Magnetoresistance and exchange effects of NiCo/Cu sandwich films with oxide overlayer

Giant magnetoresistance (GMR) of 8% at 4.2 K is found in sandwich films having the composition Ni0.7Co0.3(50 Å)/Cu(t)/ NiCo(50 Å)/NiCoO(40 Å) where NiCoO is a mixed oxide overlayer that exchange couples with the NiCo alloy layer. These films show a MR temperature dependence quite similar to that previously reported for Co/Cu/Co/CoO where the MR becomes small above 200 K. When bilayers of CoO/NiO are placed on the NiCo layer, the temperature dependence of MR extends to 250 K. The magnitude of the MR at 4.2 K scales with the magnitude of the saturation magnetization in the NiCo and Co films.