Structural, magnetic and dielectric properties of Gd^sup 3+^ substituted NiFe^sub 2^O^sub 4^ nanoparticles

NiGdxFe2-xO4 nanoparticles with x = 0.0, 0.03, 0.05, 0.07, and 0.10 were synthesized by co-precipitation method and effect of Gd3+ substitution on various properties of nanocrystalline NiFe2O4 has been studied. Formation of single phase cubic mixed spinel structure is confirmed by X-ray diffraction and Raman spectroscopy and cations distribution has also been proposed from Rietveld refined data. Room temperature Mössbauer spectra showed two ferrimagnetic Zeeman sextets with one superparamagnetic doublet. Octahedral site occupancy of Gd3+ ions in these nanoparticles is suggested by Mössbauer parameters. Within the framework of X-ray photoelectron spectroscopy analysis, the ratio of cation concentration at tetrahedral and octahedral sites has been found to be consistent with proposed cation distribution. Magnetic measurements at room temperature exhibit the reduction in the saturation magnetization from 36 emu/gm to 4.9 emu/gm for x = 0.0 to 0.10 samples. The discrepancy in measured and calculated magnetic moment may be ascribed to the nonzero Yafet–Kittel angles of B site spins, which weaken A–B interaction. The coercivity decreases from 121 Oe to 48 Oe for x = 0.0 to 0.07 samples and again increases to 153 Oe for x = 0.10 sample. The degree of inversion calculated by Raman analysis varies with Gd3+ concentration which is supported by the variation of coercivity. The calculated spin numbers from electron spin resonance spectra decreases with Gd3+ doping which confirms the reduction in magnetization. Both dielectric constant and dielectric loss are found to decrease with the Gd3+ substitution because of the reduced hopping rate for Fe3+ at the octahedral sites in doped nanoparticles. Lower values of dielectric loss suggest that Gd3+ doped NiFe2O4 nanoparticles are suitable for high frequency microwave device applications.