Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-04-03
2004-11-30
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06826021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to magnetic heads, and more particular to antiparallel (AP) pinned type spin valve (SV) sensors having ultra-thin freelayers.
2. Description of the Related Art
Computers often include 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 re 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 in the MR element and the direction of sense current flow 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 is the giant magnetoresistance (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 only two layers of ferromagnetic material (e.g., Ni—Fe) separated by a layer of non-magnetic material (e.g., Cu) are generally referred to as spin valve (SV) sensors manifesting the GMR effect (also referred to as the SV 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 freelayer, however, is not fixed and is free to rotate in response to the field from the recorded magnetic medium (the signal field). In the SV sensor, the SV effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the freelayer. 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 direction of magnetization in the freelayer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage. IBM's U.S. Pat. No. 5,206,590 granted to Dieny et al. and incorporated herein by reference, discloses an MR sensor operating on the basis of the SV effect.
FIG. 1
shows a prior art SV sensor
100
comprising end regions
104
and
106
separated from each other by a central region
102
. A freelayer (free ferromagnetic layer)
110
is separated from a pinned layer (pinned ferromagnetic layer)
120
by a non-magnetic, electrically-conducting spacer
115
. The magnetization of the pinned layer
120
is fixed by an antiferromagnetic (AFM) layer
125
. Freelayer
110
, spacer
115
, pinned layer
120
and the AFM layer
125
are all formed in the central region
102
over a substrate
128
. Hard bias layers
130
and
135
formed in the end regions
104
and
106
, respectively, provide longitudinal bias for the freelayer
110
. Leads
140
and
145
formed over hard bias layers
130
and
135
, respectively, provide electrical connections for the flow of the sensing current I
s
from a current source
160
to the MR sensor
100
. Sensing means (a detector)
170
connected to leads
140
and
145
senses (detects) the change in the resistance due to changes induced in the freelayer
110
by the external magnetic field (e.g., field generated by a data bit stored on a disk).
Another type of SV sensor is an antiparallel (AP) pinned SV sensor. In AP-pinned SV sensors, the pinned layer is a laminated structure of two ferromagnetic layers separated by a non-magnetic coupling layer such that the magnetizations of the two ferromagnetic layers are strongly coupled together antiferromagnetically in an antiparallel orientation. The AP-pinning method provides improved pinning for the ferromagnetic layer than is achieved with the pinned layer structure of the SV sensor of FIG.
1
. This improved pinning increases the stability of the AP-Pinned SV sensor at high temperatures and enhances its performance in hard disk drives.
FIG. 2
shows a prior art AP-pinned SV sensor
200
comprising end regions
204
and
206
separated from each other by a central region
202
. A freelayer
210
is separated from a laminated AP-pinned layer structure
220
by a nonmagnetic, electrically-conducting spacer layer
215
. The magnetization of the laminated AP-pinned layer structure
220
is fixed by an antiferromagnetic (AFM) layer
230
. The laminated AP-pinned layer structure
220
comprises a first ferromagnetic layer
222
and a second ferromagnetic layer
226
separated by an antiparallel coupling (APC) layer
224
of nonmagnetic material. The two ferromagnetic layers
222
,
226
(PF
1
and PF
2
) in the laminated AP-pinned layer structure
220
have their magnetization directions oriented antiparallel, as indicated by the arrows
223
,
227
(arrows pointing into and out of the plane of the paper respectively). The AFM layer
230
is formed on a seed layer
240
deposited on the substrate
250
. To complete the central region
202
of the SV sensor, a capping layer
205
is formed on the freelayer
210
. Hard bias layers
252
and
254
formed in the end regions
204
and
206
, respectively, provide longitudinal bias for the freelayer
210
. Leads
260
,
265
provide electrical connections for the flow of the sensing current I
s
from a current source
270
to the SV sensor
200
. Sensing means
280
connected to leads
260
,
265
senses the change in the resistance due to changes induced in the freelayer
210
by the external magnetic field (e.g., field generated by a data bit stored on a disk).
FIG. 3
is a more detailed depiction of a read head
300
having a spin valve (SV) sensor
302
of the AP-pinned type, which is described in U.S. Pat. No. 6,317,299 B1. This SV sensor
302
is generally formed over a first read gap layer
301
. SV sensor
302
includes a nonmagnetic conductive spacer layer (S)
304
which is located between a freelayer structure
306
and an AP-pinned layer structure
352
. Freelayer structure
306
includes freelayers (F)
314
and a nanolayer (NL)
316
with the nanolayer located between spacer layer
304
and freelayers
314
for increasing the magnetoresistive coefficient (dR/R) of SV sensor
302
.
Freelayer structure
306
has a magnetic moment
318
which is directed parallel to the ABS from left to right as shown, or optionally from right to left. Magnetic moment
318
is rotated upwardly and downwardly by signal fields from the rotating magnetic disk. When the sense current (I
s
) is conducted through SV sensor
302
a rotation of magnetic moment
318
upwardly increases the resistance of the sensor and a rotation of magnetic moment
318
downwardly decreases the resistance which are processed as playback signal
Oskorep, Esq. John J.
Renner Craig A.
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