Finite Size Effect in Cu-doped Ni thin Films

The finite size effect power law in Cu-doped Ni thin film were investigated by probing the Curie temperature (Tc)-dependence on the Ni(x)Cu(1-x)thin film thickness. It is found that both magnetization and Tc decreases proportional to the Cu content. Tc is directly proportional to the number of pairwise spin-spin interactions in a manifold cluster of spins according to the mean field approximation. The experiment results confirm the spin bag model built in ultrathin magnetic films previous, in which each spin interacts equally strongly with neighbors over some finite interaction length N-0. Furthermore, upon varying the composition of the Ni-Cu alloys, the range of spin-spin interactions N(0)decreases with increasing concentration of the Cu. Since there is little change of the band structure and conduct electron properties in Ni(x)Cu(1-x)alloy films, this phenomenon was attributed to the decreasing of the propagation distance of conduct electrons due to the scattering by the Cu impurities. The present results indicate the ferromagnetic order in 3d metal probably delivered by the itinerant electrons.