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

Nano crystalline Ni0.5Zn0.5CrxFe2-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 Ni0.5Zn0.5Fe2O4 nano particles were annealed at 1000 degrees C, the crystallite size increased while the lattice constant decreased slightly. For, the Cr3+ substituted samples annealed at 1000 degrees C, the variation in lattice constant, bondlengths, Me-Me 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 degrees C for Ni0.5Zn0.5Fe2O4. 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 Ni0.5Zn0.5Fe2O4 nano particles has been attributed to the core-shell structure of the fine particles. When annealed at 1000 degrees C the saturation magnetization of Ni0.5Zn0.5Fe2O4 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 Ni0.5Zn0.5CrxFe2-xO4 nano particles annealed at 1000 degrees 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.