Nitrogen vacancy and ferromagnetism in Cr-doped GaN: First-principles calculations

Abstract

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