Observation of superparamagnetism in ultra-fine ZnxFe1−xFe2O4 nanocrystals synthesized by co-precipitation method

Abstract

Ultra-fine nanocrystals of ZnxFe1−xFe2O4 (x=0.1, 0.3, 0.5 and 0.7) have been synthesized by chemical co-precipitation method at low temperature (∼60°C). Rietveld fitted X-ray diffraction patterns confirm the formation of cubic spinel structure with Fd-3m space group. High resolution transmission electron microscopy (HRTEM) analysis reveals that the average particle size reduces with the substitution of higher Zn concentration from 12 to 3nm for sample x=0.1 to 0.7. Vibrating sample magnetometer (VSM) results indicate that the blocking temperature (TB) for sample x=0.1 is 120K and significantly decreases up to less than 5K as we move towards the sample x=0.7. Moreover, the observed irreversible magnetization (∆M=MFC−MZFC), coercivity and remanence are indistinguishable for sample x=0.7 down to 5K, which infers the superparamagnetic behaviour in this sample in a wide range of temperature from room temperature down to 5K. The reduction in peak to peak line width and enhanced magnetic field asymmetry observed in electron paramagnetic resonance (EPR) spectra also supports the presence of superparamagnetism in sample x=0.7.