Nitrogen defects and their effect upon the ferromagnetism of Cr-doped GaN were systematically investigated using first principles. The four considered configurations, including one N vacancy (VN), single substitutional Cr, double substitutional Cr and a Cr–VN complex, 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 a 5.998μB moment (more than twice the moment of one Cr) via strong d–d spin coupling, which was mediated by two Cr 3d states antiferromagnetically coupling with so-called 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 reduced the ferromagnetic spin exchange interaction between the nearest Cr–Cr pairs. Thus, experimentally, high-performance samples might be synthesized by controlling the 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