Rise And Fall Of Ferromagnetism In O-Irradiated Al2o3 Single Crystals

In dilute magnetic semiconductors studies, sapphire was usually used as non-magnetic substrate for films. We observed weak ferromagnetic component in Al2O3 single crystal substrate, and excluded the possibility of ferromagnetic contaminations carefully by inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy. The ferromagnetism rise and fall during the process of annealing-oxygen irradiation-annealing of the sapphire. The ferromagnetic changes are consistent with Al-vacancy related defects detected by positron annihilation spectroscopy. With first-principle calculations, we confirm that Al-vacancy can introduce magnetic moment for 3 mu B in Al2O3 crystal and form stable V-Al-V-Al ferromagnetic coupling at room temperature. (C) 2015 AIP Publishing LLC.