Raman, infrared and Mossbauer spectroscopic studies of solid-state synthesized Ni-Zn ferrites

A set of Nickel-Zinc ferrite samples (Ni1-xZnxFe2O4, x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were synthesized by the low-energy ball milling method with subsequent thermal treatment. Infrared, Raman and Mossbauer spectroscopies were used to analyze the lattice dynamics and structure of the prepared samples. Infrared studies showed a dominant absorption band ranging from 548 cm(-1) to 592 cm(-1) associated with cation-oxygen stretching vibrations at tetrahedral sites. The five Raman modes, predicted by factor group analysis, were observed in all spectra. All these spectra changed in symmetry because of the incorporation of Zn into the lattice, and the reordering of Fe, Ni and Zn ions in both, tetrahedral (A) and octahedral [B] sites. It is observed that Fe3+ ions located at tetrahedral sites are gradually displaced to octahedral sites by the increase of Zn2+ ions. Mossbauer spectra were collected for all samples at 295 K and at 18 K. The spectra were properly fitted by using a model that assumes that the average hyperfine magnetic field at the octahedral sites is due to a random substitution of magnetically interacting Fe-A(3+) ions by diamagnetic Zn-A(2+) ions at the tetrahedral sites. It was found that the average supertransfered hyperfine field due to one Fe-A(3+) - O2+ - Fe-B(3+) superexchange interaction was equal to about 0.9 T at 18 K. The zinc contents at tetrahedral sites as obtained by Raman, Mossbauer and XRD techniques are compared and discussed.