Giant magnetoresistance and magnetic anisotropy of Co₉Fe/Cu/Co₉Fe multilayer thin films on an MgO(110) substrate

Magnetoresistive effects have been investigated using Co₉Fe/Cu/Co₉Fe that were deposited on an MgO(110) substrate by ion beam sputtering with a 21‐A‐thick CU layer and with various thicknesses of the Co₉Fe films. The influence of a 50‐A‐thick Fe buffer layer has also been investigated. In addition to a cubic symmetry anisotropy (K₁), an in‐plane uniaxial magnetic anisotropy (K_u) was induced, which easy axis is parallel to the (110) plane of the MgO substrate and the (001) plane with and without the 50‐A‐thick Fe buffer layer, respectively. The magnetoresistance (MR) ratio decreased monotonically with increasing thickness of the Co₉Fe films from 25 A to 70 A. A maximum MR ratio of 11.5 percent was obtained at room temperature. With increasing magnetic field, the MR ratio reached a plateau gradually after a steep drop at small magnetic fields without the Fe buffer layer. It reached a plateau rapidly at small magnetic fields with the Fe buffer layer. By considering both K_u and K₁, these behaviors can be accounted for by the magnetization processes involved.