MICROSCOPIC THEORY OF MAGNETORESISTANCE IN GRANULAR-MATERIALS

Based on a simple model of spin-dependent scattering, an improved micr oscopic approach is proposed to describe the magnetoresistance in gran ular magnetic systems. The feature is the explicit account of correlat ed scattering of conduction electrons between granule pairs and of tra nsitions between spin-up and spin-down states. Besides the usual term, proportional to the square of the magnetization, an extra contributio n to the magnetoresistance ratio Delta rho/rho is obtained, proportion al to the correlator [cos theta(12)], where theta(12) is the angle bet ween magnetic moments of neighbor granules. The field dependence of De lta rho/rho, together with its dependencies on granule concentration, granule mean size, granule size distribution, temperature and annealin g effects, are considered, leading to a reasonable agreement with avai lable experimental data. [S0163-1829(98)02925-7].