PHENOMENOLOGICAL THEORY OF THE GIANT MAGNETORESISTANCE OF FERROMAGNET-NONMAGNETIC METAL GRANULAR MEDIA

A phenomenological model is developed for the giant magnetoresistance of granular media comprising ferromagnetic granules in a nonmagnetic m etal matrix. Both volume and surface spin-dependent scattering by the ferromagnetic granules are taken into account. The internal electric f ields are inhomogeneous because of the different conductivities of the granules and the matrix. The dependence of the effective conductivity of the medium on the average magnetization is calculated and used to explain the giant magnetoresistance effect. The magnetoresistance is p lotted as a function of the volume concentration of ferromagnetic gran ules and the granule radius. Experiments on Co-Cu and Co-Ag granular f ilms are discussed. (C) 1998 American Institute of Physics. [S1063-783 4(98)02110-8].