Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-06-06
2003-02-04
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06515838
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
This invention relates generally to spin valve magnetic transducers for reading information signals from a magnetic medium and, in particular, to increasing the thickness of a pinned layer for a spin valve sensor, and to magnetic recording systems which incorporate such sensors.
2. The Relevant Technology
Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization of the MR element and the direction of sense current flowing through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor, more recently developed, is the giant magneto resistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using two layers of ferromagnetic material separated by a layer of non-magnetic electrically conductive material are generally referred to as spin valve (SV) sensors manifesting the GMR effect. In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., NiO or Fe—Mn) layer.
The magnetization of the other ferromagnetic layer, referred to as the frce layer, however, is not fixed and is free to rotate in response to the field from the recorded magnetic medium (the signal field). In SV sensors, the SV effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the free layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium causes a change in the direction of magnetization in the free layer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage.
FIG. 1
shows a simple SV sensor
100
comprising a pair of end regions
104
separated by a central region
102
. The central region
102
is formed by a suitable method such as sputtering onto a substrate
105
and has defined end regions that are contiguous with and abut the edges of the central region. A free layer (free ferromagnetic layer)
110
is separated from a pinned layer (pinned ferromagnetic layer)
120
by a non-magnetic, electrically-conducting spacer
112
. The magnetization of the pinned layer
114
is fixed through exchange coupling with an anti ferromagnetic (AFM) layer
116
.
A seed layer
109
, the free layer
110
, a spacer
112
the pinned layer
114
, the AFM layer
116
, and the cap layer
118
are all formed in the central region
102
. Hard bias layers
120
, formed in the end regions
104
, provide longitudinal bias for the free layer
110
. Leads
122
formed over the hard bias layers
120
provide electrical connections for the flow of the sensing current I
S
from a current source
124
to the MR sensor
100
. A sensing device
126
connected to the leads
122
senses the change in the resistance of the free layer
110
and the pinned layer
114
due to changes induced by an external magnetic field such as the field generated by a data bit stored on a disk drive media. IBM's U.S. Pat. No. 5,206,590 granted to Dieny et al. and incorporated herein by reference, discloses a GMR sensor operating on the basis of the SV effect.
One key to proper operation of a spin valve sensor is properly biasing the magnetization of the free layer so that the magnetization of the pinned and free layers are oriented in the manner shown in
FIG. 1
FIG. 2
shows the simple GMR spin valve sensor
100
of
FIG. 1
rotated 90 degrees. The spin valve sensor
100
of
FIG. 2
is shown with the air bearing surface at the bottom of the drawing (not shown). Seen in
FIG. 2
are various magnetic fields of a properly biased spin valve sensor
100
. The current I
S
passing through the sensor
100
is directed between the leads
106
(not shown) in a direction
125
coming out of the page. The magnetization M
P
from the pinned layer
114
is pinned through exchange coupling with the AFM in a direction
128
pointing down in the free layer
110
.
The magnetization M
P
of the pinned layer
114
induces a demagnetizing field H
D
through the free layer
110
with an orientation
132
pointing up. A field Hc also results from magnetic coupling between the pinned layer
114
and the free layer
110
. The magnetic coupling field Hc has a direction
134
going down in
FIG. 2. A
field His is induced within the free layer
110
as a result of the current I
S
and has a direction
130
acting downward through the free layer. As a result of the biasing through the cumulation of the fields in the sensor (including biasing from the hard bias layers
120
), the free layer
110
has a resultant magnetization M
F
oriented with a direction
130
acting perpendicular to the direction
128
of the magnetization M
P
of the pinned layer
114
. Preferably, the magnetization M
F
has a direction pointing either into or out of the page. In the depicted sensor
100
, the magnetization M
F
has a direction
130
pointing out of the page.
In this arrangement, where the magnetization M
F
in the free layer
110
and the magnetization M
P
in the pinned layer
114
are perpendicular to each other, the external magnetic field from the magnetized bits of the disk drive cause the magnetization M
F
to rotate (or “spin”) to a direction pointing either up or down depending on the value of the stored bit. For instance, an external magnetic field indicating a zero may have a direction causing the magnetization M
F
to rotate down to a direction parallel to the magnetization Mp, resulting in a low resistance condition in the sensor
100
. An external magnetic field indicating a one may have a direction causing the magnetization Mp to rotate up to a position antiparallel to the magnetization Mp, resulting in a high resistance condition in the sensor
100
.
When the magnetizations M
P
and M
F
are parallel, less electrons are scattered (ostensibly because only electrons with a spin in one direction are affected by the fields) and when the magnetizations M
P
and M
F
are antiparallel, more electrons are scattered (because electrons of both spin types are affected), causing a higher resistance condition. By monitoring these high and low resistance conditions, the applied external magnetic fields representing ones and zeroes on the disk drive media can be p
Kunzler & Associates
Tupper Robert S.
Watko Julie Anne
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