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Compensation During Use for the Magnetic Annealing of a Magnetoresistive Sensor

IP.com Disclosure Number: IPCOM000101319D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Gurney, BA: AUTHOR

Abstract

A method to continuously compensate for the effects of use-related magnetic annealing of the magnetoresistive (MR) material in an MR sensor is disclosed. It uses an adjacent conductive bias layer (BL) that is electrically isolated from the MR material to provide a bias magnetic field to rotate the MR magnetization (M) to the angle where optimal sensing occurs. As the MR material anneals, its easy axis and anisotropy field change, but by varying the current through the bias layer the optimal signal symmetry can be continuously maintained.

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Compensation During Use for the Magnetic Annealing of a Magnetoresistive Sensor

       A method to continuously compensate for the effects of
use-related magnetic annealing of the magnetoresistive (MR) material
in an MR sensor is disclosed.  It uses an adjacent conductive bias
layer (BL) that is electrically isolated from the MR material to
provide a bias magnetic field to rotate the MR magnetization (M) to
the angle where optimal sensing occurs.  As the MR material anneals,
its easy axis and anisotropy field change, but by varying the current
through the bias layer the optimal signal symmetry can be
continuously maintained.

      A number of MR sensor designs require that M be rotated away
from the easy axis during sensing in order to enhance signal
magnitude and linearity.  This places the MR film out of equilibrium
and, under these conditions, relaxation processes are known to occur
in commonly used MR materials, often resulting in a rotation of the
easy axis and reduction of the anistropy field (1). In designs where
M is returned to the easy axis when sensing is not being performed,
there should be some annealing back to the desired film properties
(2). However, the elevated temperature that accompanies the flow of
sense current during the sensing process means that more annealing
effects may occur during sensing than can be removed by extended idle
times with M returned to the easy axis.  Over the lifetime of the
sensor, annealing effects are expected to result in asymmetry and
signal loss.  A conceivable solution is to use an MR material that
does not exhibit annealing effects over the expected devic...