Structural, magnetic and electrical properties of nanocrystalline zinc ferrite

Nanoparticles of ZnFe₂O₄ with grain size of 30 nm have been synthesized via sol-gel auto combustion method and characterized using DSC (differential scanning calorimetry), XRD (X-ray diffraction), SEM (scanning electron microscopy), EDAX (energy dispersive X-ray analysis), FTIR (Fourier transform infrared spectroscopy), VSM (vibrating sample magnetometer) and Ac-electrical conductivity measurement setup. Structural analysis using XRD and FTIR show the formation of spinel structure in nano ZnFe₂O₄ particles. The cation distribution in the sample has been estimated theoretically and the results show that as-prepared nanoparticles of ZnFe₂O₄ have partially inverted ionic distribution in comparison with that of bulk zinc ferrite. Results from EDAX indicate the ratio of Fe:Zn as close to 2:1. The presence of a weak ferrimagnetic phase for nano ZnFe₂O₄ at room temperature has been established from its hysteresis behavior. Redistribution of cations occurring at nano-regime and surface spin canting of nanoparticles of ZnFe₂O₄ are expected to be responsible for the presence of magnetic ordering in nano ZnFe₂O₄. The Curie temperature of nano ZnFe₂O₄ determined from magnetization versus temperature measurement is equal to 375 °C. The electrical conductivity of the present ZnFe₂O₄ at a frequency of 100 kHz at room temperature is observed to be 2.11 × 10⁻⁸ Ω⁻¹ cm⁻¹ which is four orders lesser in magnitude than the value of bulk ZnFe₂O₄. Overall conductivity response with respect to temperature and frequency confirm that ZnFe₂O₄ tends to become more dielectric in the nano-regime.