Recently there has been great interest in the transport properties of layered magnetic materials because of the discovery of a new form of magnetoresistance~1 called the giant magnetoresistance (GMR). GMR is a change in the electrical resistivity of a magnetically inhomogeneous material that occurs when the application of a magnetic field brings the moments in different regions into alignment. GMR has been observed in several geometries, but the most promising and interesting GMR systems are composed of thin layers of ferromagnetic material separated by non-magnetic or very weakly magnetic spacer layers. For layered GMR systems, leectric fields are usually applied so that the current flows parallel to the layers. This "current in the plane" geoemtry will be assumed in this paper.
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