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Autori: Ovidiu Crisan, Jean-Marc Greneche, Ivan Skorvanek, Radu Nicula, Eberhard Burkel, George Filoti
Editorial: Institute of Physics Publishing, Journal of Physics D: Applied Physics, p.submitted, 2007.
Systems composed of ferromagnetic – antiferromagnetic phases that exhibit exchange bias properties are of great importance for technological applications. We report a structural and magnetic study of nanopowders obtained by ball milling of a mixture of Fe and Fe3O4 at room temperature. Temperature-dependent X-ray diffraction studies show formation of wüstite (FeO) via an incomplete redox reaction during the milling. Wüstite co-exists in the as-milled state with magnetite and -Fe. With increasing temperature, the relative proportion of FeO decreases and -Fe and Fe3O4 are formed again. Magnetic measurements show the occurrence of a significant exchange bias effect in the as-milled state, effect that gradually decreases upon annealing the samples, probably due to the vanishing of the FeO. The magnetic behavior is correlated to the observed microstructure made of mixed metal / Fe oxides phases. The occurrence of exchange bias effects is discussed and related to the samples microstructural features
Cuvinte cheie: magnetic nanopowders; exchange bias; ball milling; FM/AFM systems; X-ray diffraction;