Tuning the microstructural, optical and superexchange interactions with rare earth Eu doping in nickel ferrite nanoparticles

A methodical study on structural, magnetic and optical properties of Eu doped NiFe2O4 nanoparticles with generic composition NiEuxFe2-xO4 = 0.00, 0.02, 0.04 and 0.06), synthesized via co-precipitation technique has been reported in this article. The fabrication of single phase ferrite nanoparticles was verified using X-ray powder diffractograms. The analysis of W-H plots revealed the presence tensile strain in the samples along with an average crystallite size of 20 +/- 4 nm. The existence lowering of cubic symmetry at octahedral sublattices was detected by vibrational Raman spectra recorded at 300 K. The values of indirect optical band gap were noted in the range of 1.76 +/- 0.02 eV. The hysteresis loops at room temperature supported the paramagnetic character of Eu3+ ions in spinel structure. The evidence of reduced A-O-B superexchange interaction along with reduction of saturation magnetization was also found for higher Eu content nanoparticles at 300 K. The coercivity was observed to increase at 5 K. The blocking temperature and thereto-magnetic irreversibility was reduced with increasing Eu concentration.