Synthesis, characterization, and modeling of high quality ferromagnetic Cr-doped AlN thin films

Abstract

We report a theoretical and experimental investigation of Cr-doped AlN. Density functional calculations predict that the isolated $\mathrm{Cr}{\mathrm{ t}}_2$ defect level in AlN is 1/3 full, falls approximately at midgap, and broadens into an impurity band for concentrations over 5%. Substitutional ${\mathrm{Al}}_{\text{1−x}}{\mathrm{Cr}}_x\mathrm{N}$ random alloys with $\text{0.05⩽x⩽0.15}$ are predicted to have Curie temperatures over 600 K. Experimentally, we have characterized and optimized the molecular beam epitaxy thin film growth process, and observed room temperature ferromagnetism with a coercive field, $H_c,$ of 120 Oe. The measured magnetic susceptibility indicates that over 33% of the Cr is magnetically active at room temperature and 40% at low temperature.