Demagnetization process and hysteresis loops in perpendicularly oriented hard/soft trilayers

Abstract

Nucleation and evolution of domain walls as well as the magnetic reversal process in perpendicularly oriented hard/soft trilayers have been investigated within a micromagnetic approach, concentrated on the situation with very thin hard layer. The formula for the nucleation field has been derived, which falls as the soft layer thickness rises. Negative nucleation field occurs at thick soft layer when the shape anisotropy surpasses the crystalline one, where the magnetization in the center of the soft layer obeys the coherent rotation model. The microscopic and macroscopic hysteresis loops have been calculated numerically, with the angular distribution of the magnetization between the nucleation and pinning fields obtained. The area of the hysteresis loop decreases while the coercivity mechanism changes from nucleation to pinning as the soft layer thickness increases. The effect of the hard layer thickness is contrary to that of the soft layer, however, the former affects the demagnetization process and hysteresis loops significantly only when the layers are thin enough.