Systematic study of the exchange interactions in Gd-doped GaN containing N interstitials, O interstitials, or Ga vacancies

摘要

Using large supercells models and the KKRnano multiple scattering approach, statistically meaningful information is obtained on the distribution of local densities of states, magnetic moments, and distance-dependent exchange interactions for interstitial N or O or Ga vacancies in Gd-doped GaN. The exchange interactions between N interstitials (N_i) and N, with Gd are found to be short-ranged and mainly antiferromagnetic, while exchange interactions between Gd are negligible. For O interstitials, the ferro- and antiferromagnetic interactions between Gd and O_i are roughly canceling each other, and the O_i-O_i interactions are ferromagnetic but very short-ranged. The Fermi level dependence of these interactions is studied. The difference between N_i and O_i behavior is related to the filling of up and down spin partial densities of states, which promotes antiferromagnetic superexchange and ferromagnetic double exchange for N_i and O_i, respectively. On the other hand, Ga vacancies provide significantly stronger and more robust ferromagnetic interactions between moments localized on N near the vacancies and may reach the percolation threshold for concentrations of order 5%. The role of strain in films grown under different conditions on the vacancy concentration is discussed.