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

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.Fil: Vázquez Robaina, Odin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Cabrera, Alejandra Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Fundora Cruz, Abel. Universidad de La Habana. Instituto de Ciencia y Tecnología de Materiales; CubaFil: RodrÍguez Torres, Claudia Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Room-Temperature Ferromagnetism Induced by High-Pressure Hydrogenation of ZnO

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.Fil: Vázquez Robaina, Odin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad de La Habana; CubaFil: Cabrera, Alejandra Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Meyer, Marcos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Romano, Rosana Mariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Fundora Cruz, Abel. Universidad de La Habana; CubaFil: RodrÍguez Torres, Claudia Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

TiN nanoparticles: small size-selected fabrication and their quantum size effect

Size-selected TiN nanoclusters in the range of 4 to 20 nm have been produced by an ionized cluster beam, which combines a glow-discharge sputtering with an inert gas condensation technique. With this method, by controlling the experimental conditions, it was possible to produce nanoparticles with a high control in size. The size distribution of TiN nanoparticles was determined before deposition by mass spectroscopy and confirmed by atomic force microscopy. The size distribution was also analyzed using a high-resolution transmission electron micrograph. The photoluminescence [PL] spectra of TiN nanoparticles at different sizes were also experimentally investigated. We reported, for the first time, the strong visible luminescence of TiN nanoparticles on Si (111) wafer due to the reduced size. We also discussed the PL intensity as a function of the nanoparticle size distribution