Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-08-17
2002-03-05
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192150, C427S372200, C427S130000
Reexamination Certificate
active
06352621
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spin-valve type magnetoresistive sensor wherein electrical resistance is changed depending on the relationship between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer affected by an external magnetic field. More particularly, the present invention relates to a spin-valve type magnetoresistive sensor which has higher sensitivity of detection and is adaptable for high-density recording as the result of an improvement in structure and material properties of a spin-valve film laminate, as well as to a spin-valve type magnetoresistive head using the sensor.
2. Description of the Related Art
There are known spin-valve type and multilayer type as laminated structures capable of developing a GMR (Giant Magnetoresistive) effect.
FIG. 12
is a sectional view showing a conventional multilayer type GMR sensor.
The multilayer type GMR sensor has a laminated structure comprising pairs of a ferromagnetic material layer
9
and a non-magnetic electrically conductive layer
2
which are formed in plural number repeatedly from the bottom.
Generally, the ferromagnetic material layer
9
is made of a NiFe (nickel—iron) alloy or a CoFe (cobalt—iron) alloy, and the non-magnetic electrically conductive layer
2
is made of Cu (copper).
The ferromagnetic material layers
9
are positioned over and under the non-magnetic electrically conductive layer
2
in a laminated structure. Particularly, when the non-magnetic electrically conductive layer
2
is formed in a thickness on the order of 10-20 angstroms, the upper and lower ferromagnetic material layers
9
are magnetized into a single domain state in anti-parallel relation uniformly due to the RKKY interaction.
In the multilayer type GMR sensor, when the sensor is subject to a leakage magnetic field from a magnetic recording medium such as a hard disk, the magnetization direction of the ferromagnetic material layer
9
is varied to the same direction as the leakage magnetic field. A variation in the magnetization direction of the ferromagnetic material layer
9
changes electrical resistance, and this change in value of the electrical resistance results in a voltage change. The leakage magnetic field from the magnetic recording medium is detected based on the resulting voltage change.
Meanwhile, a magnetoresistance ratio (MR ratio) of the multilayer type GMR sensor amounts to the order of about 10-30% when an external magnetic field is in the range of several tens Oe (oersted) to several thousands Oe. The reason why the magnetoresistance ratio has a very large value is that there are a very large number of places where electrons scattering can occur. Further, a very strong external magnetic field is required to achieve such a high magnetoresistance ratio. This is because the magnetization direction of the ferromagnetic material layer
9
is firmly fixed in anti-parallel relation due to the RKKY interaction. It has been found from calculation of plane recording density based on the magnetoresistance ratio in the above range that the multilayer type GMR sensor is adaptable for the plane recording density up to value on the order of 100 Cb/in
2
. But it has also been confirmed that when a relatively weak external magnetic field on the order of several Oe is applied, the magnetoresistance ratio of the multilayer type GMR sensor becomes smaller than that of a spin-valve type magnetoresistive sensor.
FIG. 13
shows a conventional single spin-valve type magnetoresistive sensor. This sensor comprises four layers, i.e., a free magnetic layer
1
, a non-magnetic electrically conductive layer
2
, a pinned magnetic layer
3
and an antiferromagnetic layer
4
from the top. Numerals
5
,
5
on both sides denote hard bias layers. Denoted by
6
,
7
are respectively a buffer layer and a barrier layer made of non-magnetic material, such as Ta (tantalum), and
8
is an electrically conductive layer. The pinned magnetic layer
3
is selected to have a greater coercive force than the free magnetic layer
1
.
Because the pinned magnetic layer
3
and the antiferromagnetic layer
4
are formed in contact with each other, the pinned magnetic layer
3
is put into a single domain state in the Y-direction and has the magnetization direction fixed in the Y-direction under an exchange anisotropic magnetic field produced by exchange coupling at the boundary surface between the pinned magnetic layer
3
and the antiferromagnetic layer
4
. By heat-treating (annealing) the sensor under a magnetic field applied thereto, the exchange anisotropic magnetic field can be produced at the boundary surface between the pinned magnetic layer
3
and the antiferromagnetic layer
4
.
Also, the hard bias layers
5
magnetized in the X-direction affects the free magnetic layer
1
so that the magnetization direction of the free magnetic layer
1
is uniformly set in the X-direction. In other words, since the free magnetic layer
1
is put into a single domain state in the predetermined direction by the presence of the hard bias layers
5
, the occurrence of Barkhausen noise can be prevented.
In the above single spin-valve type magnetoresistive sensor, a steady electric current is applied from the electrically conductive layers
8
to the free magnetic layer
1
, the non-magnetic electrically conductive layer
2
and the pinned magnetic layer
3
. A magnetic recording medium such as a hard disk runs in the Z-direction. When a leakage magnetic field from the magnetic recording medium is applied to the sensor in the Y-direction, the magnetization direction of the free magnetic layer
1
is varied from the X-direction to the Y-direction. Thus, electrical resistance is changed depending on the relationship between a variation in the magnetization direction of the free magnetic layer
1
and the fixed magnetization direction of the pinned magnetic layer
3
. This change in value of electrical resistance result in a voltage change. The leakage magnetic field from the magnetic recording medium is detected based on the resulting voltage change.
FIG. 14
is a sectional view showing a conventional dual spin-valve type magnetoresistive sensor.
In the dual spin-valve type magnetoresistive sensor, non-magnetic electrically conductive layers
2
,
2
, pinned magnetic layers
3
,
3
and antiferromagnetic layers
4
,
4
are formed into laminated structures on both sides of a free magnetic layer
1
at the middle in vertically symmetric relation. The magnetization direction of the free magnetic layer
1
is uniformly set in the X-direction by the presence of hard bias layers
5
magnetized in the X-direction. Also, the pinned magnetic layers
3
,
3
are each put into a single domain state in the Y-direction and have the magnetization direction fixed in the Y-direction under an exchange anisotropic magnetic field produced by exchange coupling at the boundary surface between itself and the antiferromagnetic layer
4
.
When a leakage magnetic field from the magnetic recording medium is applied to the sensor in the Y-direction, the magnetization direction of the free magnetic layer
1
is varied from the X-direction to the Y-direction, whereupon a value of electrical resistance is changed.
In the spin-valve type magnetoresistive sensor, when the magnetization direction of the free magnetic layer
1
is varied from the X-direction to the Y-direction, electrons existing between the free magnetic layer
1
and the pinned magnetic layer
3
and tending to move from one to the other are scattered at the boundary surface between the non-magnetic electrically conductive layer
2
and the free magnetic layer
1
and at the boundary surface between the non-magnetic electrically conductive layer
2
and the pinned magnetic layer
3
. As a result, the value of electrical resistance is changed and the leakage magnetic field from the magnetic recording medium is detected based on the resulting voltage change.
The electrical resistance shows a maximum value when an angle
Saito Masamichi
Watanabe Toshinori
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Nguyen Nam
Ver Steeg Steven H.
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