Short-Range B-site Ordering in Inverse Spinel Ferrite NiFe2O4

TL;DR

This study investigates the short-range B-site ordering in NiFe2O4 using Raman spectroscopy, revealing a lower symmetry structure due to Ni2+ and Fe3+ ordering, which impacts the material's microscopic properties.

Contribution

The paper provides experimental evidence for short-range B-site ordering in NiFe2O4 and proposes a specific tetragonal symmetry model to explain the observed Raman spectra.

Findings

Raman spectra show more modes than expected for normal spinel.

Most Raman lines indicate a symmetry lower than Fd-3m.

Evidence supports 1:1 Ni2+ and Fe3+ ordering at B-sites.

Abstract

The Raman spectra of single crystals of NiFe2O4 were studied in various scattering configurations in close comparison with the corresponding spectra of Ni0.7Zn0.3Fe2O4 and Fe3O4. The number of experimentally observed Raman modes exceeds significantly that expected for a normal spinel structure and the polarization properties of most of the Raman lines provide evidence for a microscopic symmetry lower than that given by the Fd-3m space group. We argue that the experimental results can be explained by considering the short range 1:1 ordering of Ni2+ and Fe3+ at the B-sites of inverse spinel structure, most probably of tetragonal P4_122/P4_322 symmetry.