GIANT MAGNETORESISTANCE IN MAGNETIC GRANULAR ALLOYS

Numerical simulation on resistance and giant magnetoresistance in magn etic granular alloys is performed for finite-size systems by making us e of the real-space Green's-function method based on the Kubo formalis m. Spin-dependent scattering causes the giant mapetoresistance in the magnetic granular alloys as in the magnetic multilayers. It is shown b y using the microscopic theory that the magnetoresistance increases wi th decreasing the size of magnetic grains, in agreement with experimen t. The theoretical results indicate that scattering at the surfaces of magnetic grains governs the resistance and mapetoresistance in granul ar alloys. Difference between the giant magnetoresistances in the gran ular alloys and multilayers is discussed.