Anomalous change in electron density at nuclear sites in nanosize zinc ferrite

Nanosize samples of zinc ferrite with different particle sizes synthesized by citrate precursor route have been studied by x-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy. The observations suggest that the electronic processes depend sensitively on size, and a big variation occurs in the pattern of temperature dependence of isomer shift on changing the size from $5nm$ to $6nm$ and from $6nm$ to $7nm$⁠. The electron density at the nuclear sites first increases, then decreases and again increases as the temperature of the nanosize samples is increased from $12K$ to $400K$⁠. The electric-field gradient varies considerably as the size is changed, but remains almost independent of temperature for a particular size. It is concluded that different aspects of hyperfine interactions in nanophase become significant at different sizes.