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

Abstract

Spinel ferrite CuFe 2O 4 and solid solution of Cu 1− x Zn x Fe 2− y Ga yO 4 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 CuFe 2O 4 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.