A unified theory of CIP and CPP giant magnetoresistance in magnetic sandwiches

A theory of giant magnetoresistance (GMR) in magnetic sandwiches F/P/F for current in plane (CIP) and current perpendicular to plane (CPP) geometries is developed. We adopted the free electron model described by four parameters: mean free paths and scattering amplitudes (coherent potentials) at the interfaces for spin-up and spin-down electrons. For both CIP and CPP geometries, we calculated the conductivities and GMR using Kubo formalism and the Green function technique in mixed real space-momentum representation. The final expressions for GMR in both geometries were obtained using the same microscopic parameters. Main attention was paid to the relative role of spin-dependent bulk and interfacial scattering. It was shown that increasing of surface scattering for fixed spin asymmetry leads to non-monotonic behaviour of CIP GMR due to renormalization of the scattering amplitude. In the case of CPP geometry the dependence of GMR on interfacial scattering amplitude is monotonic.