alpha.-Fe.sub.2O.sub.3.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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 magnetoresistance effect
device.
[0003] 2. Description of the Related Art
[0004] 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.sub.0.8Fe.sub.0.2 parmalloy film or
an Ni.sub.0.8Co.sub.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.
[0005] 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.
[0006] It has been proposed to use an oxide antiferromagnetic body
such as NiO (Nihon Oyo Jiki Gakkaishi 18, p. 355 (1994)) or
.alpha.-Fe.sub.2O.sub.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 .alpha.-Fe.sub.2O.sub.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.
[0007] 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.
[0008] 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 .alpha.-Fe.sub.2O.sub.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
[0009] 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 .alpha.-Fe.sub.2O.sub.3 film. A
surface roughness of the multilayer film is about 0.5 nm or
less.
[0010] In one embodiment of the invention, 2. the first
ferromagnetic film includes a Co.sub.1-xFe.sub.x alloy film
(0<x.ltoreq.0.5, where x denotes an atomic composition
ratio).
[0011] In one embodiment of the invention, the first ferromagnetic
film is formed by providing a Co.sub.1-xFe.sub.x alloy layer
(0<x.ltoreq.0.5, where x denotes an atomic composition ratio) on
an Ni--Fe alloy layer or an Ni--Fe--Co alloy layer.
[0012] In one embodiment of the invention, a main component of the
underlying layer is Pt or Au.
[0013] In one embodiment of the invention, a thickness of the
.alpha.-Fe.sub.2O.sub.3 film is in a range between about 5 nm and
about 40 nm.
[0014] 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.
[0015] 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 .alpha.-Fe.sub.2O.sub.3
film and a second antiferromagnetic film.
[0016] In one embodiment of the invention, the second
antiferromagnetic film includes an NiO film or a CoO film.
[0017] In one embodiment of the invention, the second
antiferromagnetic film is overlying the .alpha.-Fe.sub.2O.sub.3
film.
[0018] In one embodiment of the invention, the
.alpha.-Fe.sub.2O.sub.3 film is overlying the NiO film.
[0019] 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.
[0020] 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 .alpha.-Fe.sub.2O.sub.3 film. A thickness of the
.alpha.-Fe.sub.2O.sub.3 film is in a range between about 5 nm and
about 40 nm.
[0021] 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.
[0022] According to still another aspect of this invention, a
magnetoresistance effect device includes a multilayer film. The
multilayer film includes a first antiferromagnetic film, a first
ferromagnetic film, a first non-magnetic film, a second
ferromagnetic film, a second non-magnetic film, a third
ferromagnetic film and a second antiferromagnetic film, which are
provided in this order on a non-magnetic substrate directly or via
an underlying layer. The first antiferromagnetic film includes an
.alpha.-Fe.sub.2O.sub.3 film. A surface roughness of the multilayer
film is about 0.5 nm or less.
[0023] 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.
[0024] According to still another aspect of this invention, a
magnetoresistance effect device includes a multilayer film. The
multilayer film includes a first antiferromagnetic film, a first
ferromagnetic film, a first non-magnetic film, a second
ferromagnetic film, a second non-magnetic film, a third
ferromagnetic film and a second antiferromagnetic film, which are
provided in this order on a non-magnetic substrate directly or via
an underlying layer. The first antiferromagnetic film includes a
layered structure including an .alpha.-Fe.sub.2O.sub.3 film and a
third antiferromagnetic film.
[0025] In one embodiment of the invention, the second
antiferromagnetic includes an Ir--Mn film.
[0026] 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.
[0027] In one embodiment of the invention, at least one of the
first ferromagnetic film and the third ferromagnetic film includes
an indirect exchange coupling film.
[0028] According to still another aspect of this invention, a
magnetoresistance effect device includes a multilayer film. The
multilayer film includes an antiferromagnetic film, an indirect
exchange coupling film, a first non-magnetic film, a first
ferromagnetic film, which are provided in this order on a
non-magnetic substrate directly or via an underlying layer. The
antiferromagnetic film includes an .alpha.-Fe.sub.2O.sub.3 film.
The indirect exchange coupling film includes a second non-magnetic
film and a pair of second ferromagnetic films interposing the
second non-magnetic film therebetween.
[0029] In one embodiment of the invention, a main component of the
second ferromagnetic film is Co.
[0030] In one embodiment of the invention, a main component of the
second non-magnetic film is Ru.
[0031] According to still another aspect of this invention, a
magnetoresistance head includes: a magnetoresistance effect device
as described above; and a shield gap section for insulating the
magnetoresistance effect device from a shield section.
[0032] According to still another aspect of this invention, a
method for producing a magnetoresistance effect device is provided.
The 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 method includes: a first step of forming
the antiferromagnetic film having a thickness in a range between
about 5 nm and about 40 nm on the non-magnetic substrate directly
or via the underlying layer; and a second step of depositing, on
the antiferromagnetic film, the first ferromagnetic film, the
non-magnetic film and the second ferromagnetic film in this order
so that a surface roughness of the multilayer film is about 0.5 nm
or less. The first step includes a step of sputtering a target
whose main component is .alpha.-Fe.sub.2O.sub.3.
[0033] According to still another aspect of this invention, a
method for producing a magnetoresistance effect device is provided.
The device includes a multilayer film, the multilayer film includes
a first antiferromagnetic film, a first ferromagnetic film, a first
non-magnetic film, a second ferromagnetic film, a second
non-magnetic film, a third ferromagnetic film and a second
antiferromagnetic film, which are provided in this order on a
non-magnetic substrate directly or via an underlying layer. The
method includes: a first step of forming the first
antiferromagnetic film on the non-magnetic substrate directly or
via the underlying layer; a second step of depositing, on the
antiferromagnetic film, the first ferromagnetic film, the first
non-magnetic film, the second ferromagnetic film, the second
non-magnetic film, the third ferromagnetic film and the second
antiferromagnetic film in this order so that a surface roughness of
the multilayer film is about 0.5 nm or less. The first step a step
of sputtering a target whose main component is
.alpha.-Fe.sub.2O.sub.3.
[0034] Thus, the invention described herein makes possible the
advantages of: (1) providing an MR device which exhibits a large MR
ratio by using an .alpha.-Fe.sub.2O.sub.3 film or an
.alpha.-Fe.sub.2O.sub.3/NiO layered film so as to precisely control
the surface roughness of the interface; (2) providing a method for
producing such an MR device; and (3) providing an MR head
incorporating such an MR device.
[0035] These and other advantages of the present invention will
become apparent to those skilled in the art upon reading and
understanding the following detailed description with reference to
the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1A is a cross-sectional diagram illustrating a
structure of an MR device of the present invention;
[0037] FIG. 1B is a cross-sectional diagram illustrating a
structure of an MR device of the present invention;
[0038] FIG. 2A is a cross-sectional diagram illustrating a
structure of an MR device of the present invention;
[0039] FIG. 2B is a cross-sectional diagram illustrating a
structure of an MR device of the present invention;
[0040] FIG. 3 is a cross-sectional diagram illustrating a structure
of an MR head of the present invention;
[0041] FIG. 4 is a perspective view illustrating the MR head of the
present invention;
[0042] FIG. 5 is a cross-sectional view illustrating the MR head of
the present invention along with a magnetic disk;
[0043] FIG. 6 is a cross-sectional view illustrating an MR head
integrated with a recording head according to the present
invention;
[0044] FIG. 7 is a cross-sectional view illustrating another MR
head of the present invention;
[0045] FIG. 8 is a flow chart illustrating steps of producing an MR
head of the present invention;
[0046] FIG. 9 is a flow chart illustrating steps of producing an MR
device section of the present invention;
[0047] FIG. 10 is a graph illustrating an MR device curve of the
present invention;
[0048] FIG. 11 is a graph illustrating the composition dependency
of an MR device ratio of the present invention in which a
Co.sub.1-xFe.sub.x alloy is employed as a first ferromagnetic
layer;
[0049] FIG. 12 is a graph illustrating an MR device curve of the
present invention;
[0050] FIG. 13 is a graph illustrating another MR device curve of
the present invention;
[0051] FIG. 14 is a graph illustrating the MR ratio, Hp, Hc and Hd
with respect to the thickness (t) of an .alpha.-Fe.sub.2O.sub.3
film in an MR device of the present invention; and
[0052] FIG. 15 shows graphs illustrating the MR ratio and Hp with
respect to the temperature of a heat treatment in an MR device of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] An MR device and an MR head of the present invention will
now be described with reference to the accompanying figures.
