Structural and magnetic properties of ZnXCo1-XFe2O4 nanoparticles: Nonsaturation of magnetization

ZnXCo1-XFe2O4 nanoparticles were synthesized by sol-gel method and were annealed at two different temperatures; 500 degrees C and 900 degrees C in air for 2 h. Structural studies were carried out by X-ray diffraction and Fourier transformed infrared spectroscopy. The crystallite size didn't show any variation with the increase in Zn2+ concentration and was increased after annealing. The magnetization value at 300 K for the as-prepared samples increased from 53 emu/g to 60 emu/g when Zn2+ concentration increased from x= 0 to 0.2 and then it decreased to 11 emu/g for x=1. Similar magnetic behavior was also observed for the annealed samples with a peak at x=0.2. A very high magnetization value of 116 emu/g at 60 K was observed for the 900 degrees C annealed sample with x=0.4. The coercivity decreased monotonically with the increase in the Zn2+ concentration for both the as-prepared and the annealed samples. The magnetization and coercivity values were observed to be enhanced with the decrease in measurement temperature. The nonsaturation behavior of the magnetic hysteresis loops of these nanoparticle samples observed for all compositions and temperatures was studied by the method of approach to saturation by fitting M(H)=M(infinity) [ 1-(H*/H) (1/2)] to the high field data of the initial curve from 20 kOe to 30 kOe. It was observed that H* value which is the measure of the nonsaturation increased with the increase in the Zn2+ concentration. The observed magnetic properties in these nanoparticle samples can be ascribed to the changed cation distribution in the spinel structure and to the decrease of Co2+ concentration.