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

Abstract

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 (Ni) and Ni with Gd are found to be shortranged and mainly antiferromagnetic, while exchange interactions between Gd are negligible. For O-interstitials, the ferro-and antiferromagnetic interactions between Gd and Oi are roughly cancelling each other, and the Oi-Oi interactions are ferromagnetic but very short-ranged. The Fermi level dependence of these interactions is studied. The difference between Ni and Oi behavior is related to the filling of up and down spin partial densities of states, which promotes antiferromagnetic super-exchange and ferromagnetic double exchange for Ni and Oi 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.

Magnetism of Eu-doped GaN modulations by spinodal nanodecomposition

“…45 Furthermore, Thiess et al proposed that the Ga vacancies provide significantly strong and robust ferromagnetic interactions between spins that are localized on the nitrogen near the vacancies. 46,47 Eu-doped GaN may also be affected by such native defects like Ga vacancies. We will focus on such effect in future studies.…”

Demonstration of defect-defect ferromagnetic coupling in Gd doped GaN epitaxial films: A polarization selective magneto-photoluminescence study

“…However, the microscopic origin of the defects and their involvement in establishing long range magnetic ordering is still unclear. Theoretical studies have shown that certain defects, such as Ga-vacancies(V Ga ), [15][16][17][18] 19 as well as nitrogen vacancy(V N )-Ga vacancy complexes 20,21 , which possess magnetic moment, can account for the large effective magnetic moment per Gd ion and explain ferromagnetism in this material. It is noteworthy that ferromagnetism above room temperature has been observed in semiconductors such as HfO, ZnO, TiO 2 , In 2 O 3 , where atoms with partially filled d or f shells are not present at all 22 .…”