[0054] FIGS. 1A, 1B, 2A and 2B illustrate the MR device of the
present invention. The MR device of the present invention includes
an antiferromagnetic film 3, a first ferromagnetic film 4, a
non-magnetic film 5 and a second ferromagnetic film 6, deposited in
this order on a non-magnetic substrate 1. In the exemplary
structure illustrated in FIGS. 1A and 1B, the first ferromagnetic
film 4 (pin layer) is subject to an exchange bias magnetic field
from the antiferromagnetic film 3, and thus has one fixed
magnetization direction. In contrast, the magnetization direction
of the second ferromagnetic film 6 provided on the non-magnetic
film 5 changes relatively freely in response to an external
magnetic field. Thus, the magnetization direction of the second
ferromagnetic film (free layer) 6 and that of the first
ferromagnetic film (pin layer) 4 change with respect to each other,
thereby changing the electric resistance (magnetic resistance).
Based on the same principle, an MR sensor can read a resistance
change caused by the external magnetic field as an electric
signal.
[0055] Preferably, the antiferromagnetic film 3 is an oxide
antiferromagnetic film such as an NiO film, a CoO film or an
.alpha.-Fe.sub.2O.sub.3 film. The .alpha.-Fe.sub.2O.sub.3 film is
particularly preferred. It is known that, among the conventional
metallic antiferromagnetic materials, the MR ratio of the spin
valve film using NiO is greater than that of the spin valve film
using a metallic antiferromagnetic material such as Fe--Mn. This is
explained as follows. When the spin valve film using NiO is used, a
mirror reflection of conducted electrons occurs at the interface of
the antiferromagnetic film 3 and the first ferromagnetic film (pin
layer) 4 (Physical Review B, Vol. 53, p. 9108 (1996-II)). In order
for a mirror reflection to occur at the interface, the interface
between the antiferromagnetic film 3 and the first ferromagnetic
film (pin layer) 4 is smooth enough in view of the wavelength of
the conducted electrons (several angstroms). The present invention
makes it possible to improve the smoothness of the interface and
thereby obtain a larger MR ratio from an .alpha.-Fe.sub.2O.sub.3
spin valve film than has been conventionally been realized
(Japanese Laid-open Publication Nos. 8-279117 and 9-92904).
[0056] When evaluating the smoothness of the interface between an
antiferromagnetic film and a ferromagnetic film, it is preferable
to be able to directly evaluate the smoothness of the interface or
the surface of the antiferromagnetic film 3. Otherwise, it may also
be evaluated by measuring the smoothness of the surface of the
multilayer film. In such a case, although the surface should
preferably be completely smooth across the entire area, there may
be an undulation as high as several hundred angstroms, as long as
the surface includes a smooth area with an angstrom tolerance.
Preferably, about 10%, and more preferably about 20%, of the entire
area should be smooth with only undulations of about 0.5 nm or
less.
[0057] The exemplary structure illustrated in FIGS. 1A, 1B, 2A and
2B employs an .alpha.-Fe.sub.2O.sub.3 film 3. One advantage of an
oxide antiferromagnetic film over a metallic antiferromagnetic
film, such as an Fe--Mn film, an Ni--Mn film, a Pd--Mn film, a
Pt--Mn film, an Ir--Mn film or an Fe--Ir film, is that the oxide
antiferromagnetic film 3 generally has a larger MR ratio. Another
advantage thereof is that, when the MR device is used as an MR
head, the thickness of the entire MR device including the shield
gap material (corresponding to the shield gap distance d in FIG. 6)
can be small because the oxide antiferromagnetic film 3 is an
insulation film and thus can be considered as a part of the
underlying insulation film (shield gap). An MR head with a small
shield gap distance d is suitable for high density recording with a
very high recording density expected in the future.
[0058] As illustrated in FIG. 1A, when the .alpha.-Fe.sub.2O.sub.3
film 3 is used by itself, it should preferably have a thickness of
at least about 5 nm, but about 40 nm or less.
[0059] When the .alpha.-Fe.sub.2O.sub.3 film 3 is layered together
with another antiferromagnetic film (not shown) such as an NiO film
or a CoO film, it is possible to more effectively apply the
exchange bias magnetic field to the pin layer 4 than in the case
where the .alpha.-Fe.sub.2O.sub.3 film 3 is used by itself. With
the thickness being equal, a layered film provides advantages such
as a greater exchange bias magnetic field and a larger MR ratio.
With the MR characteristic being equal, a layered film is
advantageous because the total thickness of the device can be
smaller.
[0060] Where the .alpha.-Fe.sub.2O.sub.3 film 3 is layered on an
NiO film, a CoO film, or the like, a great exchange bias magnetic
field can be applied to the pin layer 4 (first ferromagnetic layer)
when the thickness of the .alpha.-Fe.sub.2O.sub.3 film 3 is in a
range between about 5 nm and about 40 nm, and more preferably in a
range between about 10 nm and about 40 nm. In such a case, the
thickness of the NiO or CoO film is preferably in a range between
about 5 nm and about 40 nm, and more preferably in a range between
about 10 nm and about 30 nm. The thickness of the
.alpha.-Fe.sub.2O.sub.3 film 3 should be equal to or greater than
that of the NiO or CoO film.
[0061] In the layered antiferromagnetic film, the NiO film
preferably overlies the .alpha.-Fe.sub.2O.sub.3 film 3. Although
such a layered antiferromagnetic film, as compared with one with
the .alpha.-Fe.sub.2O.sub.3 film 3 overlying the NiO film, has a
slightly lower MR ratio, it can provide a greater exchange bias
magnetic field, whereby the entire structure can be thinner. For
example, with a total thickness of about 20 nm, a sufficient
exchange bias magnetic field can be provided. In such a case, the
thickness of the .alpha.-Fe.sub.2O.sub.3 film is preferably in a
range between about 5 nm and about 30 nm, and the thickness of the
NiO film is preferably in a range between about 5 nm and about 20
nm.
[0062] It is also effective to use an indirect exchange coupling
film 50 as illustrated in FIG. 2A in order to further increase the
bias magnetic field applied to the pin layer 4 (or to further
stabilize the magnetization direction of the pin layer 4). The
indirect exchange coupling film 50 can be obtained by inserting an
appropriate non-magnetic film 52 between ferromagnetic films 51 and
53. For example, by providing an Ru film having a thickness of
about 0.7 nm as the non-magnetic film 52 and Co films as the
ferromagnetic films 51 and 53, a strong indirect exchange
interaction acts between the two ferromagnetic films 51 and 53,
thereby stabilizing the magnetization direction of the pin layer 4.
