Intrinsic ferromagnetism due to cation vacancies in Gd-doped GaN: First-principles calculations

We report total-energy electronic-structure calculations based on density-functional theory that clarify magnetism of Gd-doped GaN. We find that Ga vacancies with the magnetic moment of $3{\mu }_B$ formed upon Gd doping interact ferromagnetically with each other and thus cause gigantic magnetic moments per Gd atom. Our detailed analyses are indicative of intrinsic ferromagnetism due to cation vacancies rather than magnetic dopants in nitride semiconductors.

Figure 1

(Color online) (a) Optimized atomic structure of GaN:Gd with two Ga vacancies using the 96-site wurtzite supercell. (b) Density of states for the most stable electronic structure of the atomic configuration shown in (a) which is ferromagnetic. The local density of states for Gd and its $f$ component are also shown. Majority and minority spins are denoted as “up” and “down,” respectively.

Figure 2

(Color online) Magnetic moment per Gd atom with respect to the number of $V_{\text{Ga}}$.

Figure 3

(Color online) Total energies of various spin configurations for ten $V_{\text{Ga}}$ in ${\text{Gd}}_{0.02}{\text{Ga}}_{0.98}\text{N}$ as a function of the magnetic moment per Gd atom. Energies are relative to that of the most stable ferromagnetic configuration. The long arrows represent the spin of Gd schematically, whereas the short ones are for Ga vacancies.