Sputtering power dependence of the magnetic properties of CoCrPt

The magnetic properties of CoCrPt films produced by sputtering at power levels of 0.1, 0.3, 0.5, and 1 kW are studied with special emphasis placed on the structural properties we previously obtained using several x-ray experimental methods [J. Appl. Phys. 77, 2321 (1995)]. In measurements on the saturated magnetic state, the saturation magnetization of the 0.1 kW film was found to be about 20% lower than those of the other films. This is ascribed to the segregated structure of this film (described in the above reference). The out-of-plane magnetic anisotropy decreases as the sputtering power decreases. Its magnitude is related to the hcp(002) intensity and its orientation is slightly tilted from the normal direction. The in-plane magnetic anisotropy, on the other hand, increases sharply as the sputtering power decreases to levels below 0.5 kW. This increase is a result of the small grain structure produced by the sputtering at very low power levels. In the unsaturated magnetic state, three magnetic properties were measured: field-induced magnetic anisotropy and two types of magnetic torque loss, that is, intrinsic torque loss and field-induced torque loss related to field-induced magnetic anisotropy. The field-induced magnetic anisotropy is a consequence of the quenched magnetic domain structure produced by applying a strong external magnetic field. This anisotropy for films sputtered at 0.3, 0.5, and 1 kW is unusual in that the magnetization switching field is larger than the anisotropy field. This is ascribed to the intrinsic spatial and amplitude dispersion of the magnetization. Taking the structural and magnetic properties of CoCrPt into consideration made it clear that wall displacement rather than rotation magnetization is the major factor responsible for both types of torque loss. The rotation magnetization also made a significant contribution to intrinsic torque loss, but a limited contribution to field-induced torque loss.