Urchin-like structures of NiCo2O4: Effect of annealing on magnetic properties

The paper discusses the temperature and magnetic field dependence of magnetization of NiCo2O4 nanoparticles, heat-treated at 3 different temperatures, 350°C, 550°C and 750°C, for 3 hrs. X-ray diffraction reveals the evolution of different phase as a function of annealing temperatures. The FESEM micrographs reveal urchin-like morphology of NiCo2O4 nanoparticles. The saturation magnetization, coercivity is found to drastically reduced upon annealing. Upon annealing superparamagnetic blocking temperature increases initially from 198 K to 221 K but reduces to 59 K after annealing at 750°C. Evolution of phase structure upon annealing is found to have direct correlation observed changes in microstructural and magnetic properties.