THEORY OF GIANT MAGNETORESISTANCE FOR PARALLEL AND PERPENDICULAR CURRENTS IN MAGNETIC MULTILAYERS

For a magnetic multilayer system, the physical origin of the difference between the giant magnetoresistances for currents parallel and perpendicular to the layer planes is studied. In order to take into account the two characteristics of a multilayer system, interfacial roughness and layered structure, we adopt the single-cell coherent-potential approximation. The spin-dependent resistivities are calculated for currents parallel and perpendicular to the layer planes by using a single-band tight-binding model and the Kubo formalism. It is shown that the magnetoresistance ratio for perpendicular current is larger than that for parallel current. The difference between magnetoresistances for parallel and perpendicular currents is attributed to the fact that the effects of the anisotropy of the effective mass and the two-dimensional distribution of randomness on the anisotropy of the resistivity depend on the spin-dependent potential. It is also shown that interfacial roughness is favorable to magnetoresistance for parallel currents. © 1995 The American Physical Society.