GIANT NEGATIVE MAGNETORESISTANCE IN GRANULAR FERROMAGNETIC SYSTEMS

Giant negative magnetoresistance (GMR) has been observed in a number o f granular ferromagnetic systems [Co-Ag, Co-Cu, Fe-Cu, Fe-Ag, and (Fe- Ni) Ag] with effect sizes as much as 85% at 5 K and 25% at 300 K. It i s shown that the GMR is isotropic and is due to magnetic scattering of the conduction electrons by the nonaligned magnetic entities. The ess ential contribution to the resistivity is rho(m)[1-F(M/M(s))], where F (M/M(s)) measures the spin disorder from ferromagnetic alignment and r ho(m) is the magnetic resistivity that defines the size of the GMR. Th e magnitude of GMR is affected by the size and density of the magnetic entities which can be controlled by varying the composition and the p rocess conditions. When the composition is varied, the maximum GMR is realized in systems with magnetic constituents of about 25%.