Magnetic after-effect in amorphous Tb–Fe thin films

Magnetic after-effect in sputter deposited Tb_xFe_1−x (x×0.17∼0.24) films is studied. The after-effect is directly observed using polar Kerr magneto-optic effect as a slow propagation of domain walls. The velocity of the domain growth (10⁻⁴∼10⁻¹ cm/s) changes exponentially with the applied field. The viscosity coefficient S_v≡dM/d ln t·χ⁻¹ (χ: irreversible susceptibility), which was used in describing Jordan type after-effect, is applied to characterize the after-effect. The value of S_v (22∼110 Oe) is inversely proportional to the saturation magnetization at room temperature and decreases with rising temperature. The origin of the slow wall motion is inferred to be the random anisotropy of Tb ion rather than the oxidation of the film surface.