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 and an equimolar mixture of iron and magnetite powders. The physical parameters governing the milling process have been strictly controlled so as to achieve the nanocrystalline state of the precursor material and to avoid chemical reactions. X-ray diffraction and Mössbauer spectroscopy measurements have been carried out both on as-milled powders and on samples previously subjected to annealing treatments in the 100–600 °C temperature range. The results, providing information on the structural and compositional features of the produced samples, are discussed in terms of structural disorder which is healed by subsequent annealing. In the case of the composite system, this analysis indicates that a high mixing degree between the constituent phases has been reached. In particular, the presence of a sextet with anomalous hyperfine parameters in the Mössbauer spectrum of as-milled Fe+Fe3O4 has been associated with an alteration of the magnetite structure at the interface with bcc Fe. For both sets of samples, the influence of the structural features on the macroscopic magnetic behavior has been investigated by performing magnetic hysteresis loop measurements at room temperature.