Jahn-Teller effect and superparamagnetism in zn substituted copper-gallate ferrite

Spinel ferrite CuFe2O4 and solid solution of Cu1-xZnxFe2-yGayO4 with 0.0 <= x <= 0.5 are synthesized through the usual ceramic method. X-ray diffraction measurements confirm the presence of single-phase tetragonal structure with c/a > 1 for CuFe2O4 and compositions with x <= 0.1. The formation of the tetragonal phase in these samples is attributed to the presence of the cooperative Jahn-Teller Cu ion at the octahedral B-site in the spinel lattice. At the compositional parameter x >= 0.2, tetragonal-to-cubic transformation occurred and the lattice parameter a for the cubic unit cell is found to decrease with increasing Zn content x. 57 Fe Mbssbauer measurements at 293K for these compounds reveal superparamagnetic phase for samples with 0.0 <= x <= 0.2. In contrast, Mbssbauer spectra at 12 K for these materials show well ordered spectra where, the cation distribution and the hyperfine parameters are determined. (c) 2006 Elsevier B.V. All rights reserved.