Ferromagnetism and Conductivity in Hydrogen Irradiated Co-Doped ZnO Thin Films.
Impressive changes in the transport and ferromagnetic properties of Co-doped ZnO thin films have been obtained by postgrowth hydrogen irradiation at temperatures of 400 °C. Hydrogen incorporation increases the saturation magnetization by one order of magnitude (up to ∼1.50 μB/Co) and increases the carrier density and mobility by about a factor of two. In addition to the magnetic characterization, the transport and structural properties of hydrogenated ZnO:Co have been investigated by Hall effect, local probe conductivity measurements, micro-Raman, and X-ray absorption spectroscopy. Particular care has been given to the detection of Co oxides and metal Co nanophases, whose influence on the increase in the transport and ferromagnetic properties can be excluded on the ground of the achieved results. The enhancement in ferromagnetism is directly related to the dose of H introduced in the samples. On the contrary, despite the shallow donor character of H atoms, the increase in carrier density n is not related to the H dose. These apparently contradictory effects of H are fully accounted for by a mechanism based on a theoretical model involving Co-VO (Co-O vacancy) pairs.
CNR-Istituto dei Sistemi Complessi, U.O.S. di Tor Vergata , Via del Fosso del Cavaliere 100, 00133 Roma, Italy.|Laboratori Nazionali di Frascati, INFN , Via E. Fermi 27, Frascati, RM 00044, Italy.
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Di Trolio
CNR-Istituto di Struttura della Materia, Via Salaria Km. 29,300, 00015 Monterotondo, Scalo, Italy.
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Alippi
CNR-Istituto di Struttura della Materia, Via Salaria Km. 29,300, 00015 Monterotondo, Scalo, Italy.
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Bauer
Synchrotron Soleil, L'Orme des merisiers, Saint-Aubin, BP48, 91192 Gif-sur Yvette, Cedex, France.
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Ciatto
Synchrotron Soleil, L'Orme des merisiers, Saint-Aubin, BP48, 91192 Gif-sur Yvette, Cedex, France.
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Chu
CNR-Istituto di Struttura della Materia, Via Salaria Km. 29,300, 00015 Monterotondo, Scalo, Italy.
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Varvaro
Dipartimento di Fisica, Sapienza Universitá di Roma , P.le A. Moro 2, 00185 Roma, Italy.
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Polimeni
Dipartimento di Fisica, Sapienza Universitá di Roma , P.le A. Moro 2, 00185 Roma, Italy.
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Capizzi
Dipartimento di Fisica, Sapienza Universitá di Roma , P.le A. Moro 2, 00185 Roma, Italy.|Casaccia Research Center, ENEA , via Anguillarese 301, 00060 Roma, Italy.
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Valentini
Dipartimento di Fisica, Universitá di Salerno , Via Giovanni Paolo II, Fisciano, SA 84084, Italy.
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Bobba
Dipartimento di Fisica, Universitá di Salerno , Via Giovanni Paolo II, Fisciano, SA 84084, Italy.
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Di Giorgio
CNR-Istituto di Struttura della Materia, Via Salaria Km. 29,300, 00015 Monterotondo, Scalo, Italy.
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Amore Bonapasta
Co-doped ZnO thin films; conductivity; ferromagnetism; hydrogen incorporation