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Improved Magnetoresistive Sensor

IP.com Disclosure Number: IPCOM000116225D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Gambino, RJ: AUTHOR [+2]

Abstract

In granular magnetic materials used in MagnetoResistive (MR) sensors the MR figure of merit, Delta rho divslash rho (where &rho. is the sensor resistivity in zero magnetic field and Delta rho is the change in resistivity with magnetization), depends critically on annealing conditions, e.g., time and temperature. The field dependence of the magnetization is also dependent on annealing conditions. For sensor applications, such as MR read heads for magnetic recording, the largest change in resistivity per unit magnetic field is needed. The problem is to anneal the granular material in a way which optimizes the MR properties.

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Improved Magnetoresistive Sensor

      In granular magnetic materials used in MagnetoResistive (MR)
sensors the MR figure of merit, Delta rho divslash rho (where &rho.
is
the sensor resistivity in zero magnetic field and Delta rho is the
change in resistivity with magnetization), depends critically on
annealing conditions, e.g., time and temperature.  The field
dependence
of the magnetization is also dependent on annealing conditions.  For
sensor applications, such as MR read heads for magnetic recording,
the
largest change in resistivity per unit magnetic field is needed.  The
problem is to anneal the granular material in a way which optimizes
the MR properties.

      In granular MR sensors a magnetic metal, such as Co, is
precipitated out of a conductive matrix such as Cu.  The MR effect is
associated with scattering of the charge carriers at the interface
between the ferromagnetic metal and the matrix so it is important to
have a large interfacial surface area.  According to the theory [1]
Delta rho divslash rho is inversely proportional to the particle
radius.  On the other hand, when the particles are too small they
become superparamagnetic and are therefore difficult to saturate.
For high field sensitivity it is essential that the MR sensor be easy
to saturate.  The field dependence of the MR effect comes about
through the field dependence of the magnetization.  According to
Zhang Delta rho divslash rho is proportional to lbrc 1 %% mdash %%
(M(H) divslash M sub s) sup 2 rbrc where M sub s is the saturation
magnetization and M(H) is the magnetization at filed H.

      The resistivity in zero field is strongly dependent on the
fraction of the magnetic metal in solid solution.  For example, an
alloy film of Cu with 8.3%Co has a resistivity of 28 mu Omega cm in
the as deposited condition and 7 mu Omega cm after a long anneal at
400 degrees C.  From the saturation magnetization we know that the
long
anneal was sufficient to precipitate essentially all the Co where as
in the as deposited state only about 60% of the Co is precipitated,
the remainder is in solid solution in the Cu matrix.  Therefore, the
resistivity can be used to monitor the precipitation process.

      The precipitation process in...