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>1for 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. 57Fe Mössbauer measurements at 293 K for these compounds reveal superparamagnetic phase for samples with 0.0⩽x⩽0.2. In contrast, Mössbauer spectra at 12 K for these materials show well ordered spectra where, the cation distribution and the hyperfine parameters are determined.