Field-induced anisotropy in the NiMn system with Pt impurities

Abstract

We have carried out ferromagnetic resonance (FMR) and magnetization measurements on Ni 76− x Mn 24Pt x ( x = 0, 1, 1.5, 2, 3) alloys. After cooling the samples down to 4.2 K in a magnetic field of 10 kG, the FMR and dc magnetization measurements have been done in the applied field either parallel (n-FC case) or antiparallel (r-FC case) to the cooling field direction for parallel geometry (static magnetization parallel to the surface of samples). It has been observed from the FMR and dc magnetization data that both the unidirectional and uniaxial anisotropies are significantly induced with increasing platinum impurity atoms. The ratio of the intensity of the resonance line for the r-FC case to that for the n-FC case increases with platinum as well. Furthermore, the line shapes are highly correlated with platinum. This asymmetric behaviour relative to the applied field direction has been discussed by taking into account the surface induced mode and introducing a directional character to the surface anisotropy in the Rado-Weertman (R-W) general surface boundary conditions.