Room temperature ferromagnetism in N-implanted MgO: synergistic effects of intrinsic and extrinsic defects

N-implanted MgO single crystals were prepared and their magnetic properties were studied. High Resolution x-ray diffraction, photoluminescence, and x-ray photoelectron spectroscopy measurements confirmed that both intrinsic defects (Mg vacancies, oxygen vacancies) and extrinsic defects (N-related defects) were presented in the implanted samples. Ferromagnetism was detected in the samples. The saturation magnetization (Ms) of the samples increases with the concentrations of Mg vacancies and N-related defects. We conclude that the enhanced Ms should be ascribed to the synergistic effects of intrinsic and extrinsic defects. The magnetic properties of various composite defects were also studied by first principle calculations. The results suggest that the ferromagnetism is mainly originated from the configurations of V_Mg (Mg vacancy)+N_O (N substituting for O). (paper)