Spin-dependent CPP transport properties of semiconductive-oxide/ferromagnet multilayers

The spin-dependent CPP (current perpendicular to plane) transport properties in semiconductive-oxide(MO_x)/ferromagnet multilayers consisting of CoPt/Co/MO_x/Co/MO_x/Co/CoPt, where M = Ti, Sn, were investigated by magneto-transport measurement. The XRD patterns reveal that the structures of sputtered MO_x films are amorphous or nanocrystalline. The MR ratio of a TiO_x-based multilayer (0.43%) was much smaller than that of a SnO_x-based one (2.0%) at T = 77 K. As inferred from the shape of MR curves with a large saturation field above 4kOe, suppressed MR change in the TiO_x-based multilayer is caused by the interlayer diffusion of Co atoms into the TiO_x layer. The same behavior was not observed in the SnO_x-based one. The MR ratio was reduced by half on increasing t_SnO(x) from 4 to 8 nm. This decrease can be ascribed to the scattering of the spin-polarized electron in the SnO_x layer.