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In this work, we report direct evidence of ferromagnetism in hydrogenated ZnO sub-micrometric powders. Hydrogen (H2) was incorporated under a high-pressure heat treatment in a sealed reactor. Ferromagnetism at room temperature can be activated and deactivated by annealing in H2 and air atmospheres, respectively. Hydrogen incorporation in ZnO structure was observed from X-ray absorption near-edge structure spectra where hydrogen acts as a shallow donor transferring electrons to the conduction band (Zn 4s). The Raman measurements evidence clear distortions in chemical environments of Zn atoms associated with defect formation. Our results suggest that magnetism is a superficial phenomenon probably related to the surface bonding of hydrogen to Zn (or O) on polar ZnO surfaces.

The structural, electronic, and magnetic properties of anatase TiO 2 samples 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 Ti 4+ ion, transfers charge to it, occupying unoccupied 3d levels. Longtime 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.

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