If the magnetization direction of the ferromagnetic film 53 is
further secured by the antiferromagnetic film 3, the magnetization
direction of the pin layer 4 is further stabilized.
[0063] In the structure illustrated in FIG. 2A, in addition to the
Co film, a Co--Fe film, an Ni--Fe--Co film, or the like, may
alternatively be used as the ferromagnetic films 51 and 53. The
thickness of the ferromagnetic films 51 and 53 should be at least
about 1 nm, and should preferably be about 4 nm or less.
Preferably, the respective thicknesses of the ferromagnetic films
51 and 53 are not identical to each other, but rather differ from
each other by at least about 0.5 nm. In addition to the Ru film, a
Cu film, an Ag film, or the like, may alternatively be used as the
non-magnetic film 52. Preferably, the thickness of the non-magnetic
film 52 is in a range between about 0.3 nm and about 1.2 nm.
[0064] Si, glass, sapphire, MgO, or the like, can be used as a
material of the substrate 1. In an MR head, an Al.sub.2O.sub.3--TiC
substrate is typically used.
[0065] When a Co.sub.1-xFe.sub.x alloy (0<x.ltoreq.0.5, where x
denotes an atomic composition ratio) is used for the first and
second ferromagnetic films 4 and 6, a large MR ratio can be
obtained. Since it is important for the second ferromagnetic film 6
to have a soft magnetic property, an Ni--Fe alloy, an Ni--Fe--Co
alloy, or the like, is typically used as a material thereof. As a
material of the first ferromagnetic film 4, a Co.sub.1-xFe.sub.x
alloy, or the like, is preferably used so as to maximize the MR
ratio. Especially when a Cu film is used as the non-magnetic film,
the Co.sub.1-xFe.sub.x alloy results in a substantial amount of
scattering occurring depending upon a spin, thereby increasing the
MR ratio. An Ni--Fe film, an Ni-rich Ni--Fe--Co film, or the like,
is preferably used as the film which is in contact with the
.alpha.-Fe.sub.2O.sub.3 film 3 and subject to an exchange bias
magnetic field therefrom. Therefore, it is preferable to provide
the first ferromagnetic film 4 in a layered structure including an
Ni--Fe film, an Ni--Fe--Co film, or the like, on the
.alpha.-Fe.sub.2O.sub.3 film 3 side, and a Co--Fe film, or the
like, on the non-magnetic film 5 side. When the total thickness of
the first ferromagnetic film 4 is excessively small, the MR ratio
is reduced. When the total thickness of the first ferromagnetic
film 4 is excessively large, on the other hand, the exchange bias
magnetic field is reduced. Therefore, the total thickness of the
first ferromagnetic film 4 is preferably in a range between about 2
nm and about 10 nm, and more preferably equal to or less than about
5 nm.
[0066] An Ni--Fe alloy, an Ni--Co--Fe alloy, or the like, is
preferably used as a material of the second ferromagnetic film 6.
Preferably, the atomic composition ratio of the
Ni.sub.xCo.sub.yFe.sub.z film may be:
0.6.ltoreq.x.ltoreq.0.9
0.ltoreq.y.ltoreq.0.4
0.ltoreq.z.ltoreq.0.3
[0067] (thereby obtaining an Ni-rich soft magnetic film); or
0.ltoreq.x.ltoreq.0.4
0.2.ltoreq.y.ltoreq.0.95
0.ltoreq.z.ltoreq.0.5
[0068] (thereby obtaining a Co-rich film).
[0069] A film having such a composition exhibits a low
magnetostriction (1.times.10.sup.-5) which is required for an MR
sensor or an MR head. An amorphous film such as a Co--Mn--B film, a
Co--Fe--B film, a Co--Nb--Zr film or a Co--Nb--B film may
alternatively be used as a material of the second ferromagnetic
film 6.
[0070] Preferably, the thickness of the second ferromagnetic film 6
is in a range between about 1 nm and about 10 nm. When the second
ferromagnetic film 6 is excessively thick, the MR ratio is reduced
due to a shunt effect. When the second ferromagnetic film 6 is
excessively thin, the soft magnetic property is reduced. More
preferably, the thickness is in a range between about 2 nm and
about 5 nm.
[0071] It is also effective to provide a Co--Fe alloy film as an
interface magnetic film (not shown) at the interface between the
second ferromagnetic film 6 and the non-magnetic film 5. When the
interface magnetic layer is excessively thick, the sensitivity of
the MR ratio to the magnetic field is reduced. Therefore, the
thickness of the interface magnetic layer is preferably about 2 nm
or less, and more preferably about 1 nm or less. In order for the
interface magnetic film to effectively function, the thickness
thereof should be at least about 0.4 nm.
[0072] While a Cu film, an Ag film, an Au film, a Ru film, or the
like, can be used as the non-magnetic film 5, the Cu film is
particularly preferred. Preferably, the thickness of the
non-magnetic film 5 is at least about 1.5 nm, and more preferably
at least about 1.8 nm, in order to sufficiently suppress the
interaction between the magnetic films 4 and 6. When the
non-magnetic film 5 is excessively thick, the MR ratio is reduced.
Therefore, the thickness is preferably about 10 nm or less, and
more preferably about 3 nm or less.
[0073] A Pt film, an Au film, or the like, may be preferably used
as an underlying layer 2 illustrated in FIG. 1B. When the
.alpha.-Fe.sub.2O.sub.3 film 3 is formed on the underlying layer 2,
the crystallinity of the .alpha.-Fe.sub.2O.sub.3 film 3 is
improved, and the exchange bias magnetic field applied to the first
ferromagnetic film 4 is increased, thereby improving the MR
characteristic. The underlying layer 2 has another advantage of
smoothing the film surface. Thus, the interface between the
antiferromagnetic film 3 and the first ferromagnetic film 4 is
smoothed, and a mirror reflection effect is obtained, thereby
increasing the MR ratio. The thickness of the underlying layer 2 is
preferably at least about 1 nm, and more preferably at least about
10 nm. When the underlying layer 2 is excessively thick, the
production yield is reduced. Therefore, the thickness of the
underlying layer 2 is preferably about 50 nm or less, and more
preferably about 20 nm or less.
[0074] While a so-called "single spin valve film" structure (where
there is only one pin layer 4) has been described above, the
present invention may also effectively used with a "dual spin valve
film" structure (where there are two pin layers). An exemplary
"dual spin valve film" structure is illustrated in FIG. 2B.
Referring to FIG. 2B, the dual spin valve film structure
additionally includes a third ferromagnetic film 7 and an
antiferromagnetic film 8 on a non-magnetic film 5A. In this
structure, the third ferromagnetic film 7 can be formed of the same
material as that of the first ferromagnetic film 4. However, the
antiferromagnetic film 8 is preferably not an oxide film such as an
.alpha.-Fe.sub.2O.sub.3 film or an NiO film. Instead, a metallic
film using one of the following materials is more preferably used
for the antiferromagnetic film 8: Fe--Mn, Ni--Mn, Pd--Mn, Pt--Mn,
Ir--Mn, Cr--Al, Cr--Mn--Pt, Fe--Mn--Rh, Pd--Pt--Mn, Ru--Rh--Mn,
Mn--Ru, Cr--Al, or the like. This is because, where an
antiferromagnetic film is provided as an overlying layer, the
exchange bias is more effective when the antiferromagnetic film is
a metallic antiferromagnetic film than an oxide film. Among the
above listed materials, Fe--Mn has been most typically used in a
conventional spin valve film. However, in view of corrosion
resistance, an Fe--Mn film is less preferred in the present
invention, and an Ir--Mn film is particularly preferred.
