Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2001-01-31
2002-06-04
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S075000, C360S313000, C324S212000
Reexamination Certificate
active
06400519
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a spin valve magnetoresistive effect type element assessment method and a spin valve magnetoresistive effect type element assessment device for assaying the magnetization state in a pinned layer in a spin valve magnetoresistive effect type element.
BACKGROUND ART
A spin valve magnetoresistive effect type element or an element called a spin valve element has been known as an element for a magnetic sensor.
The spin valve magnetoresistive effect type element is an element comprising, as shown in
FIG. 10
, a free layer
31
made of a ferromagnetic material (Ni—Fe, etc.), an intermediate layer
32
made of a non-magnetic metal material (typically, Cu), a pinned layer
33
made of a ferromagnetic material (Ni—Fe, etc.), and an antiferromagnetic layer
34
made of an antiferromagnetic material (Mn—Fe).
The spin valve magnetoresistive effect type element (hereinafter, referred to as the SV element) is an element that detects an external magnetic field by exploiting the fact that the element resistance varies considerably with a difference between the direction of magnetization in the free layer
31
and that in the pinned layer
33
, and used as a magnetic data reading element in an magnetic disk device, a magnetic tape device, a magnetic card reader, etc., for example.
The antiferromagnetic layer
34
in the SV element is a layer that prevents the direction of magnetization in the pinned layer
33
from being dependent on an external magnetic field (fixes the direction of magnetization to the initial direction). The intermediate layer
32
is a layer that weakens the exchange interaction between the free layer
31
and pinned layer
33
, and made thinner than the correlation length of conduction electrons. The free layer
31
is a layer, in which the direction of magnetization is free to change in response to an external magnetic field, and typically subjected to heat treatment in the magnetic field so as to have an easy axis that is perpendicular to the direction of magnetization in the pinned layer
33
.
Thus, the SV element detects a difference between the direction of magnetization in the free layer
31
and that in the pinned layer
33
caused by an external magnetic field as variance in resistance. Therefore, detectability of magnetic field is affected considerably by the magnetization state in the pinned layer
33
. Also, because the magnetization state in the pinned layer
33
is fixed by the antiferromagnetic layer
34
, if a temperature raises above the Néel temperature at a portion within the antiferromagnetic layer
34
, there may occur inconveniences such that the detectability of magnetic field is degraded, or the SV element no longer functions as the magnetic field detecting element.
More specifically, given that the magnetization state in the pinned layer
33
and the &rgr;-H characteristics of the SV element immediately after the manufacturing are as those shown in FIGS.
11
(
a
) and
11
(
b
), respectively, if the magnetization state in the pinned layer
33
changes to the one as shown in FIG.
12
(
a
) in a use, then the &rgr;-H characteristics may change correspondingly to the one as shown in
FIG. 12
(
b
). Further, if the direction of magnetization in the pinned layer
33
is completely inversed as shown in
FIG. 13
(
a
), then the &rgr;-H characteristics of the SV element may change correspondingly to the one as shown in
FIG. 13
(
b
).
As a preventive technique against such characteristics deterioration caused by a change of the magnetization state in the pinned layer
33
, U.S. Pat. No. 5,650,887 discloses a magnetic disk device and a magnetic field sensor for, when the &rgr;-H characteristics of the SV element are deteriorated, providing the pinned layer with circumstances (magnetic field and temperature) capable of restoring the magnetization state to the initial state by allowing a current of a predetermined pattern to pass through.
According to the magnetic disk device disclosed in the above publication, deterioration of the &rgr;-H characteristics of the SV element provided in a magnetic head is detected by an increase in an error rate. Also, the magnetic field sensor detects deterioration of the &rgr;-H characteristics by a drop in an output from the sensor.
By using the aforementioned technique, it is possible to restore the characteristics of the SV element that have been deteriorated in response to a change of the magnetization state in the pinned layer. However, if the characteristics of the SV element are deficient from the start, it is impossible to upgrade such deficient characteristics to the standards. In other words, an SV element may be produced, in which the magnetization in the pinned layer
33
is not inversed, but the gradient of the &rgr;-H characteristics is smaller than a typical one.
Adapting the foregoing technique to such an SV element, however, cannot upgrade the characteristics of the SV element to the standards by means of current passing treatment. On the contrary, this causes a magnetic disk device or a magnetic field sensor to trigger the current passing treatment in response to a slight inversion of the magnetization (trigger the current passing treatment frequently). Also, incorporating a magnetic head employing such an SV element in a normal magnetic disk device could only result in a magnetic disk device with strong likelihood of becoming incapable of reading data.
The present invention is devised to solve the above problems, and therefore, has an object to provide a spin valve magnetoresistive effect type element assessment method and a spin valve magnetoresistive effect type element assayer, which can assessment the existence of an area in the pinned layer in the spin valve magnetoresistive effect type element where the magnetization has been inversed.
DISCLOSURE OF THE INVENTION
According to a spin valve magnetoresistive effect type element assessment method of the present invention, a resistance value of a spin valve magnetoresistive effect type element is measured while a relative location correlation between the spin valve magnetoresistive effect type element and a magnetic field having a predetermined intensity distribution is adjusted. Then, a magnetization state in a pinned layer in the spin valve magnetoresistive effect type element is assayed based on a correlation between the relative location correlation and resistance value obtained from measuring.
In other words, it is difficult to find directly the magnetization state (position, width, etc. of a portion where magnetization is inverted) in the pinned layer by the relative location correlation between the SV element and magnetic field and the correlation between the SV element and resistance value obtained from the foregoing measuring. However, it is easy to compute a correlation that would be measured by presuming the magnetization state in the pinned layer.
Hence, by measuring the relative location correlation between the SV element and magnetic field and the correlation between the SV element and resistance value like in the present invention, it is possible to presume the magnetization state and the width and position of a magnetization inverted area in the pinned layer from similarity with the correlation obtained by means of computation and the correlation obtained by means of measurement.
In addition, a spin valve magnetoresistive effect type element assessment device of the present invention is a device for assaying a magnetization state in a pinned layer in a spin valve magnetoresistive effect type element incorporated in a magnetic head, including: a magnetic disk having an assaying track, in which predetermined magnetic information is recorded; an actuator which maintains the magnetic head over the magnetic disk, the actuator also changes a distance between the magnetic head and a rotation center of the magnetic disk; and a position dependency data measuring and outputting unit which outputs position dependency data representing position dependency of a resistance value of the spin valve magnet
Faber Alan T.
Fujitsu Limited
Greer Burns & Crain Ltd.
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