High-Temperature Mössbauer Spectroscopy of Mechanically Milled NiFe2O4

Oxide spinels, in particular those containing iron, often exhibit technically important electrical- and magnetic-properties. We report here on X-ray powder diffraction and Mössbauer studies of nanostructured NiFe₂O₄ particles prepared by high-energy ball milling from bulk NiFe₂O₄, which is an inverse spinel. The Mössbauer spectra were recorded in situ at different temperatures in the range of 300–850 K. The Mössbauer spectra of the milled samples show a broad distribution of magnetic hyperfine fields together with a paramagnetic state at room temperature. Initially, at 700 K the spectrum is mainly paramagnetic, but during the process of annealing, magnetic sextets emerge. The treatment results in a significant change in the B/A area ratio of the ferrite. The Neél temperature of the samples is estimated from the B(T) relation to be in the range of 800–850 K.