Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-09-21
2003-12-09
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324110
Reexamination Certificate
active
06661624
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to magnetoresistive devices used in a magnetic head for reading magnetized information from magnetic recording media, and, more particularly, to a spin-valve magnetoresistive device (hereinafter referred to simply as “SVMR device”) utilizing giant magnetoresistive (GMR) effects. A SVMR device is a highly-sensitive magnetoresistive device that detects a magnetoresistive value change in a magnetic layer caused by a minute external magnetic field, and has been attracting more and more attention as a reproduction unit used in a high-density magnetic recording apparatus.
2. Description of the Related Art
FIG. 1
shows the structure of a conventional SVMR device
100
. This SVMR device
100
comprises a free magnetic layer
101
formed from a ferromagnetic layer, a non-magnetic conductive layer
102
formed on the free magnetic layer
101
, a fixed magnetic layer
103
formed from a ferromagnetic layer on the non-magnetic conductive layer
102
, and an anti-ferromagnetic layer
104
formed on the fixed magnetic layer
103
. The SVMR device
100
shown in
FIG. 1
is a forward-direction laminated type that has a multi-layered structure formed by a thin-film forming technique starting from the bottom layer (which is the free magnetic layer
101
in this case). Also, a SVMR device of a reverse-direction laminated type, which is laminated starting from the anti-ferromagnetic layer
104
as the bottom layer, is known and basically has the same functions as the forward-direction laminated type. In this specification, the SVMR device
100
of the forward-direction laminated type will be described.
In
FIG. 1
, the magnetic direction of the free magnetic layer
101
is magnetically rotated by a signal magnetic field Hsig from a magnetic recording medium. As the relative angle between the magnetic direction of the free magnetic layer
101
and the magnetic direction of the fixed magnetic layer
103
changes, the magnetic resistance of the SVMR device
100
changes accordingly. When the SVMR device
100
is used as a magnetic head for reproduction, the magnetic direction of the fixed magnetic layer
103
is fixed in the height direction H of the SVMR device
100
. When no external magnetic field is applied, the magnetic direction of the free magnetic layer
101
is set in the width direction W of the device
100
and thus is perpendicular to the magnetic direction of the fixed magnetic layer
103
. While the magnetic direction of the free magnetic layer
101
is perpendicular to the magnetic direction of the fixed magnetic layer
103
, the signal magnetic field Hsig from the magnetic recording medium is in parallel with the magnetic direction of the fixed magnetic layer
103
or with the reverse direction of the magnetic direction of the fixed magnetic layer
103
, and is perpendicular to the magnetic direction of the free magnetic layer
101
. Accordingly, the magnetic resistance of the SVMR device
100
can be symmetrically detected. Such symmetrical magnetic resistance facilitates the signal processing in the magnetic recording apparatus, and the signal magnetic field Hsig from the magnetic recording medium can be reproduced with high precision.
However, a leakage magnetic field that tilts the magnetic direction of the free magnetic layer
101
exists in the vicinity of the SVMR device
100
. Examples of the leakage magnetic field having adverse influence upon the free magnetic layer
101
include a magnetic field generated from the end surface of the fixed magnetic layer
103
, an exchange-coupling with the anti-ferromagnetic layer generated between the fixed magnetic layer
103
and the free magnetic layer
101
, and a sense current magnetic field formed by a sense current that is applied to detect the magnetic resistance of the SVMR device
100
. Under the adverse influence of the leakage magnetic field, the magnetic direction of the free magnetic layer
101
deviates from the direction parallel with the width direction W toward the height direction H. As a result, the magnetic resistance variation of the SVMR device
100
in response to the signal magnetic field Hsig cannot be maintained in the symmetrical state.
To direct the magnetic direction of the free magnetic layer
101
into a parallel direction with the width direction W, a corrective magnetic field for correcting the deviation of the magnetic direction of the free magnetic layer
101
can be applied. In this specification, such a correction magnetic field for canceling a leakage magnetic field is referred to as a bias magnetic field, which is so set that the magnetic direction of the fixed magnetic layer
103
and the free magnetic layer
101
are perpendicular to each to other when no external magnetic field exists in the vicinity of the SVMR device
100
.
The size of the SVMR device
100
is determined by the density of a magnetic recorded material to be reproduced. Because of today's rapid increase in recording density, the distance between a magnetic recording medium and the signal magnetic field Hsig has been shrinking. To read the signal magnetic field Hsig accurately, it is necessary to reduce the width w of the SVMR device
100
. However, if the width w of the SVMR device
100
is smaller than the height h of the SVMR device
100
, the magnetic direction of the free magnetic layer
101
is liable to tilt into the height direction H due to shape anisotropy. Moreover, the height h needs to be reduced as the width w is reduced, since otherwise it is difficult for the signal magnetic field Hsig to enter in the height direction H.
Meanwhile, the SVMR device
100
that can be actually used in a magnetic head is submicron in size. With a smaller height h of the device
100
, the adverse influence of the leakage magnetic field from the fixed magnetic layer
103
is larger. Despite this effect, the height h of the device
100
is becoming smaller as the density of the magnetic recording medium is becoming higher. Accordingly, a magnetostatic leakage magnetic field from the fixed magnetic layer
103
becomes even stronger, and the magnetic direction of the free magnetic layer
101
liable to deviate into a direction parallel to the reverse direction of the magnetic direction of the fixed magnetic layer
103
.
Solutions have been suggested to eliminate the problems associated with a small height h of the device
100
. One of the solutions suggests a method in which the current direction is adjusted to generate a sense current magnetic field in such a direction that cancels a leakage magnetic field from the fixed magnetic layer
103
. However, a sense current of 45 MA/cm
2
can generate a magnetic field of only 10 Oe, for instance. In view of this, a great improvement in bias magnetic field cannot be expected from the sense current.
The magnetic quantity of the fixed magnetic layer
103
can be reduced, but the thickness of the fixed magnetic layer
103
is required to be greater than a certain thickness in order to maintain the magnetic characteristics of the SVMR device
100
.
Meanwhile, a technique in which a multi-layered structure is used in place of the conventional fixed magnetic layer has been suggested. The multi-layered structure includes a ferromagnetic layer, a reverse parallel coupling intermediate layer, and another ferromagnetic layer, which layers are laminated in that order. This multi-layered structure will be hereinafter referred to as “multi-layered fixed magnetic layers”. In this multi-layered fixed magnetic layer, the magnetic directions of the upper and lower ferromagnetic layers are reverse to each other, with the anti-parallel coupling intermediate layer being interposed. Accordingly, the upper and lower ferromagnetic layers cancel the magnetism of each other, and the leakage magnetic field applied to the free magnetic layer becomes smaller. Since the multi-layered fixed magnetic layer is normally formed by one magnetic material, the upper and lower ferromagnetic layers have the same thickness, which effect
Evans Jefferson
Fujitsu Limited
Greer Burns & Crain Ltd.
LandOfFree
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