Inducing high coercivity and anisotropy into strained Fe-Co thin films, towards rare earth free permanent magnets applications

Abstract

The present study is focused on our effort towards high performance permanent magnets with no rare earth elements. For this reason, high magnetization FeCo system is proposed as an alternative candidate. High magneto-crystalline anisotropy along with high magnetic moment is required for permanent magnets. According to theoretical calculations FeCo alloy can support large uniaxial magnetic anisotropy energy (MAE), Ku and saturation magnetization Ms [1], while tetragonal distortion can be induced via coherent growth of Fe-Co layers on different substrate or buffer materials. Based on a combinatorial exploration of AuCu underlayer lattice constant [2] we employed AuCu as a buffer layer in our system. Adding a third element, e.g. Carbon, was recently proposed to stabilize the strain in Fe-Co, preventing the complete lattice relaxation of the system [3], while an increased magnetocrystalline anisotropy was observed in FeCoC thin films [4]. We report giant perpendicular anisotropy in our thin magnetic films in the excess of 1MJ/m3, confirmed by FMR measurements and coercivity induction of almost 850Oe in our multilayers films approach.