Ga-vacancy induced room temperature ferromagnetism observed in N-irradiated GaN films

GaN films prepared on sapphire substrates with thickness of 30 μm, were implanted by nitrogen ions with energy of 80 keV at doses of 5 × 1016 cm−2 and 2 × 1017 cm−2, respectively. An obvious ferromagnetic loop was obtained in the higher dose irradiated GaN film at room temperature, indicating magnetic defects were induced into this film. After irradiation, the films contained lots of Ga vacancies were investigated by slow positron annihilation spectroscopy. With first-principle calculations, we demonstrated that Ga vacancies could lead to an enhancement of magnetic moment for 3 μB in GaN crystal and form ferromagnetic coupling at room temperature between two close range Ga vacancies.