Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1997-10-06
2001-09-25
Ometz, David L. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06295186
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sensor comprising a magnetoresistive element and used as a magnetic head, a potentiosensor, an angular sensor, and the like, a manufacturing method thereof and a magnetic head comprising the sensor.
2. Description of the Related Art
As magnetoresistive reading heads (MR heads), AMR (Anisotropic Magnetoresistive) heads using the anisotropic magnetoresistive effect, and GMR (Giant Magnetoresistive) heads using spin dependent scattering are conventionally known. An example of the GMR heads is the spin-valve head disclosed in U.S. Pat. No. 5,159,513 in which high magnetoresistance is exhibited in a low magnetic field.
FIGS. 10 and 11
are drawings respectively showing the schematic constructions of AMR head element structures.
The head element shown in
FIG. 10
comprises an insulation layer
2
and a ferromagnetic layer (AMR material layer)
3
which are laminated on a soft magnetic layer
1
, antiferromagnetic layers
4
which are laminated on both ends of the ferromagnetic layer
3
with a space therebetween that is substantially equal to a track width, and electrically conductive layers
5
respectively laminated on the antiferromagnetic layers
4
. The head element shown in
FIG. 11
comprises a soft magnetic layer
1
, an insulation layer
2
and a ferromagnetic layer
3
which form a laminate, hard magnetic layers
6
provided on both sides of the laminate to hold it therebetween, and electrically conductive layers
5
respectively provided on the hard magnetic layers
6
.
For optimum operation of such AMR heads, two magnetic bias fields are required for the ferromagnetic layer
3
exhibiting the AMR effect.
A first magnetic bias field functions to make the resistance of the ferromagnetic layer
3
change in linear response to a magnetic flux from a magnetic recording medium. The first magnetic bias field is perpendicular (in the Z direction shown in
FIG. 1
) to the surface of the magnetic recording medium and parallel to the film surface of the ferromagnetic layer
3
. The first magnetic bias field is generally referred to as a “lateral bias” and can be obtained by flowing a sensing current through the ARM head element from the electrically conductive layers
5
.
A second magnetic bias field is generally referred to as a “longitudinal bias” and applied in parallel (in the X direction shown in
FIG. 1
) with the film surface of the ferromagnetic layer
3
. The longitudinal magnetic bias field is applied for suppressing the Barkhausen noise generated due to the formation of many magnetic domains in the ferromagnetic layer
3
, i.e., causing the resistance to smoothly change with the magnetic flux from the magnetic recording medium with less noise.
However, in order to suppress the Barkhousen noise, it is necessary to put the ferromagnetic layer into a single magnetic domain state. As a method of applying the longitudinal bias for this purpose, the following two methods are generally known. A first method uses the head element structure shown in
FIG. 11
in which the hard magnetic layers
6
are disposed on both sides of the ferromagnetic layer
3
to employ a leakage magnetic flux from the hard magnetic layers
6
. A second method uses the head element structure shown in
FIG. 10
in which the exchange anisotropic magnetic field developed in the contact boundary surfaces between the antiferromagnetic layers
4
and the ferromagnetic layer
3
is employed.
As an element structure which employs exchange anisotropic coupling due to the antiferromagnetic layers, the exchange bias structure shown in
FIG. 12
, and the spin-valve structure shown in
FIG. 13
are known.
The structure shown in
FIG. 12
is classified as the structure shown in
FIG. 10
, and comprises a ferromagnetic layer
22
, a non-magnetic layer
23
and a ferromagnetic layer
24
exhibiting the magnetoresistive effect which are laminated on a lower insulation layer
21
, antiferromagnetic layers
25
and lead layers
26
which are provided on both sides of the ferromagnetic layer
24
with a space substantially equal to the track width TW, and an upper insulation layer
27
provided on these layers.
In the structure shown in
FIG. 12
, a longitudinal bias is applied to the ferromagnetic layer
24
due to the exchange anisotropic coupling in the boundaries between the ferromagnetic layer
24
and the antiferromagnetic layers
25
to put regions B (the regions where the ferromagnetic layer
24
contacts the antiferromagnetic layers
25
) shown in
FIG. 12
into a single magnetic domain state in the X direction. This brings region A of the ferromagnetic layer
24
within the track width into a single magnetic domain state in the X direction. A sensing current is supplied to the ferromagnetic layer
24
from the lead layers
26
through the antiferromagnetic layers
25
. When the sensing current is supplied to the ferromagnetic layer
24
, a lateral magnetic bias field in the Z direction is applied to the ferromagnetic layer
24
due to the magnetostatic coupling energy from the ferromagnetic layer
22
. In this way, when the leakage magnetic field is applied to the ferromagnetic layer
24
magnetized by the longitudinal magnetic bias field and the lateral magnetic bias field from the magnetic recording medium, the electric resistance to the sensing current linearly responds to the magnitude of the leakage magnetic field and changes in proportion thereto. Therefore, the leakage magnetic field can be sensed by a change in the electric resistance.
The structure shown in
FIG. 13
comprises a free ferromagnetic layer
28
, a non-magnetic electrically conductive layer
29
and a ferromagnetic layer
24
which are laminated to form a magnetoresistive element
19
, and an antiferromagnetic layer
25
and an upper insulation layer
27
which are laminated in turn on the ferromagnetic layer
24
.
In the structure shown in
FIG. 13
, the sensing current is supplied to the magnetoresistive element
19
. The magnetization of the ferromagnetic layer
24
is fixed in the Z direction due to exchange anisotropic coupling with the antiferromagnetic layer
25
. Therefore, when a leakage magnetic field is applied from a magnetic recording medium which is moved in the Y direction, the electric resistance of the magnetoresistive element
19
changes with a change in the magnetization direction of the free ferromagnetic layer
28
, and the leakage magnetic field can thus be sensed by this change in the electric resistance.
Other known structures for optimum operation of the above structures by employing the spin valve structure include the structure shown in
FIG. 14
which comprises a free ferromagnetic layer
7
, a non-magnetic buffer layer
8
, a pinned ferromagnetic layer
9
and an antiferromagnetic layer
10
, which are laminated in turn to form a laminate, hard magnetic layers
11
which are provided on both sides of the laminate, and electrically conductive layers
12
respectively provided on the hard magnetic layers
11
, and the structure shown in
FIG. 15
which comprises a free ferromagnetic layer
7
, a non-magnetic buffer layer
8
, a pinned ferromagnetic layer
9
and an antiferromagnetic layer
10
, which are laminated in turn to form a laminate, an electrically conductive layer
12
and an antiferromagnetic layer
13
which are provided on the upper and lower sides of the laminate to hold it therebetween at either side thereof, and a buffer layer
14
provided adjacent to the whole laminate.
In the structure shown in
FIG. 14
, it is necessary that the magnetization direction of the free ferromagnetic layer
7
is directed in the track direction (the X direction shown in
FIG. 14
) in the state where a bias in the track direction is applied to the free ferromagnetic layer
7
to put it into a single magnetic domain state by the hard magnetic layers
11
, and that the magnetization direction of the pinned ferromagnetic layer
9
is directed in the Z direction shown in
FIG. 14
, i.e., the direction perpendicular to the magnetizat
Hasegawa Naoya
Makino Akihiro
Saito Masamichi
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Ometz David L.
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