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, ν_AF 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, J_k commonly became large and saturated with increasing ν_AF. The substantial coercivity originated from the AF layer decreased and became constant with increasing ν_AF. These experimental results were well explained by a simple model based on Meiklejohn's single spin model. We concluded that increasing ν_AF is key to induce the exchange anisotropy effectively in F/AF bilayers.