Structural and Magnetic Studies on Chromium substituted Ni-Zn Nano Ferrite Synthesized by Citrate Gel Auto Combustion Method

Nano crystalline Ni_0.5Zn_0.5Cr_xFe_2?xO₄ particles with x varying from 0.00 to 0.25 in steps of 0.05 have been synthesized through citrate gel autocombustion method. When Ni_0.5Zn_0.5Fe₂O₄ nano particles were annealed at 1000 °C, the crystallite size increased while the lattice constant decreased slightly. For, the Cr³⁺ substituted samples annealed at 1000 °C, the variation in lattice constant, bondlengths, M_e-M_e distances and other structural parameters have been attributed to the dissimilarity in the ionic radius of the displaced (Fe³⁺) ion and the substituted (Cr³⁺) ion. Thermal studies indicated the autocombustion process which is an exothermic reaction between the nitrates salt solutions and the citric acid took place at about a temperature of 400 °C for Ni_0.5Zn_0.5Fe₂O₄. The M-H loops for all samples indicated a soft ferrite nature for all samples. The non-saturated hysteresis loop and high coercivity for the as prepared Ni_0.5Zn_0.5Fe₂O₄ nano particles has been attributed to the core-shell structure of the fine particles. When annealed at 1000 °C the saturation magnetization of Ni_0.5Zn_0.5Fe₂O₄ nano particles increased and attained the bulk value (70emu/gm). The specific saturation magnetization has been observed to decrease with increasing Cr³⁺ substitution and is ascribed to the reduction in the predominant A-B exchange interaction mechanism. By considering the site preferences cations a suitable distribution of the cations among the A & B-sites has been proposed for Ni_0.5Zn_0.5Cr_xFe_2?xO₄ nano particles annealed at 1000 °C and has been verified using the X-ray diffraction line intensity calculations. The FT-IR spectra of the annealed ferrite powders showed two significant absorption bands in the wave numbers around 400 cm^?1 & 580 cm^?1 and an additional shoulder at 360cm^?1. The position and width of the bands have been observed to vary with Cr³⁺ substitution. The results of IR spectra are in support of the proposed cation distribution.