Dependence of the giant magnetoresistance on the concentration of magneticparticles in granular composites

We study the dependence of giant magnetoresistance (GMR) on the volume conc entration of magnetic particles in a magnetic granular composite via a Mont e Carlo method and by modeling the composite as a random resistor network. We assume the nanosized magnetic particles are spherical in shape and are r andomly distributed in a square or cubic lattice. The uniaxial anisotropy o f the particles and the classical dipolar interaction among the particles a re taken into account. By considering the difference in electron scattering s for spin-up and spin-down conduction electrons at the magnetic and nonmag netic interface, and the scatterings within the magnetic regions and the no nmagnetic host medium in the composite, the value of GMR is found to depend sensitively on the spatial distribution of the particles, the magnetic sta tes of the particles, and the densities of the spin polarized conduction el ectrons. There is an optimum concentration (about 25% in two-dimensional an d 30% in three-dimensional cases) of magnetic particles at which the magnet oresistance shows a maximum. This phenomenon was also observed in experimen ts. (C) 2001 American Institute of Physics.