Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1998-12-09
2003-10-14
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06633464
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to magnetic disk data storage systems, more particularly to magnetoresistive (MR) read heads, and most particularly to structures incorporating an Fe/FeSi/Fe synthetic antiferromagnetic (AFM) pinned layer and methods for making same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In
FIGS. 1A and 1B
, a magnetic disk data storage systems
10
of the prior art includes a sealed enclosure
12
, a disk drive motor
14
, a magnetic disk
16
, supported for rotation by a drive spindle S
1
of motor
14
, an actuator
18
and an arm
20
attached to an actuator spindle S
2
of actuator
18
. A suspension
22
is coupled at one end to the arm
20
, and at its other end to a read/write head or transducer
24
. The transducer
24
typically includes an inductive write element with a sensor read element (which will be described in greater detail with reference to FIG.
1
C). As the motor
14
rotates the magnetic disk
16
, as indicated by the arrow R, an air bearing is formed under the transducer
24
causing it to lift slightly off of the surface of the magnetic disk
16
, or, as it is termed in the art, to “fly” above the magnetic disk
16
. Alternatively, some transducers, known as “contact heads,” ride on the disk surface. Various magnetic “tracks” of information can be read from the magnetic disk
16
as the actuator
18
causes the transducer
24
to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 1C
depicts a magnetic read/write head
24
including a write element
26
and a read element
28
. The edges of the write element
26
and read element
28
also define an air bearing surface ABS, in a plane
29
, which faces the surface of the magnetic disk
16
.
The write element
26
is typically an inductive write element. A write gap
30
is formed between an intermediate layer
31
, which functions as a first pole, and a second pole
32
. Also included in write element
26
, is a conductive coil
33
that is positioned within an electrical insulator
34
, such as a cured photoresistive material. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk
16
.
The read element
28
includes a first shield
36
, the intermediate layer
31
, which functions as a second shield, and a read sensor
40
that is located between the first shield
36
and the second shield
31
. The most common type of read sensor
40
used in the read/write head
30
is the magnetoresistive sensor. A magnetoresistive (MR) sensor is used to detect magnetic field signals by means of a changing resistance in the read sensor. When there is relative motion between the MR sensor and a magnetic medium (such as a disk surface), a magnetic field from the medium can cause a change in the direction of magnetization in the read sensor, thereby causing a corresponding change in resistance of the read element. The change in resistance can be detected to recover the recorded data on the magnetic medium.
One type of conventional MR sensor utilizes the anisotropic magnetoresistive (AMR) effect for such detection, where the read element resistance varies in proportion to the square of the cosine of the angle between the magnetization in the read sensor and the direction of a sense current flowing through the read sensor. Another type of MR sensor uses a phenomenon known as the giant magnetoresistive (GMR) effect. In such devices, the read sensor resistance is independent of the sense current direction, but varies in proportion to the cosine of the angle between the magnetizations of nearby layers. In a spin valve GMR sensor, two ferromagnetic layers are separated by a non-magnetic metal layer, sometimes referred to as a spacer layer. One of the ferromagnetic layers is a “free” layer, whose magnetization can be moved by external magnetic fields. The other ferromagnetic layer is a “pinned” layer whose magnetization is set in a particular direction and resistant to changes of that direction by external magnetic fields. This pinning is typically achieved with an exchanged-coupled antiferromagnetic (AFM) layer adjacent to the pinned layer.
In
FIG. 2
, a view taken along line
2
—
2
of
FIG. 1C
(i.e., perpendicular to the plane
29
and therefore perpendicular to the air bearing surface ABS) illustrates the structure of the read sensor
40
, in the form of a spin valve read sensor of the prior art. The spin valve read sensor
40
includes a free layer
42
, a non-magnetic metal spacer layer
44
, and a pinned layer
46
which together form the sensing layers
47
. In addition, the read sensor
40
includes an antiferromagnetic (AFM) pinning layer
48
that pins the magnetization of the adjacent pinned layer
46
. The spin valve read sensor
40
is supported by a substrate
50
(which can be the first shield
36
) and a buffer layer
52
, while a capping layer (not shown) can be provided over the AFM layer
48
. Although not shown in
FIG. 2
, leads, typically made from gold or another low resistance material, route a sense current from a current source to the spin valve read sensor
40
, while signal detection circuitry detects changes in resistance of the read sensor
40
as it encounters magnetic fields.
The free and pinned layers
42
and
46
are typically made from a soft ferromagnetic material such as Permalloy, while the non-magnetic metal spacer layer
44
can be formed of copper (Cu). The pinning layer
48
is formed of an antiferromagnetic (AFM) material that is used to set the magnetic direction of the pinned layer
46
, preventing the magnetization of the pinned layer
46
from rotating under most operating conditions. The antiferromagnetic material of the pinning layer
48
can be, for example, a manganese (Mn) alloy such as iron-manganese (FeMn) or an oxide such as nickel-oxide (NiO).
The function of the pinned layer
46
can be better understood with reference to the magnetization directions depicted in FIG.
2
. The pinned layer
46
is magnetized as indicated by the arrow
43
. Alone, the free layer
42
may have an initial magnetization as indicated by the dashed arrow
45
. However, in a spin valve such as that depicted in
FIG. 2
, there is a magnetostatic coupling of the pinned layer
46
, a ferromagnetic exchange coupling through the non-magnetic metal spacer layer
44
, and a field generated by the sense current I. Thus, the free layer
42
can have an actual magnetization direction as illustrated by the arrow
41
(which appears as a point in
FIG. 2
because it is directed into the plane
29
), which is due to the sum of the initial magnetization
45
, the magnetostatic coupling of the pinned layer
46
, the ferromagnetic exchange coupling though the spacer layer
44
, and the field generated by the sense current I.
Other spin valve read sensors have been developed which use a multilayer pinned layer in place of the single pinned layer
46
of FIG.
2
. Such a pinned layer
46
′ is shown in
FIG. 3
, formed of a first ferromagnetic (FM) layer
54
that is separated from a second FM layer
55
by a non-magnetic spacer layer
56
. Specifically, such a read sensor has been developed with the first and second FM layers formed of cobalt and the spacer layer formed of ruthenium (Ru). The magnetization
57
of the first FM layer is set in a first direction, while the magnetization
58
of the second FM layer is set in a second direction that is substantially antiparallel to the first direction. The two FM layers are strongly antiferromagnetically coupled in an antiparallel orientation, and their magnetizations are pinned by the pinning layer
48
. Thus, the magnetization of the pinned layer
53
is significantly resistant to perturbation by the external magnetic fields used to change the magnetization
41
of the free layer
42
.
FIG. 4
is a graph of the saturation field (Hs) of a sp
Lai Chih-Huang
Miller Charles W.
Rottmayer Robert E.
Shi Zhupei
Tong Hua-Ching
Letscher George J.
Read-Rite Corporation
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