Preferably, the atomic composition ratio of an Ir.sub.zMn.sub.1-z
film may be:
0.1.ltoreq.z.ltoreq.0.5.
[0075] For example, the layers 1 to 8 may be formed by using a
sputtering method, or a sputtering method in combination with a
vapor deposition method. The sputtering includes a DC sputtering
method, an RF sputtering method, an ion beam sputtering method, and
the like, all of which may be suitably used for producing the MR
device of the present invention. The RF sputtering method is
particularly preferred for forming the .alpha.-Fe.sub.2O.sub.3 film
3 or the NiO film.
[0076] FIG. 4 illustrates an exemplary structure of an MR head of
the present invention incorporating the above-described MR device.
FIG. 3 illustrates the structure of the MR head as viewed from a
direction indicated by A in FIG. 4. FIG. 5 illustrates a
cross-sectional view taken along a plane indicated by B in FIG. 4.
In the following description, FIG. 3 is mostly referred to.
[0077] Referring to FIG. 3, an MR device section 9 is interposed
between upper and lower shield gaps 14 and 11. An insulation film
such as an Al.sub.2O.sub.3 film, an SiO.sub.2 film, or the like,
may be used as the shield gaps 11 and 14. Upper and lower shields
15 and 10 are further provided on the shield gaps 14 and 11,
respectively. A soft magnetic film such as an Ni--Fe alloy film may
be used as the shield material. In order to control the magnetic
domain of the MR device, a bias magnetic field is applied by a hard
bias section 12 made of a material such as a Co--Pt alloy. While a
hard film is used in this instance for applying a bias magnetic
field, an antiferromagnetic film such as an Fe--Mn film can be used
similarly. The MR device section 9 is insulated from the shields 10
and 15 by the shield gaps 11 and 14, and changes in the resistance
of the MR device section 9 can be read by applying an electric
current thereto through a lead section 13.
[0078] Since an MR head is a read only head, it is typically used
in combination with an induction head for writing. FIGS. 5 and 6
illustrate a write head section 31 as well as a read head section
32. FIG. 6 illustrates the same structure as illustrated in FIG. 3
with the write head section 31 being additionally provided thereon.
The write head section 31 includes an upper core 16 which is
provided above the upper shield 15 via a recording gap film 40.
[0079] While FIG. 6 illustrates an MR head having a conventional
abutted junction, FIG. 7 illustrates another effective MR head with
an overlaid structure in which a track width 41 can be more
precisely controlled. Therefore, the structure illustrated in FIG.
7 may be able to better account for a track width reduction
resulting from an increase in the recording density.
[0080] Now, the recording and reproduction mechanism of the MR head
will be described with reference to FIG. 5. Referring to FIG. 5,
during a recording operation, a magnetic flux which is generated by
an electric current and conducted through a coil 17 leaks through a
space between the upper core 16 and the upper shield 15, thereby
writing information on a magnetic disk 21. The head 30 moves in a
direction indicated by an arrow c in the figure with respect to the
magnetic disk 21, where it is possible to reverse a recording
magnetization direction 23 by reversing the direction of the
current flow though the coil 17. When the recording density is
increased, the recording length (recording pitch) 22 becomes
shorter, whereby it is necessary to reduce a recording gap length
(recording gap pitch) 19 accordingly.
[0081] In a reproduction operation, a magnetic flux 24 leaking from
a recording magnetization section of the magnetic disk 21 acts upon
the MR device section 9 between the shields 10 and 15, thereby
altering the resistance of the MR device. Since a current is
conducted to the MR device section 9 through the lead section 13, a
change in the resistance thereof can be read as a change in the
voltage (output) thereof.
[0082] Referring to FIG. 8, a method for producing the MR head will
now be described.
[0083] First, the lower shield 10, as illustrated in FIG. 3, is
formed on an appropriately processed substrate (S801). Then, the
lower gap shield 11 is formed on the lower shield 10 (S802), and an
MR device section layer is formed on the lower shield gap 11
(S803). After the MR device section layer is patterned into the MR
device section 9, as illustrated in FIG. 3 (S804), the hard bias
section 12 (S805) and the lead section 13 (S806) are formed. Then,
the upper shield gap 14 (S807) and the upper shield 15 (S808) are
formed. Finally, the write head section 31 is formed, as
illustrated in FIG. 6 (S809), thereby obtaining an MR head.
[0084] Referring to FIG. 9, the step of forming the MR device
section 9 (S803) will be described in greater detail. The
antiferromagnetic film 3 is formed by sputtering a target of
.alpha.-Fe.sub.2O.sub.3 onto the non-magnetic substrate 1, as
illustrated in FIG. 1A (S901). Then, the first ferromagnetic film
4, the non-magnetic film 5 and the second ferromagnetic film 6 are
deposited in this order on the antiferromagnetic film 3, thereby
obtaining the MR device section 9 (S902).
[0085] In order to obtain the MR device as illustrated in FIG. 2B,
the non-magnetic film 5A, the third ferromagnetic film 7 and the
antiferromagnetic film 8 are deposited in this order on the second
ferromagnetic film 6, thereby obtaining the MR device section.
[0086] In view of a future increase in a recording density of a
hard disk drive, the recording wavelength (recording pitch) should
be shortened, for which it is necessary to shorten the distance d
(indicated by reference numeral 18 in FIG. 5) between the shields
as illustrated in FIG. 3. As can be seen from FIG. 3, it is
necessary to reduce the thickness of the MR device section 9.
Preferably, the thickness of the MR device section 9, excluding the
antiferromagnetic film, should be about 20 mm or less. The
antiferromagnetic .alpha.-Fe.sub.2O.sub.3 film used the present
invention is an insulation film. Therefore, if the
antiferromagnetic .alpha.-Fe.sub.2O.sub.3 film is provided as a
part of the insulation film (e.g., as a part of the gap shield 11
in FIG. 3), the thickness thereof is less restricted. When the
antiferromagnetic .alpha.-Fe.sub.2O.sub.3 film is provided as a
part of the MR device section 9, however, it should be as thin as
possible. Preferably, the thickness of the antiferromagnetic
.alpha.-Fe.sub.2O.sub.3 film should be about 40 nm or less, and
more preferably about 20 nm or less.
[0087] In the MR device section, an axis of easy magnetization
(also referred to as an "easy axis") of the second ferromagnetic
film (free layer) 6, as illustrated in FIGS. 1A, 1B, 2A and 2B is
preferably arranged to be substantially perpendicular to the
direction of a magnetic field of a signal to be detected, in order
to suppress generation of Barkhausen noise during magnetization
switching of the soft magnetic film.
[0088] The MR device and the MR head of the present invention will
now be described by way of illustrative examples.
EXAMPLE 1
[0089] In Example 1, the MR devices each having the structure as
illustrated in FIG. 1A on a glass substrate were produced using a
sputtering apparatus having .alpha.-Fe.sub.2O.sub.3, Co,
Co.sub.0.85Fe.sub.0.15, Ni.sub.0.68Fe.sub.0.20Co.sub.0.12, Cu and
Fe.sub.0.5Mn.sub.0.5 as targets. After a vacuum chamber was
exhausted to about 1.times.10.sup.-8 Torr, an Ar gas was supplied
therein so as to maintain the pressure therein at about 0.8 mTorr
while the structure was formed on the substrate using a sputtering
method. A Co.sub.0.85Fe.sub.0.15 alloy was used for the first
ferromagnetic film 4, and Cu was used for the non-magnetic film 5.
