Aluminum doping hexagonal barium ferrite films with large perpendicular magnetic anisotropy and high remanence ratio

Abstract

Aluminum doping hexagonal barium ferrite film with large perpendicular magnetic anisotropy (PMA) and high remanence ratio was prepared on Al2O3 substrate by post-annealing at high temperature. The crystal structure measurements have shown that the crystallinity and degree of orientation were improved by post-annealing at high temperature, while it happened the Al ions diffusion from the Al2O3 substrate into the ferrite film at 1100 °C of annealing temperature. The diffusion phenomenon is also confirmed by the distribution of elements in the cross-section which displays a wide and slow-changing region of Al element. The Al element diffusion gives rise to a decrease of saturation magnetization, and an increase of coercivity and remanence ratio. Generally, a hexagonal barium ferrite film with large PMA field (HA = 18.1 kOe), relatively small FMR linewidth (540 Oe) and high remanence ratio (86%) was obtained by annealing the film at 1100 °C, which shows potential applied in self-biased microwave devices.