Mechanism of RIS in Thin Magnetic Films

Two models, model 1 and model 2, which lead to type 1 and type 2 RIS (rotatable initial susceptibility), respectively, are presented. In model 1, the film is considered to be composed of many crystallites with a uniaxial anisotropy, whose easy axis is randomly oriented within the plane of the film. The magnetization of each crystallite is thought to be coupled with each other through an effective field which is parallel and proportional to the mean magnetization of the film. In model 2, anisotropy centers with the same uniaxial anistropy are distributed in the completely isotropic medium, with their easy axes randomly oriented within the plane of the film. The postulated interaction, in this case, is the one between the anisotropy centers and the isotropic medium only. In this case also, the interaction is thought to be caused through an effective field acting on the anisotropy centers from the isotropic medium, which is parallel and proportional to the magnetization of the isotropic medium whose local magnetizations are always kept parallel with each other. For these two models, critical curves of the external field for irreversible rotation of the mean magnetization, according to which the characteristics of both type 1 and type 2 RIS are derived, have been obtained by numerical calculations.