A layered structure including Co.sub.0.85Fe.sub.0.15 and
Ni.sub.0.68Fe.sub.0.20Co.sub.0.12 was employed for the second
ferromagnetic film 6. Another Cu layer was formed on the second
ferromagnetic film 6 as a protective layer.
[0090] Four different sample devices A1-A4 were produced. The
respective materials and thicknesses used to form the layers for
each of the samples A1-A4 are shown below (thickness in nm shown in
parentheses). The sample device A3 produced with an Fe--Mn
antiferromagnetic film is a comparative device which employs a
conventional Fe--Mn alloy. Since the antiferromagnetic film 3 has
to be formed after the pin layer 4 is formed, the free layer was
formed first (opposite order from that when the
.alpha.-Fe.sub.2O.sub.3 is employed). An RF cathode was used when
the .alpha.-Fe.sub.2O.sub.3 was employed, and a DC cathode was used
when any other material was employed.
[0091] A1:
.alpha.-Fe.sub.2O.sub.3(50)/Co.sub.0.86Fe.sub.0.15(2)/Cu(2)/Co.-
sub.0.45Fe.sub.0.15(1)/Ni.sub.0.68Fe.sub.0.20Co.sub.0.12(2)/Cu(0.4)
[0092] A2:
.alpha.-Fe.sub.2O.sub.3(50)/Co(2)/Cu(2)/Co(1)/Ni.sub.0.68Fe.sub-
.0.20Co.sub.0.12(2)/Cu(0.4)
[0093] A3:
Ni.sub.0.88Fe.sub.0.20Co.sub.0.12(2)/Co.sub.0.85Fe.sub.0.15(1)/-
Cu(2)/Co.sub.0.85Fe.sub.0.15(2)Fe.sub.0.5Mn.sub.0.5(10)/Cu(0.4)
[0094] A4:
.alpha.-Fe.sub.2O.sub.3(50)/Ni.sub.0.8Fe.sub.0.20(1)Co.sub.0.85-
Fe.sub.0.15(1)/Cu(2)
Co.sub.0.85Fe.sub.0.15(1)/Ni.sub.0.68Fe.sub.0.20Co.su-
b.0.12(2)/Cu(0.4)
[0095] The composition of each produced film was close to the
original composition of the target material. For example, while
.alpha.-Fe.sub.2O.sub.3 has the inherent composition of Fe/O=1/1.5,
an analysis showed that a produced .alpha.-Fe.sub.2O.sub.3 film had
a composition of Fe/O=1/1.45.
[0096] The composition ratio does not have to be exactly 1/1.5.
When .alpha.-Fe.sub.2O.sub.3 was employed as a target, excellent MR
characteristics were obtained even when the production condition
such as a sputtering pressure was somewhat varied. Thus, the
present invention can be effective as long as the composition Fe/O
is in a range from about 1/1.35 to about 1/1.55.
[0097] Characteristics of a produced MR device (sample A1) were
evaluated while applying a magnetic field of up to about 40 kA/m
(500 Oe) by a DC 4-terminal method at room temperature.
[0098] An MR curve 91 obtained for the sample A1 is shown in FIG.
10. In FIG. 10, the horizontal axis represents an applied magnetic
field and the vertical axis represents the MR ratio, which is a
rate of change (%) in resistance with the resistance measured at an
applied magnetic field of 40 kA/m being a reference. FIG. 10
generally illustrates the respective magnetization directions of
the pin layer (first ferromagnetic layer 4) and the free layer
(second ferromagnetic layer 6) at the points (a), (b) and (c) along
the MR curve 91. FIG. 10 shows that the MR device of the present
invention exhibits a very large MR ratio.
[0099] When a magnetic field of about -40 kA/m is applied, the pin
layer 4 and the free layer 6 have substantially the same direction
(point (a)). As the magnetic field is increased gradually and over
the value "0", the magnetization direction of the second
ferromagnetic film 6 (free layer) is reversed, and then the MR
ratio rapidly increases toward point (b). When the applied positive
magnetic field is further increased, the magnetization direction of
the pin layer 4 is also reversed, thereby reducing the MR ratio
toward point (c). Referring to FIG. 10, an exchange bias magnetic
field "Hp" is defined as a magnitude of magnetic field being
applied when the MR ratio becomes half of its peak after passing
the peak (point (b)). This value Hp is used for evaluating the
exchange bias magnetic field of the .alpha.-Fe.sub.2O.sub.3 film.
Typically, a greater exchange bias magnetic field indicates a more
stable magnetization direction of the pin layer 4 (and thus more
suitable for an MR device). Table 1 below shows the MR ratios and
the Hp values of the samples A1-A4 measured as described above.
1TABLE 1 Sample MR ratio (%) Hp (kA/m) A1 16.5 13 A2 10.2 15 A3 5.2
18 A4 15.8 25
[0100] Table 1 shows the following. The sample MR device A1 which
employs .alpha.-Fe.sub.2O.sub.3 exhibits a greater
magnetoresistance change than that of the sample device A3 which
employs the conventional Fe--Mn alloy. Each of the MR devices A1,
A2, A4 using a Co--Fe alloy exhibits a larger MR ratio than that of
the MR device A3 using Co. In the sample device A4 whose first
magnetic layer is provided with a double-layered structure
including an Ni--Fe layer and a Co--Fe layer, the exchange bias
magnetic field is considerably large (nearly doubled from that of
A1), while the MR ratio thereof is not considerably changed. It can
be seen that the sample device A4 is more stable to the external
magnetic field.
[0101] Another sample device A5 was produced employing materials
and thicknesses as shown below, and the MR characteristics thereof
were evaluated so as to determine the composition dependency of the
Co.sub.1-xFe.sub.x (pin) layer (x: atomic composition ratio).
[0102] A 5:
.alpha.-Fe.sub.2O.sub.3(60)/Co.sub.1-xFe.sub.x(2)/Cu(3)/Co.sub-
.0.85Fe.sub.0.15(5)/Cu(0.4)
[0103] FIG. 11 shows the composition dependency of the MR ratio of
the sample device A5. It can be seen that the MR ratio varies
substantially depending upon the composition ratio of
Co.sub.1-xFe.sub.x. In a range of 0<x.ltoreq.0.5, the MR ratio
shows a rapid increase.
[0104] Next, MR heads as illustrated in FIG. 3 were produced
respectively using the sample devices A1 (the present invention),
A2 and A3 (comparative examples), and the characteristics thereof
were evaluated. In each of the produced MR heads, an
Al.sub.2O.sub.3--TiC material was employed for the substrate, an
Ni.sub.0.8Fe.sub.0.2 alloy for the shields 10 and 15, and
Al.sub.2O.sub.3 for the shield gaps 11 and 14. Moreover, a Co--Pt
alloy was used for the hard bias section 12, and Au for the lead
section 13. The magnetic films were provided with an anisotropy in
such a way that the easy axis of the pin layer (first ferromagnetic
film 4) was substantially parallel to the direction of a magnetic
field of a signal to be detected, whereby the easy axis of the free
layer (second ferromagnetic film 6) was substantially perpendicular
to the direction of the magnetic field of the signal to be
detected. The magnetic films were deposited while using a permanent
magnet so as to apply the films with a magnetic field in a desired
direction of anisotropy in the film plane. The respective outputs
of the produced heads were evaluated while applying an alternating
signal magnetic field of about 50 Oe to the heads. The output of
the MR head employing the MR device A1 of the present invention was
about 50% and about 100% higher than those of the MR heads
employing the comparative MR devices A2 and A3, respectively.
