Influencing mechanisms of atomic diffusion and compositional distribution on the magnetic anisotropy of Cr/SmCo/(Cu)/Cr thin films

Abstract

Rare earth (RE) permanent magnetic thin films, such as SmCo-based films, are promising candidates for future thermal-assisted magnetic recording media because of their supreme thermal stability and fine superparamagnetic critical size. Phase compositional distributions and crystallographic orientations can directly influence the magnetic domain evolutions and magnetic performance of SmCo films. However, these films often exist in multi-phases without well-defined distinct magnetic anisotropy, thereby causing difficulties in analyzing their functions. The effects of atomic diffusions induced by annealing on crystallization and magnetic anisotropy energy are poorly understood. In this work, the influence of doping Cu atoms via introducing Cu layer on magnetic anisotropy of Cr/SmCo/(Cu)/Cr films is investigated. Introducing a Cu layer and post-annealing lead to tunable magnetic anisotropy from isotropy to anisotropy and domain structure formation. Micromagnetic simulation is used to further analyze the effects of crystallization, anisotropy field and compositional distribution on the magnetization reversal behavior and coercivity variations in SmCo films. It reveals that the differences of anisotropy field of Co and amorphous phases could affect the domain wall motions and coercivity, which shows the analogous trend as an experimental result. Moreover, the elevated anisotropy constant of Sm(Co,Cu) alloy and the small fractions of SmCo5 boundary phases are also beneficial to the enhancement of coercivity derived by calculating domain wall energy. In-plane magnetic anisotropy is improved by the SmCo5 phase, which has an in-plane preferred orientation of the c axis. This work provides theoretical and experimental bases for the future fabrication of SmCo-based films by controlling atomic diffusion with optimized grain boundary phase distribution.