Structural, electrical and magnetic properties of Sr doped nickel ferrite using sol-gel auto combustion route

摘要

Nanocrystalline undoped and strontium doped nickel ferrite particles are synthesized using sol-gel auto combustion method with citric acid as the chelating agent. X-ray diffraction patterns reveal the formation of pure spinel ferrite structure with lattice parameters of 8.329 A and 8.332 A for undoped and Sr doped nanoparticles respectively. FTIR spectra show two main absorption bands such as the stretching and bending vibrations of the prepared spinel ferrite. The high-frequency absorption band υ_1 at 592-584 cm~(-1) is assigned to the stretching vibration of the tetrahedral metal-oxygen and lower frequency absorption band υ_2 at 403-406 cm~(-1) is attributed to the vibrations of octahedral (Fe-O) modes of Ni_(1-x)Sr_xFe_2O_4. The Raman spectra confirm the formation of cubic spinel structure. The prepared Ni_(1-x)Sr_xFe_2O_4 samples show five active modes such as A_(1g)+E_g+3T_(2g). AC electrical conductivity of prepared samples show frequency-dependent behaviour and it obeys the Jonscher's universal power law. The conductivity increases with increasing frequency. It indicates that the conductive grains become more active thereby promoting the hopping between Fe~(3+) and Fe~(2+) ions, which enhance the hopping conduction. The dielectric constant decreases sharply at low frequency region and attains constant value at high frequency. The magnetic measurements of Ni_(1-x)Sr_xFe_2O_4 nanoparticles are measured at 10 K and 300 K. It shows that increased coercivity and good saturation at 10 K due to strontium doping.