Example 2
[0105] The following sample MR devices B1-B3 each having the
structure as that illustrated in FIG. 1B were produced in the same
manner as that of Example 1.
[0106] B1:
Pt(10)/.alpha.-Fe.sub.2O.sub.3(40)/Co.sub.0.85Fe.sub.0.15(2)/Cu-
(2.1)/Co.sub.0.85Fe.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(0.4)
[0107] B2:
Au(10)/.alpha.-Fe.sub.2O.sub.3(40)/Co.sub.0.85Fe.sub.0.15(2)/Cu-
(2.1)/Co.sub.0.85Fe.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(0.4)
[0108] B3:
.alpha.-Fe.sub.2O.sub.3(40)/Co.sub.0.85Fe.sub.0.15(2)/Cu(2.1)/C-
o.sub.0.85Fe.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(0.4)
[0109] The produced sample devices B1-B3 were subjected to the same
evaluation as that of Example 1. The results are shown in Table 2
below.
2TABLE 2 Sample MR ratio (%) Hp (kA/m) B1 15.1 37 B2 12.2 29 B3
10.6 9
[0110] Table 2 shows the following. By employing the Pt or Au
underlying layer (B1, B2), it is possible to obtain a great
exchange bias magnetic field Hp even when the
.alpha.-Fe.sub.2O.sub.3 layer is relatively thin. With no
underlying layer and a relatively thin .alpha.-Fe.sub.2O.sub.3
layer (B3), the exchange bias magnetic field is not efficiently
effected and becomes weak. In such a case, the magnetization
antiparallelism between the pin layer 4 and the free layer 6 is not
completely achieved, thereby reducing the MR ratio.
Example 3
[0111] The following sample MR devices C1-C12 each having the
structure as that illustrated in FIG. 1A were produced in the same
manner as that of Example 1, while employing a layered oxide
structure as the antiferromagnetic layer. An RF cathode was used
when an NiO or CoO film was employed.
[0112] C1:
NiO(10)/.alpha.-Fe.sub.2O.sub.3(30)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0113] C2:
NiO(10)/.alpha.-Fe.sub.2O.sub.3(20)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0114] C3:
NiO(10)/.alpha.-Fe.sub.2O.sub.3(10)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0115] C4:
CoO(10)/.alpha.-Fe.sub.2O.sub.3(30)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0116] C5:
.alpha.-Fe.sub.2O.sub.3(30)/Co(2)/Cu(2.5)/Co.sub.0.85Fe.sub.0.1-
5(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2) ps
[0117] C6:
.alpha.-Fe.sub.2O.sub.3(40)/NiO(10)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0118] C7:
.alpha.-Fe.sub.2O.sub.3(30)/NiO(10)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0119] C8:
.alpha.-Fe.sub.2O.sub.3(20)/NiO(10)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0120] C9:
.alpha.-Fe.sub.2O.sub.3(10)/NiO(10)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0121] C10:
NiO(40)/Co(2)/Cu(2.5)/Co.sub.0.85Fe.sub.0.15(1)/Ni.sub.0.8Fe.s-
ub.0.20(5)/Cu(2)
[0122] C11:
NiO(10)/.alpha.-Fe.sub.2O.sub.3(8)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0123] C12:
.alpha.-Fe.sub.2O.sub.3(40)/NiO(4)/Co(2)/Cu(2.5)/Co.sub.0.85Fe-
.sub.0.15(1)/Ni.sub.0.8Fe.sub.0.20(5)/Cu(2)
[0124] The produced sample devices C1-C12 were subjected to the
same evaluation as that of Example 1. The results are shown in
Table 3 below.
3TABLE 3 Sample MR ratio (%) Hp (kA/m) C1 12.1 20 C2 12.3 18 C3
12.1 15 C4 9.9 10 C5 1.8 7 C6 11.2 More than 40 C7 11.5 39 C8 11.1
35 C9 11.3 20 C10 9.4 9 C11 6.7 11 C12 3.1 8
[0125] As is apparent from Table 3, each of the MR devices C1-C4
and C6-C9 of the present invention which employ a layered oxide
antiferromagnetic structure exhibit a larger MR ratio than that of
the MR device C5 which employs the conventional single layer
antiferromagnetic structure. It is believed that the reason for
this is as follows. In the sample device C5, the exchange bias
magnetic field to the first ferromagnetic layer is weak, whereby
sufficient magnetization antiparallelism is not realized, thereby
reducing the MR ratio. When a layered antiferromagnetic structure
is provided, on the other hand, a sufficient exchange bias magnetic
field is applied to the ferromagnetic layer, whereby sufficient
magnetization antiparallelism is realized.
[0126] A comparison between the sample devices C1-C3 and sample
devices C6-C9 shows the following. Each of the sample devices C1-C3
where the NiO layer is formed before forming the
.alpha.-Fe.sub.2O.sub.3 layer tends to have a larger MR ratio and a
slightly lower Hp value. On the other hand, each of the sample
devices C6-C9 where the .alpha.-Fe.sub.2O.sub.3 layer is formed
before forming the NiO layer tends to have a slightly lower MR
ratio and a greater Hp value. Each of the sample devices C6-C9
which employs the .alpha.-Fe.sub.2O.sub.3/NiO layered
antiferromagnetic structure exhibits a larger MR ratio and a
greater exchange bias magnetic field Hp than those of the sample
device C10 which employs the NiO single layer antiferromagnetic
structure.
[0127] Moreover, comparison between the sample devices C1-C3 of the
present example and the sample device C11 of the comparative
example shows that, when depositing the NiO film before depositing
the .alpha.-Fe.sub.2O.sub.3 film, it is preferable to provide the
.alpha.-Fe.sub.2O.sub.3 film with a thickness substantially equal
to or greater than that of the NiO film.
[0128] Furthermore, comparison between the sample device C6 and the
sample device C12 shows that, when depositing the
.alpha.-Fe.sub.2O.sub.3 film before depositing the NiO film, it is
preferable to provide the NiO film with a thickness of at least
about 5 nm.
Example 4
[0129] The following sample MR devices D1-D6 each having the
structure as that illustrated in FIG. 2 were produced in the same
manner as that of Example 1.
