  High Curie temperature of 900 K has been reported in Cr-doped AlN diluted
magnetic semiconductors prepared by various methods, which is exciting for
spintronic applications. It is believed that N defects play important roles in
achieving the high temperature ferromagnetism in good samples. Motivated by
these experimental advances, we use a full-potential density-functional-theory
method and supercell approach to investigate N defects and their effects on
ferromagnetism of (Al,Cr)N with N vacancies (V_N). Calculated results are in
agreement with experimental observations and facts of real Cr-doped AlN samples
and their synthesis. Our first-principles results are useful to elucidating the
mechanism for the ferromagnetism and exploring high-performance Cr-doped AlN
diluted magnetic semiconductors.
