Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-04-11
2002-05-14
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S900000, C360S112000, C360S125020, C360S125330, C338S03200R, C324S252000
Reexamination Certificate
active
06387550
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetoresistive material films for a giant magnetoresistive device employed in-magnetic heads, position sensors, rotation sensors and the like.
2. Description of the Related Art
An NiFe alloy (Permalloy) is a known magnetoresistive (MR) material which has been used for forming thin films for MR devices. Generally, the percentage change in resistance of a Permalloy thin film is within the range of 2 to 3%. Accordingly, magnetoresistive materials having magnetoresistive ratios (MR ratios) greater than that of Permalloy have been desired to cope with increases in linear density and track density in magnetic recording or increases in the resolving power of magnetic sensors.
Recently, a phenomenon called giant magnetoresistive effect has been found in a multilayer thin-film structure, such as a multilayer thin-film structure consisting of alternate layers of Fe thin films and Cr thin films or alternate layers of Co thin films and Cu thin films. In such a multilayer thin-film structure, the magnetizations of the ferromagnetic layers of Fe or Co interact magnetically through the nonmagnetic layers of Cr or Cu and the magnetizations of the stacked ferromagnetic layers are coupled to maintain an antiparallel alignment; that is, in this multilayer thin-film structure, the directions of magnetization of the ferromagnetic layers spaced alternately with the nonmagnetic layers are opposite to each other without an external magnetic field. When an appropriate external magnetic field is applied to such a structure, the magnetization directions of the ferromagnetic layers are aligned in a direction.
In this multilayer thin-film structure, it is known that the state where the magnetizations of the ferromagnetic layers in an antiparallel alignment and the state where the magnetizations of the ferromagnetic layers are in a parallel alignment differ from each other in the scattering mode of conduction electrons in the interface between the ferromagnetic Fe layers and the nonmagnetic Cr layers or between the ferromagnetic Co layers and the nonmagnetic Cu layers, depending upon the spins of the conduction electrons. Consequently, the electric resistance is high when the magnetization directions of the ferromagnetic layers are in an antiparallel alignment, the electric resistance is low when the magnetization directions of the ferromagnetic layers are in a parallel alignment, which produces the so-called giant magnetoresistive effect causing a resistance change at a high percentage ratio greater than that of resistance change in a Permalloy thin film. Thus, these multilayer thin-film structures have an MR producing mechanism basically different from that of the conventional single NiFe film.
However, since the magnetic interaction,.between the ferromagnetic layers of those multilayer thin-film structures that acts in an effort to set the magnetizations of the ferromagnetic layers in an antiparallel alignment is excessively strong, a very intense external magnetic filed must be applied to those multilayer thin-film structures to set the magnetization directions of the ferromagnetic layers in a parallel alignment. Therefore, a large resistance change cannot be expected unless a very intense magnetic field is applied to the multilayer thin-film structures, and hence magnetic heads that detect an applied magnetic field of a very low intensity created by a magnetic recording medium are unable to function with satisfactorily high sensitivity when such a multilayer thin-film structure is incorporated into those magnetic heads.
It may be effective, for solving such problems, to determine the thickness of the nonmagnetic layers of Cr or Cu so that the magnetic interaction between the ferromagnetic layers are not excessively strong and to control the relative magnetization directions of the ferromagnetic layers by another means other than the magnetic interaction.
A technique proposed to control the relative magnetization directions of the ferromagnetic layers employs an antiferromagnetic layer, such as an FeMn layer, to fix the magnetization direction of one of the ferromagnetic layers so that the magnetization direction of the same ferromagnetic layer may not be changed by an external magnetic field, and to allow the magnetization direction of the other ferromagnetic layer to change to enable the multilayer thin-film structure to be operated by an applied magnetic field of a very low intensity.
FIG. 22
shows a magnetoresistive sensor disclosed in U.S. Pat. No. 5,159,513 employing the foregoing technique. The magnetoresistive sensor A shown in
FIG. 22
is formed by depositing a first magnetic layer
2
, a nonmagnetic spacer
3
, a second magnetic layer
4
and an antiferromagnetic layer
5
on a nonmagnetic substrate
1
. The magnetization direction B of the second magnetic layer
4
is fixed by the magnetic exchange coupling effect of the antiferromagnetic layer
5
, and the magnetization direction C of the first magnetic layer
2
is kept perpendicular to the magnetization direction B of the second magnetic layer
4
in the absence of an applied magnetic field. However, since the magnetization direction C of the first magnetic layer
2
is not fixed, the magnetization direction C can be rotated by an applied external magnetic field.
When a magnetic field h is applied to the MR sensor shown in
FIG. 22
, the magnetization direction C of the first magnetic layer
2
rotates as indicated by the arrows according to the direction of the applied magnetic field h and, consequently, the first magnetic layer
2
and the second magnetic layer
4
become different from each other in magnetization rotation causing a resistance change that enables the detection of the applied magnetic field.
FIG. 23
shows another example of magnetoresistive sensors having the structure in which one magnetic layer has a fixed magnetization direction, the other magnetic layer having a free magnetization direction. As shown in
FIG. 23
, the MR-sensor B is formed by sequentially depositing an antiferromagnetic layer
7
of NiO, a magnetic layer
8
of Ni—Fe, a nonmagnetic metallic layer
9
of Cu, a magnetic layer
10
of Ni—Fe, a nonmagnetic metallic layer
11
of Cu, a magnetic layer
12
of Ni—Fe, and an antiferromagnetic layer
13
of FeMn in that order on a substrate
6
.
In this structure, the antiferromagnetic layers
7
and
13
fix the magnetization directions of the adjacent ferromagnetic layers
8
and
12
, and the magnetization direction of the ferromagnetic layer
10
sandwiched between the nonmagnetic layers
9
and
11
and disposed between the ferromagnetic layers
8
and
12
rotates according to the direction of an applied external magnetic field.
In the magnetoresistive sensor having the structure shown in
FIG. 22
or
23
, the resistance of the magnetoresistive sensor A or B varies linearly with high sensitivity with a small variation of the applied magnetic field. When the first magnetic layer
2
is formed of a soft magnetic material, such as Ni—Fe alloy, the MR sensor has the advantages in that the soft magnetic characteristics thereof can be used, and hysteresis is low.
The magnetoresistive sensor shown in
FIG. 22
has the structure in which the antiferromagnetic layer
5
fixes the magnetization of the adjacent second magnetic layer
4
, the second magnetic layer
2
having free magnetization. The magnetoresistive sensor shown in
FIG. 23
has the structure in which the upper and lower antiferromagnetic layers
7
an
13
of FeMn and NiO, respectively, fix the magnetizations of the ferromagnetic metallic layers
8
and
12
disposed therebetween, the magnetic layer
10
having free magnetization. These magnetoresistive sensors thus have the limitation of the number of the interfaces between NiFe (magnetic layer) and Cu (nonmagnetic metallic layer) and the problem of limiting the MR ratio.
The FeMn alloy used as the material for forming the antiferromagnetic layers
5
and
7
has unfavorable problems with respect to corro
Hasegawa Naoya
Koike Fumihito
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Kiliman Leszek
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