Abstract: We have calculated the scattering cross sections of the magnetic granular films with small grains, each of which contains atom number n<12, and large grains (n>>12) by Born approximation. Besides, we derived the formulas of the giant magne-toresistances(GMR) of the films. The results show that for small grains the GMRincreases with the atom number n. At a scale n₀, the GMR has the maximum value. For n>n₀, GNR decreases with the number n. The results also show that GMR increases dis-tinctly with the roughness of the surface of the grains and it comes from the spin-depen-dent scattering between conduction electrons and magnetic grains. With our model, the calculation results are in agreement with the experiments reported.

Key words: giant magnetoresistance, magnetic granular film