Effect of antiferromagnetic grain size on exchange anisotropy in Ni-Fe/25 at% Ni-Mn films

Abstract

The correlation between the antiferromagnetic (AF) grain volume, νAF and the exchange anisotropy is discussed for Ni-Fe/25 at% Ni-Mn system. In spite of various thickness combination of ferromagnetic (F) and AF layers, the unidirectional anisotropy constant, Jk commonly became large and saturated with increasing νAF. The substantial coercivity originated from the AF layer decreased and became constant with increasing νAF. These experimental results were well explained by a simple model based on Meiklejohn's single spin model. We concluded that increasing νAF is key to induce the exchange anisotropy effectively in F/AF bilayers.