Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of biasing or erasing
Reexamination Certificate
2000-08-16
2002-10-08
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of biasing or erasing
C360S046000, C360S324110
Reexamination Certificate
active
06462897
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a head device for use in a magnetic disk storage apparatus and particularly, a read head provided with a spin-valve magnetoresistive (MR) element.
Recently, a hard disk drive (HDD) includes a head for reading and writing data on a disk(s) which comprises a write head incorporating an inductive film head and a read head incorporating an MR (magnetoresistive) head.
The MR head includes an MR element having a magnetoresistive effect to a magnetic field (the signal magnetic field derived from a disk) and thus has several times characteristic higher in the reproducing output than an inductive film head. Recently, an improved type of the MR head has been focused including a spin-valve MR element is provided with spin-valve layers. Such an improved MR head is known as a GMR (giant magnetoresistive) head.
Referring to
FIG. 16
, a spin-valve layer structure
160
is made of a four-layer construction. More specifically, a non-magnetic layer (a conductive layer)
163
is sandwiched between two magnetic layers
161
and
162
and an antiferromagnetic layer
164
also called an exchange layer is provided on the magnetic layer
161
. The antiferromagnetic layer
164
has a function for determining the magnetization of the magnetic layer
161
in one direction. The magnetic layer
161
is thus called a pinning layer. The magnetic layer
162
is a soft magnetic layer of which magnetizing direction is determined by an external signal magnetic field from the outside (namely, a disk) and also called a free layer (or a magnetic field detecting layer).
The principle of action in the spin-valve layer
160
is explained referring to
FIGS. 17A and 17B
.
As shown in
FIG. 17A
, the spin-valve layer
160
produces a parallel magnetizing alignment where the magnetizing direction
171
of the free layer
162
aligns with the magnetizing direction
172
of the pinning layer
161
. In the alignment, electrons
173
can freely travel between the free layer
162
and the non-magnetic layer
163
thus decreasing the overall resistance of the spin-valve layer
160
. Also, there is produced an antiparallel magnetizing alignment where the magnetizing direction
171
of the free layer
162
is opposite to the magnetizing direction
172
of the pinning layer
161
, as shown in FIG.
17
B. In this case, the electrons
173
are dispersed between the free layer
162
and the non-magnetic layer
163
, hence sharply increasing the overall resistance of the spin-valve layer
160
. Accordingly, a rate of resistance change (a resistance change rate) is increased to several times higher than that of a conventional (form anisotropic) MR head, which is known as a GMR effect. The spin-valve layer
160
having such a GMR effect is now favorable for use as a primary element in a next-generation MR head (or a GMR head) for recording and reproducing a high density record.
FIG. 18
is a schematic view of a normal arrangement of a read/write head
2
using the spin-valve layer
160
. The read/write head comprises mainly of a read head
180
and a write head
181
mounted separately. The read head
180
is a GMR head having the spin-valve layer
160
. The spin-valve layer
160
is sandwiched between an upper shield member
182
and a lower shield member
183
for protection from the magnetic fields generated by adjacent data. The upper shield member
182
also functions as a lower electrode for the write head
181
as explained later. The distance between the two shield members
182
and
183
is a read gap RG of the read head
180
. In addition, a pair of hard magnets
184
a
and
184
b
are provided with ferromagnetic layers (or semi-ferromagnetic layers) for determining the magnetization of the free layer
162
in one direction, on both sides of the spin-valve layer
160
. The spin-valve layer
160
is connected by the hard magnets
184
a
and
184
b
to leads
185
a
and
185
b
respectively.
The write head
181
includes a coil
186
made of a spiral pattern form of a conductive material. The pattern form of the coil
186
is encapsulated by an insulating material
187
such as alumina (Al
2
O
3
). The coil
186
generates a magnetic field across a write gap WG, when supplied with a (write) current for data write action. A ring by the coil
186
extends through a tubular space defined by an upper electrode
188
and the lower electrode (or the upper shield member of the read head
180
)
182
. The foregoing element structure is fabricated by a head manufacturing process in which a thin film forming method is applied on a substrate
189
of the head forming a slider.
For using the read/write head as a magnetic head device in an HDD, it is desired that the resistance change in the spin-valve layer
160
of the read head is proportional to a leak magnetic flux (of the signal magnetic field) from a disk or a magnetic storage medium in the HDD (see the H-R characteristic curve shown in FIG.
19
). As shown in
FIG. 19
, the read head having the spin-valve layer
160
is designed so that the magnetizing direction
201
of the pinning layer
161
is vertical to (a signal magnetic field
190
of) the disk located in its opposite position and the magnetizing direction
202
(at the initial state) of the free layer
162
is parallel to the disk, producing an orthogonal magnetizing alignment state (referred to as HEAD-A). More particularly, the magnetizing directions
201
and
202
of the two layers
161
and
162
are at a right angle to each other, hence allowing the magnetizing direction
202
of the free layer
162
to be (magnetically) shifted in proportion to a magnitude of the leak magnetic field
190
from the disk and thus the spin-valve layer
160
to be varied in the resistance value corresponding to an angle of the shift (for example, a degree defined between the direction
202
and a direction
200
).
The antiferrormagnetic layer
164
which is a primary member in the spin-valve layer
160
is omitted in FIG.
19
.
FIG. 19
also shows H-R characteristic in a parallel magnetizing state (HEAD-B) and an antiparallel magnetizing state (HEAD-C) for comparison with the favorable state HEAD-A.
As described, it is essential in the read head (a GMR head) of the HDD that the pinning layer
161
of the spin-valve layer
160
has its magnetizing direction determined vertically to the disk. Meanwhile, the magnetizing direction of the pinning layer
161
is controlled and maintained by an exchange magnetic field on the antiferrormagnetic layer
164
. The magnitude (or intensity) of the exchange magnetic field is decreased with temperature and becomes zero when the temperature is a predetermined degree which is known as a blocking temperature. The blocking temperature of the antiferromagnetic layer made generally of an (Fe—Mn) alloy of iron and manganese is 150° C. When the ambient temperature about the spin-valve layer 160° C. exceeds 150° C., the magnetizing direction of the pinning layer
161
is shifted.
Also, it is proved in a process of manufacturing a GMR head, a process of assembling the GMR head in an HDD, or an action of the HDD having the GMR head that the magnetizing direction of the pinning layer
161
in the spin-valve layer
160
is likely to shift due to any combination of the following four factors (1) to (4).
(1) Ambient temperature
As described, when the GMR head is operated at a temperature exceeding the blocking temperature or the ambient temperature about the spin-valve layer
160
after determining magnetizing direction, exceeds the blocking temperature, the magnetizing direction of the pinning layer
161
may be shifted. With the GMR head assembled in an HDD, the temperature in the HDD is increased more or less to 20° C. due to heat generated by electric circuits and a motor. Generally, the temperature allowing a proper action of the HDD is about 60° C. The MR head (including GMR head) is fed with an operating current which is also called a sense current. Since the sense current generates heat, the temperature in the HDD is increased up to 40° C. Depen
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