Synthesis by ball milling and characterization of nanocrystalline Fe3O4 and Fe/Fe3O4 composite system

Nanocrystalline Fe3O4 and a composite system constituted by nanocrystalline Fe and Fe3O4 have been synthesized by ball milling commercial magnetite an d an equimolar mixture of iron and magnetite powders. The physical paramete rs governing the milling process have been strictly controlled so as to ach ieve the nanocrystalline state of the precursor material and to avoid chemi cal reactions. X-ray diffraction and Mossbauer spectroscopy measurements ha ve been carried out both on as-milled powders and on samples previously sub jected to annealing treatments in the 100-600 degreesC temperature range. T he results, providing information on the structural and compositional featu res of the produced samples, are discussed in terms of structural disorder which is healed by subsequent annealing. In the case of the composite syste m, this analysis indicates that a high mixing degree between the constituen t phases has been reached. In particular, the presence of a sextet with ano malous hyperfine parameters in the Mossbauer spectrum of as-milled Fe+Fe3O4 has been associated with an alteration of the magnetite structure at the i nterface with bcc Fe. For both sets of samples, the influence of the struct ural features on the macroscopic magnetic behavior has been investigated by performing magnetic hysteresis loop measurements at room temperature. (C) 2001 American Institute of Physics.