Effects of annealing temperature on microstructural, magnetic properties, and specific absorption rate of Zn-Ni ferrite nanoparticles

Zn-Ni ferrite nanoparticles were successfully synthesized by coprecipitation method. The samples were annealed at various temperatures, i.e., 200 degrees C, 400 degrees C, 600 degrees C, 800 degrees C, and 1000 degrees C. The nanoparticles have the mixed spinel phase structure as confirmed by the X-ray diffraction patterns. The crystallite size was 15.1 nm and increased to 25.1 nm after annealing at 1000 degrees C. Transmission electron microscope images showed that the annealed sample exhibited better dispersion and grain boundaries compared to the as-prepared sample. Fourier transform infra-red spectra showed the existence of vibrations at 378 cm(-1) and 555 cm(-1), confirming bonding for mixed spinel ferrites. The hysteresis measurement by using vibrating sample magnetometer confirmed that the sample possessed soft magnetic properties with a coercivity of 45 Oe and increased after annealing. The saturation magnetization of the as-prepared sample was 11 emu g(-1), and increased to 58 emu g(-1) after annealing at a temperature of 800 and 1000 degrees C. The specific absorption rate (SAR) with an alternating current magnetic field (50 Hz and 100 Oe) of Zn-Ni ferrite before and after annealing (at 800 degrees C) was 63.7 and 92.4 mW g(-1), respectively. The results showed that annealing temperature has a significant role in determining the microstructural, the magnetic properties and the SAR of the nanoparticles.