[0130] D1:
.alpha.-Fe.sub.2O.sub.3(60)/Co.sub.0.85Fe.sub.0.15(2)/Cu(2)/Co.-
sub.0.85Fe.sub.0.15(0.4)/Ni.sub.0.68Fe.sub.0.20Co.sub.0.12(5)/Co.sub.0.85F-
e.sub.0.15(0.4)/Cu(2)/Co.sub.0.85Fe.sub.0.15(2)Ir.sub.0.2Mn.sub.0.8(8)
[0131] D2:
NiO(10)/.alpha.-Fe.sub.2O.sub.3(30)/Co.sub.0.85Fe.sub.0.15(2)/C-
u(2)/Co.sub.0.85Fe.sub.0.15(0.4)/Ni.sub.0.68Fe.sub.0.20Co.sub.0.12(5)/Co.s-
ub.0.85Fe.sub.0.15(0.4)/Cu(2)/Co.sub.0.85Fe.sub.0.15(2)/Ir.sub.0.2Mn.sub.0-
.8(8)
[0132] D3:
.alpha.-Fe.sub.2O.sub.3(20)/NiO(10)/Co.sub.0.85Fe.sub.0.15(2)/C-
u(2)/Co.sub.0.85Fe.sub.0.15(0.4)/Ni.sub.0.68Fe.sub.0.20Co.sub.0.12(5)/Co.s-
ub.0.85Fe.sub.0.15(0.4)/Cu(2)/Co.sub.0.85Fe.sub.0.15(2)/Ir.sub.0.2Mn.sub.0-
.8(8)
[0133] D4:
.alpha.-Fe.sub.2O.sub.3(60)/Co.sub.0.85Fe.sub.0.15(2)/Cu(2)/Co.-
sub.0.85Fe.sub.0.15(0.4)/Ni.sub.0.68Fe.sub.0.20Co.sub.0.12(5)/Co.sub.0.85F-
e.sub.0.15(0.4)/ Cu(2)/Co.sub.0.85Fe.sub.0.15(2)/FeMn(8)
[0134] D5:
.alpha.-Fe.sub.2O.sub.3(60)/Co.sub.0.85Fe.sub.0.15(2)/Cu(2)/Co.-
sub.0.85Fe.sub.0.15(0.4)/Ni.sub.0.68Fe.sub.0.20Co.sub.0.12(5)/Co.sub.0.85F-
e.sub.0.15(0.4)/Cu(2)/Co.sub.0.85Fe.sub.0.15(2)/.alpha.-Fe.sub.2O.sub.3(60-
)
[0135] D6:
Ir.sub.0.2Mn.sub.0.8(8)/Co.sub.0.85Fe.sub.0.15(2)/Cu(2)/Co.sub.-
0.85Fe.sub.0.15(0.4)/Ni.sub.0.68Fe.sub.0.20Co.sub.0.12(5)/Co.sub.0.85Fe.su-
b.0.15(0.4)/Cu(2)/Co.sub.0.85Fe.sub.0.15(2)/Ir.sub.0.2Mn.sub.0.8(8)
[0136] FIG. 12 shows the MR curve of the sample device D1 as
measured in the same manner as that of Example 1. It can be seen
that the sample device D1 has a very high MR ratio and a sufficient
bias magnetic field. The measured MR ratios of the respective
sample devices D1-D6 are shown in Table 4 below.
4 TABLE 4 Sample MR ratio (%) D1 24.3 D2 25.1 D3 21.5 D4 14.2 D5
20.5 D6 7.8
[0137] As shown in Table 4, although the MR ratio of each of the
sample devices D2 and D3 of the present example is about the same
as that of the sample device D1, that MR ratio can be realized with
a smaller thickness due to the layered antiferromagnetic structure.
The MR ratio of each of the sample devices D2 and D3 of the present
example is greater than those of the comparative sample devices
D4-D6. It can also be seen that the sample device D4 (which employs
an Fe--Mn material for the second antiferromagnetic film) and the
sample device D6 (which employs an Ir--Mn material for both of the
first and second antiferromagnetic films) each have a low MR ratio.
The sample device D5 (which employs an .alpha.-Fe.sub.2O.sub.3
material for both of the first and second antiferromagnetic films)
has a large MR ratio, but the exchange bias magnetic field Hp is
only about half of that of the sample device D1. This is because
the .alpha.-Fe.sub.2O.sub.3 film employed as the antiferromagnetic
film has only a weak pinning effect. Thus, a metallic
antiferromagnetic film such as an Ir--Mn film is preferred as the
second antiferromagnetic film.
Example 5
[0138] In this example, a plurality of sample devices E were
produced with various surface roughnesses by previously processing
the surfaces of the glass substrates with an ion beam under various
conditions. The sample devices were produced in the same manner as
that of Example 1.
[0139] E:
Au(20)/.alpha.-Fe.sub.2O.sub.3(20)/Co.sub.0.85Fe.sub.0.15(2)/Cu(-
2)/Ni.sub.0.68Fe.sub.0.20CO.sub.0.12(3)
[0140] Table 5 below shows the respective surface roughnesses and
the MR ratios of the produced sample devices. The surface roughness
was evaluated by using an STM (Scanning Tunneling Microscope). Ten
10 nm.times.10 nm areas were randomly selected across the 10
mm.times.10 mm surface of each sample device. The surface roughness
of each area was determined as the difference in height between the
highest point therein and the lowest point therein. The surface
roughness values of the ten areas were averaged to obtain the
surface roughness of that sample device.
5 TABLE 5 Surface roughness (nm) MR ratio (%) 0.38 13.3 0.45 12.9
0.52 8.6 0.68 4.3 1.22 2.7
[0141] Table 5 shows that when the surface roughness is about 0.5
nm or less, the device exhibits a large MR ratio.
Example 6
[0142] A sample device F was produced as follows. An Si substrate
was used as the substrate, and a substrate preparation process
chamber was exhausted to about 2.times.10.sup.-6 Torr or less,
after which an Ar gas was introduced into the preparation chamber
until the pressure therein was about 4.5.times.10.sup.-4 Torr.
Then, the substrate surface was cleaned for about 20 minutes using
an ECR ion source with an acceleration voltage of about 100 V.
Thereafter, the resulting substrate was transferred into a
deposition chamber which was in communication with the preparation
chamber, and the sample device F was produced in the same manner as
that of Example 1.
[0143] F:
.alpha.-Fe.sub.2O.sub.3(t)/Co(2)/Cu(2)/Co.sub.0.90Fe.sub.0.10(1)-
/Ni.sub.0.8Fe.sub.0.20(5)/Ta(3)
[0144] FIG. 13 shows an MR curve for the sample device F where the
thickness of the .alpha.-Fe.sub.2O.sub.3 film (t) was t=10. The MR
curve was measured while applying a weak magnetic field of about 6
kA/m, where it is possible to observe changes in the MR ratio
solely due to the reversing magnetization direction of the free
layer 6 while the magnetization direction of the pin layer 4 is
fixed. In FIG. 13, "Hc" denotes a value which corresponds to the
coercive force of the magnetization curve, and "Hd" denotes a shift
between the center of the MR curve and the zero magnetic field.
Regarding the operation of the MR device, the MR curve shows that
as the values Hc and Hd are smaller, the resistance change near the
zero magnetic field is greater, indicating that the MR device is a
desirable device with a high sensitivity.
[0145] FIG. 14 shows the MR ratio, Hp, Hd and Hc of the sample
device F with respect to the thickness of the
.alpha.-Fe.sub.2O.sub.3 film (t). Referring to FIG. 14, the MR
ratio does not considerably change as the thickness of the
.alpha.-Fe.sub.2O.sub.3 film (t) is varied in this range. The value
Hp increases as the thickness of the .alpha.-Fe.sub.2O.sub.3 film
(t) increases. Although this may present a problem when the
.alpha.-Fe.sub.2O.sub.3 layer is thin, the value Hp can be
maintained at about 40 kA/m or greater by processing the sample
device at about 300.degree. C. in a magnetic field of about 40 kA/m
(this can be appreciated also from the following Example 7). Thus,
Hp does not present a critical problem. The value Hc or Hd
decreases as the thickness of the .alpha.-Fe.sub.2O.sub.3 film (t)
decreases.
[0146] Thus, it can be seen from FIG. 14 that the MR device of the
present invention (where the thickness of the
.alpha.-Fe.sub.2O.sub.3 film (t) is in a range between about 10 nm
and about 40 nm) is most suitable for use as a high sensitive MR
device, with a higher magnetic field sensitivity than that of the
conventional device (where the thickness of the
.alpha.-Fe.sub.2O.sub.3 film (t) is about 50 nm or greater).
