Nitrogen defects and their effect on the ferromagnetism in Cr-doped GaN were systematically investigated by first-principles. Four considered configurations including one N vacancy (VN), single substitutional Cr, double substitutional Cr, and complex of Cr–VN were all ferromagnetic. The lowest energy arrangements for double Cr-doped (or Cr–VN) GaN occurred at the nearest Cr–Cr (or Cr–VN) distance. One Cr contributed 84.3% of the total magnetic moment (2.533μB), while one Cr–Cr pair led to 5.998μB moment (more than twice moment of one Cr) by the strong d–d spin coupling, which was mediated by two Cr 3d states antiferromagnetically coupling with the “commonly shared” N 2p states, and driven by a double exchange mechanism. The VN could enhance the ferromagnetism by adding about 1μB to the Cr moment but reduce the ferromagnetic spin exchange interaction between the nearest Cr–Cr pairs, so experimentally, high-performance samples might be synthesized by controlling N pressure.

Nitrogen Vacancy and Ferromagnetism in Cr-Doped GaN: First-Principles Calculations. Y.Li, W.Fan, H.Sun, X.Cheng, P.Li, X.Zhao, M.Jiang: Journal of Solid State Chemistry, 2010, 183[11], 2662-8