Oxygen vacancy enhanced room temperature ferromagnetism in Ar+ ion irradiated WO3 films

Room-temperature ferromagnetism in WO3 films was enhanced by 130 keV Ar+ ion irradiation. The X-ray diffraction (XRD) and Raman measurements not only confirmed the monoclinic phase of the irradiated WO3 films, but also showed that oxygen vacancy (V-o) defects were formed. The analysis of photoluminescence spectra strongly reconfirmed the presence of oxygen vacancy. X-ray photoelectron spectroscopy (XPS) measurements revealed that the contents of V-o and induced W5+ ions increase with increasing irradiation fluence and rich W5+ V-o defect complexes in the irradiated WO3 films were formed. Further, the magnetic measurements exhibited a 2-fold enhancement in the saturation magnetization at the largest fluence of 3 x 10(16) ions/cm(2). At lower irradiation fluence, a bound magnetic polamn model was proposed to reveal the ferromagnetic exchange coupling resulting from overlapping of V-o(+) and V-o(++) defect states, and 5d(1) states of W5+. At high irradiation fluence, the carrier concentration reaches 1.02 x 10(20)/cm(3) and carrier-mediated exchange interactions result in the film's ferromagnetism.