GaN films prepared on sapphire substrates with thickness of 30 pm, were implanted by nitrogen ions with energy of 80 keV at doses of 5 x 10(16) cm (2) and 2 x 10(17) 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 mu B in GaN crystal and form ferromagnetic coupling at room temperature between two close range Ga vacancies. (C) 2014 Elsevier B.V. All rights reserved.