Impact of alkaline earth metal ion substitution on the structural and temperature-dependent magnetic properties of NiFe2O4 nanoparticles

Nanocrystalline nickel ferrite materials substituted with Ba2+ and Sr2+ ions were synthesized by sol-gel auto combustion method. The chemical formula of these nickel ferrite materials is Ni1-xAxFe2O4 (A = Ba and Sr; x = 0, 0.1, and 0.2). The X-ray diffraction result confirmed the Fd 3 m space group with inverse spinel phase of the nanoparticles and calculated crystallite sizes were in the range of 33 to 23 nm which were decreased with Ba and Sr substitution. The Raman spectra reveal peaks associated with both tetrahedral and octahedral groups. In Srsubstituted NiFe2O4 samples, the Raman modes shifted to lower wavenumbers, while with Ba-substitution, the modes of NiFe2O4 samples shifted to higher wavenumbers. The optical band gap values decrease with of Ba and Sr doped samples. Energy-dispersive X-ray analysis confirmed the stoichiometry and homogeneity of the samples. From Magnetic measurements, both remanence and coercivity values were increased with an increase in Ba and Sr composition. The magnetic anisotropy constant K of the samples was determined from the isotherm magnetic curves and using the law of approach to saturation. The large anisotropy constant deduced at 4 K is 10.5 x 105 erg/cc for Sr-doped NFO samples.