Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-06-13
2004-10-19
Davis, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06807034
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetic sensing elements of a current-perpendicular-to-the-plane (CPP) type. More particularly, the invention relates to a magnetic sensing element in which the rate of change in resistance can be improved and a high read-sensitivity and a high output can be obtained, and to a thin-film magnetic head including the magnetic sensing element.
2. Description of the Related Art
FIG. 14
is a partial sectional view which shows the structure of a conventional magnetic sensing element, viewed from the surface facing a recording medium.
In the magnetic sensing element shown in
FIG. 14
, an antiferromagnetic layer (lower antiferromagnetic layer)
4
composed of a PtMn alloy or the like is formed on an underlayer
6
composed of Ta or the like. A pinned magnetic layer (lower pinned magnetic layer)
3
composed of an NiFe alloy or the like is formed on the antiferromagnetic layer
4
, and a nonmagnetic interlayer (lower nonmagnetic interlayer)
2
composed of Cu or the like is formed on the pinned magnetic layer
3
. A free magnetic layer
1
composed of an NiFe alloy or the like is formed on the nonmagnetic interlayer
2
.
Another nonmagnetic interlayer (upper nonmagnetic interlayer)
2
, another pinned magnetic layer (upper pinned magnetic layer)
3
, and another antiferromagnetic layer (upper antiferromagnetic layer)
4
are deposited on the free magnetic layer
1
in that order. A protective layer
7
composed of Ta or the like is formed on the upper antiferromagnetic layer
4
.
The layers from the underlayer
6
to the protective layer
7
together constitute a multilayer film
10
. Hard bias layers
5
are formed on both sides in the track width direction (in the X direction in the drawing) of the multilayer film
10
, and electrode layers
11
are formed on the hard bias layers
5
.
This magnetic sensing element is a so-called “dual spin-valve thin-film element” in which the pinned magnetic layer
3
and the antiferromagnetic layer
4
are disposed on each surface of the free magnetic layer
1
with the nonmagnetic interlayer
2
therebetween.
In the magnetic sensing element shown in
FIG. 14
, the magnetization direction of the pinned magnetic layer
3
is pinned in the height direction (in the Y direction in the drawing) by an exchange coupling magnetic field generated between the pinned magnetic layer
3
and the antiferromagnetic layer
4
. The magnetization direction of the free magnetic layer
1
is aligned in the track width direction (in the X direction) by a longitudinal bias magnetic field from the hard bias layer
5
.
In the dual spin-valve thin-film element shown in FIG.
14
, since the number of interfaces at which electron scattering occurs is twice as many as a single spin-valve thin-film element which includes an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic interlayer, and free magnetic layer, each one layer, an improvement in the rate of change in resistance is expected.
In the magnetic sensing element shown in
FIG. 14
, a sensing current flows substantially parallel to the planes of the individual layers of the multilayer film
10
, that is, the element is referred to as a “current-in-the-plane (CIP)” type element.
On the other hand, an element in which a sensing current flows perpendicular to the individual layers of the multilayer film
10
is referred to as a “current-perpendicular-to-the-plane (CPP)” type element.
When the element is miniaturized as the recording density is increased, and in particular, when the area of an element in the direction parallel to the planes of the individual layers is decreased to 0.1 &mgr;m square or less, it is known that the read output can be increased by selecting the CPP type instead of the CIP type.
Therefore, in order to improve both the read output and the rate of change in resistance as the recording density is further increased in future, a magnetic sensing element of a CPP type having a dual structure is thought to be desirable.
FIG. 15
is a schematic diagram showing a structure of a CPP-type dual spin-valve thin-film element.
The giant magnetoresistance (GMR) effect in a magnetic sensing element is mainly caused by “spin-dependent scattering” of electrons. That is, the GMR effect is obtained by using the difference between the mean free path &lgr;
+
of the conduction electrons (e.g., spin-up electrons) having a spin parallel to the magnetization direction of a magnetic material, i.e., herein, a free magnetic layer, and the mean free path &lgr;
−
of the conduction electrons (e.g., spin-down electrons) having a spin antiparallel to the magnetization direction of the free magnetic layer.
In the CPP-type magnetic sensing element, since the current flows perpendicular to the planes of the individual layers, the length of the current path of the sensing current flowing through a free magnetic layer, a nonmagnetic interlayer, and a pinned magnetic layer, which participate in the magnetoresistance effect, is shorter compared to the CIP-type magnetic sensing element in which the sensing current flows substantially parallel to the planes of the individual layers.
Therefore, if the thickness of the pinned magnetic layer and the thickness of the free magnetic layer are small, the conduction electrons, for example, spin-down electrons, which are not supposed to pass through the magnetic layers in the CIP type, pass through the magnetic layers together with the spin-up conduction electrons in the CPP type. It is not possible to increase the difference between the mean free path &lgr;
+
of the spin-up conduction electrons and the mean free path &lgr;
−
of the spin-down conduction electrons, and the rate of change in resistance cannot be improved.
Although an attempt has been made to improve the rate of change in resistance by increasing the thickness of the pinned magnetic layer and the thickness of the free magnetic layer so that the bulk scattering effect is satisfactorily displayed, if the thickness of the free magnetic layer is increased, variations in the magnetization of the free magnetic layer in response to an external magnetic field become dull because of an increase in the magnetic moment.
The magnetic moment of the free magnetic layer is determined by the product of the saturation magnetization Ms and the thickness t1. The magnetic moment is an index of variability of the magnetization of the magnetic layer in response to an external magnetic field. That is, if the magnetic moment is increased, variability of the magnetization of the magnetic layer having the magnetic moment in response to the external magnetic field is weakened.
In the magnetic sensing element, the magnetization of the pinned magnetic layer is pinned in a predetermined direction and the magnetization of the free magnetic layer varies in response to an external magnetic field, resulting in a change in the electrical resistance, and thereby external signals are detected. Therefore, the magnetization of the free magnetic layer must vary with the external magnetic field sensitively. In the CPP type, however, if the thickness of the free magnetic layer is increased to display the bulk scattering effect, the magnetic moment of the free magnetic layer is increased, and as a result, the sensitivity to the external magnetic field is decreased and it is not possible to improve the read output appropriately.
As described above, in the conventional CPP-type magnetic sensing element, it is not possible to improve both the read output and the rate of change in resistance simultaneously.
With respect to the CPP-type dual spin-valve thin-film element, since the number of layers can be increased and the number of the interfaces at which electron scattering occurs is increased compared to the single spin-valve thin-film element, an improvement in the rate of change in resistance is expected. However, a further improvement in the rate of change in resistance is desired to meet the demands for higher recording densities.
SUMMARY OF THE INV
Hasegawa Naoya
Umetsu Eiji
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Davis David
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