Short-range B-site ordering in the inverse spinel ferrite NiFe_2O_4

摘要

The Raman spectra of single crystals of NiFe_2O_4 were studied in various scattering configurations in close comparison with the corresponding spectra of Ni-(0.7)Zn_(0.3)Fe_2O_4 and Fe_3O_4. 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 Fd3m space group. We argue that the experimental results can be explained by considering the short-range 1:1 ordering of Ni~(2+) and Fe~(3+) at the B sites of inverse spinel structure, most probably of tetragonal P4_122/P4_322 symmetry.