Example 7
[0147] A sample MR device G was produced on a glass substrate in
the same manner as that of Example 1.
[0148] G: .alpha.-Fe.sub.2O.sub.3(t)/Co(2)/Cu(2)/Co(5)/Cu(0.4)
[0149] The sample device G was subjected to a heat treatment for
about 30 minutes in a vacuum of about 10.sup.-5 Torr or less while
applying thereto a magnetic field of about 40 kA/m.
[0150] FIG. 15 shows the MR ratio and the value Hp obtained from an
MR curve which was measured after the heat treatment. After a heat
treatment at 300.degree. C., the MR ratio of one sample device G
(where the thickness of the .alpha.-Fe.sub.2O.sub.3 film (t) is
about 50 nm) is reduced by about 30% of the MR ratio before the
heat treatment (at about 25.degree. C. in FIG. 15), while the MR
ratio of another sample device G (where the thickness of the
.alpha.-Fe.sub.2O.sub.3 film (t) is about 30 nm) is reduced only by
about 10% of the MR ratio before the heat treatment. When the
thickness of the .alpha.-Fe.sub.2O.sub.3 film (t) is about 10 nm,
the MR ratio is relatively low before the heat treatment, but it
increases as the device undergoes the heat treatment. After the
heat treatment at about 300.degree. C., the sample device G where
(t)=about 10 nm and the sample device G where (t)=about 30 nm have
larger MR ratios, and thus greater heat stabilities.
[0151] In the above description, the heat treatment was conducted
for about 30 minutes. In order to produce an actual MR head,
however, a longer heat treatment is required. After a 3 hour heat
treatment was conducted, the MR ratio of the sample device G where
(t)=about 50 nm was reduced by about 70%, while the MR ratio of the
sample device G where (t)=about 10 nm and the MR ratio of the
sample device G where (t)=about 30 nm were reduced only by about
20% or less. Thus, in view of the heat stability of the MR ratio of
the MR device, the thickness of the .alpha.-Fe.sub.2O.sub.3 film in
a range between about 10 nm and about 40 nm is preferable.
[0152] In FIG. 15, since the MR ratio is measured with a magnetic
field of about 40 kA/m, the value Hp of about 40 kA/m in FIG. 15
indicates that the value Hp is actually equal to or higher than 40
kA/m. As shown in FIG. 15, the value Hp exceeds about 40 kA/m after
a heat treatment at about 300.degree. C. Therefore, it is indicated
that a practically sufficient Hp value can be obtained after
subjecting the sample device G to a heat treatment at about
300.degree. C.
Example 8
[0153] The following sample MR devices H1-H3 were produced in the
same manner as that of Example 6. The sample device H2 has an
indirect exchange coupling film as illustrated in FIG. 2A.
[0154] H1:
.alpha.-Fe.sub.2O.sub.3(20)/Co(2)/Cu(2)/Co.sub.0.90Fe.sub.0.10(-
1)/Ni.sub.0.6Fe.sub.0.20(5)/Ta(5)
[0155] H2:
.alpha.-Fe.sub.2O.sub.3(20)/Co(1)/Ru(0.7)/Co(2)/Cu(2)/Co.sub.0.-
90Fe.sub.0.10(1)/Ni.sub.0.8Fe.sub.0.20(5)/Ta(5)
[0156] H3:
NiO(20)/Co(1)/Ru(0.7)/Co(2)/Cu(2)/Co.sub.0.90Fe.sub.0.10(1)/Ni.-
sub.0.8Fe.sub.0.20(5)/Ta(5)
[0157] The MR changes of the produced sample devices H1-H3 were
evaluated in the same manner as that of Example 1. The results are
shown in Table 6 below.
6TABLE 6 Sample MR ratio (%) Hp (kA/m) H1 12.5 9.2 H2 8.4 105 H3
8.2 108
[0158] As illustrated above, the sample device H2 of the present
example, as compared with the sample device H1 which does not have
the indirect exchange coupling film, has a reduced MR ratio but a
greater bias magnetic field Hp. Thus, it can be seen that the
sample device H2 is an MR device with a stable operation.
[0159] The comparative sample device H3 employs NiO as a material
for the antiferromagnetic film. The sample device H3 exhibited
characteristics substantially the same as those of the sample
device Hi at room temperature. At about 200.degree. C., however,
the sample device H3 exhibited considerably poor characteristics
with an MR ratio of about 2.2% and a value Hp of about 5 kA/m,
while the sample device H2 exhibited an MR ratio of about 7.1% and
a value Hp of about 52 kA/m.
[0160] Although Co is employed for the magnetic layers 51 and 53
which is used in the indirect exchange coupling film 50 in the
above examples, a Co--Fe alloy, a Co--Ni--Fe alloy, or the like,
can alternatively be used in place of Co. In such a case, the
thickness of each magnetic film should preferably be in a range
between about 1 nm and about 4 nm. Moreover, the respective
thicknesses of the ferromagnetic films 51 and 53 should differ from
each other by at least about 0.5 nm.
[0161] While Cu, Ru, Ag, or the like, can be used as the
non-magnetic film 52 in the indirect exchange coupling film 50, Ru
is most preferred. The thickness of the non-magnetic film 52 should
preferably be in a range between about 0.3 nm and about 1.2 nm.
[0162] Moreover, when one of the ferromagnetic films 4 and 7 is an
indirect exchange coupling film in the structure as illustrated in
FIG. 2B, a greater bias magnetic field can be obtained. The
following sample films H4 and H5 were produced each having
basically the same structure as that illustrated in FIG. 2B.
[0163] H4:
.alpha.-Fe.sub.2O.sub.3(20)/Co(2)/Cu(2)/Co.sub.0.90Fe.sub.0.10(-
1)/Ni.sub.0.8Fe.sub.0.20(5)/Co.sub.0.90Fe.sub.0.10(1)/Cu(2)/Co(2)/Pt.sub.0-
.50Mn.sub.0.50(25)/Ta(6)
[0164] H5:
.alpha.-Fe.sub.2O.sub.3(20)/Co(2)/Ru(0.7)/Co(3)/Cu(2)/Co.sub.0.-
90Fe.sub.0.10(1)/Ni.sub.0.8Fe.sub.0.20(5)/Co.sub.0.90Fe.sub.0.10(1)/Cu(2)/-
Co(2)/Pt.sub.0.50Mn.sub.0.50(25)/Ta(5)
7TABLE 7 Sample MR ratio (%) Hp (kA/m) H4 22.3 18 H5 19.5 75
[0165] As shown in Table 7, when the indirect exchange coupling
film (Co/Ru/Co film) is used, it is possible to produce a film
having a large Hp, though the MR ratio is smaller than when using a
single Co layer.
[0166] In this example, the indirect exchange coupling film is used
for the ferromagnetic film 4 in the structure of FIG. 2B.
Alternatively, the indirect exchange coupling film may be used for
the ferromagnetic film 7, or the indirect exchange coupling film
may be used for both of the ferromagnetic films 4.
[0167] As described above, according to the present invention, an
.alpha.-Fe.sub.2O.sub.3 film or an .alpha.-Fe.sub.2O.sub.3/NiO
layered film is used to precisely control the surface roughness of
the interface, whereby it is possible to realize an MR device which
exhibits a large MR ratio.
[0168] Various other modifications will be apparent to and can be
readily made by those skilled in the art without departing from the
scope and spirit of this invention. Accordingly, it is not intended
that the scope of the claims appended hereto be limited to the
description as set forth herein, but rather that the claims be
broadly construed.
* * * * *