Spin valve sensor

Details Spin valve sensor Spin valve sensor

2001-11-13

2004-03-09

Klimowicz, William (Department: 2652)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06704176

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to disc drive storage systems. More particularly, the present invention relates to spin valve sensors for use in disc drive storage systems.
BACKGROUND OF THE INVENTION
Disc drives are the primary devices employed for mass storage of computer programs and data used in computer systems. Disc drives typically use rigid discs, which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. A read/write head is adapted to read information from and write information to the data tracks.
The head is carried by a slider which is connected to an actuator mechanism through a gimbaled attachment. The actuator mechanism moves the slider from track-to-track across the surface of the disc under control of electronic circuitry. The actuator mechanism includes a suspension assembly that applies a load force to the slider to urge the slider toward the disc. As the disc rotates, air is dragged and compressed under bearing surfaces of the slider that create a hydrodynamic lifting force which counteracts the load force and causes the slider to lift and “fly” in close proximity to the disc surface. The gimbaled attachment between the slider and the suspension assembly allows the slider to pitch and roll as it follows the typography of the disc.
Giant magnetoresistive (GMR) sensors are used as read elements in read/write heads to read data recorded on the magnetic discs of the disc drive. The data are recorded as magnetic domains in the recording medium. As the data moves past an active region of the read element, the data causes changes in magnetic flux to the GMR sensor, which causes changes in the electrical impedance of the GMR sensor. A signal representing these impedance changes and, thus, the recorded data, is obtained by applying a bias or sense current through the sensor. Decoding circuitry is used to analyze the signal and retrieve the data. Typical read sensors utilizing the GMR effect, frequently referred to as “spin valve” sensors, are known in the art. These spin valve sensors are multi-layered structures consisting of two ferromagnetic (FM) layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the “pinned layer” because its magnetization is magnetically pinned or oriented in a fixed and unchanging direction by an adjacent anti-ferromagnetic (AFM) layer, commonly referred to as the “pinning layer,” through an anti-ferromagnetic exchange coupling. The other ferromagnetic layer is called the “free” or “unpinned” layer because its magnetization is allowed to rotate in response to the presence of external magnetic fields. The impedance of the spin valve varies as a function of the angle between the magnetization of the free layer and the magnetization of the pinned layer thereby producing the GMR effect. Contact layers are attached to the spin valve sensor to apply the sense current and obtain the signal from which the recorded data is obtained.
There is a never-ending demand for higher data storage capacity in disc drives. One measure of the data storage capacity is the areal density of the bits at which the disc drive is capable of reading and writing. The areal density is generally defined as the number of bits per unit length along a track (linear density and units of bits per inch) multiplied by the number of tracks available per unit length in the radial direction of the disc (track density in units of track per inch or TPI). Currently, there is a need for areal densities on the order of 100 Gb/in
2
which requires a track density on the order of 100-150 kTPI and greater.
One way to increase areal density of the data stored on a disc is to increase the track density by decreasing the track width and spacing between tracks. The smaller track widths and spacing require read elements with decreased active region widths and increased sensitivity to changing magnetic fields within the active region while avoiding side-reading. Side-reading occurs when a magnetic head responds to changing magnetic fields produced by adjacent tracks. This side-reading is a source of noise in the recovered data signal, and a source of cross-talk, a phenomenon where the read element reads data from two or more adjacent tracks. Consequently, the effects of side-reading in a read head is a limiting factor on the spacing between adjacent tracks, and hence a limiting factor to increased areal density.
The prior art teaches that in order for a GMR element to operate optimally, a longitudinal bias field should be applied to the free layer. The longitudinal bias field extends parallel to the surface of the recording media and parallel to the lengthwise direction of the GMR element. The function of the longitudinal bias field is to suppress Barkhausen noise which originates from multi-domain activities in the free layer of the GMR element. However, while it is important that the longitudinal bias field be strong enough to suppress the multi-domain activities in the free layer, it is also important for high areal density recordings that the longitudinal bias field be weak enough to allow the magnetization of the free layer to remain sensitive to external magnetic fields in the active region of the sensor.
Currently, two main longitudinal bias schemes for stabilization of the free layer are widely used. One scheme is based on the formation of a continuous free layer with end regions, which are longitudinally biased through an exchange coupling with adjoining anti-ferromagnetic patterns. The active region of the free layer is maintained in the desired single domain state due to the longitudinal bias field generated at the end regions of the free layer. In this scheme, the width of the active region of the free layer is primarily defined by the spacing of the conductor leads. Examples of such longitudinal bias schemes are described in U.S. Pat. Nos. 4,663,685 and 5,206,590. Although spin valve sensors with this type of longitudinal bias scheme exhibit satisfactory magnetic stability and sensitivity, they have relatively low track resolution due to side-reading at overlaid and regions of the free layer.
Another longitudinal biasing scheme is provided using permanent magnets which form abutted junctions to ends of the spin valve stack. In this scheme, the active region of the spin valve sensor is defined by the spacing between the abutted junctions. An example of a spin valve sensor using this longitudinal biasing scheme is described in U.S. Pat. No. 5,742,162 and is generally illustrated in FIG.
1
. The spin valve sensor
300
includes a sensor stack
302
that includes a ferromagnetic free layer
304
formed on an insulating layer
305
, and AFM layer
306
that pins a magnetization of ferromagnetic pinned layer
308
, and a conducting layer
310
. Permanent magnets
312
form abutted junctions to ends of the sensor stack and longitudinally bias the magnetization
314
in free layer
304
. A sense current
316
is delivered through the conducting layer
310
from conductor leads
318
which form abutted junctions to the ends of the spin valve stack
302
. The width of the active region of the spin valve sensor
300
is generally defined by the spacing between the permanent magnets
312
and the conductor leads
318
. The longitudinal bias field produced by the permanent magnets
312
is strong over the width of the active region resulting in enhanced track resolution but low sensitivity to external magnetic fields applied to the active region of the sensor.
It is known that the sensitivity of spin valve sensors having permanent magnets that form abutted junctions with the sensor stack can be enhanced by utilizing conductor leads that overlay the sensor stack as shown in the spin valve sensor
320
of FIG.
2
. Spin valve sensor
320
generally includes the same elements of sensor
300
of
FIG. 1
, but with the modification of permanent magnets
312
forming an abutted junction with the entire sensor stack
302
while conductor leads
318
overlay end regions o

Affiliated with

Also associated with

Rating

Spin valve sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Spin valve sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spin valve sensor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3272467