Observation of Room-Temperature Ferromagnetism Induced by High-Pressure Hydrogenation of Anatase TiO2

Abstract

The structural, electronic, and magnetic properties of anatase TiO2samples annealed under different hydrogen pressures are reported. By combining X-ray photoelectron spectroscopy (XPS), Raman, UV-vis, and X-ray absorption near-edge structure (XANES) spectroscopies, evidence of hydrogen incorporation was detected in the anatase structure. Short-time high-pressure hydrogen treatment favors the production of interstitial hydrogen, which, located close to a Ti4+ion, transfers charge to it, occupying unoccupied 3d levels. Long-time hydrogenation treatments (10 h) help to rebuild the structure of anatase and heal defects, with hydrogen occupying mainly oxygen vacancies. The presence of reduced Ti(4−δ)+ions gives the sample its magnetic character at room temperature. Our results show that only a small fraction of the sample is magnetic (probably a superficial region affected by the hydrogenation) but the local magnetization is strong (in the order of hundreds of kA/m). By the choice of pressure and duration of treatment in a hydrogen atmosphere, it is possible to change the magnetic characteristics of the sample.