Effect of lattice strain on structure, morphology and magneto-dielectric properties of spinel NiGdxFe2−xO4 ferrite nano-crystallites synthesized by sol-gel route

Nanocrystalline powders of Gadolinium (Gd3+) substituted nickel ferrite spinel (NiGdxFe2−xO4: x = 0.00, 0.025, 0.050, 0.075 and 0.1) samples were synthesized via sol-gel method. Nickel nitrate hexahydrate and Ferric nitrate hexahydrate were used as the precursors and rare earth Gadolinium nitrate hexahydrate [Gd(NO3)3·6H2O] was used as the dopant. The structural, morphological, magnetic and dielectric properties of the synthesized nanoparticles were examined by XRD, FTIR, HRSEM, EDX, TEM, VSM and dielectric studies. The Scherrer method and Williamson-Hall (W-H) method were used to evaluate the crystallite sizes and lattice strain. The crystallite size of NiGdxFe2−xO4 samples were found to decrease from 25 nm to 11 nm with increase in Gd3+ content. Lattice parameters decrease and lattice strain increases with the increase in Gd3+ content in the sample. HRSEM images showed the spherical morphology and uniform size distribution. The elemental composition analysis confirms the stoichiometric presence of expected elements in the samples. The crystallite size and the particle size calculated from the XRD analysis and HRTEM monographs indicate the correlation of the data obtained from both the measurements. Magnetic studies of the samples were performed using vibrating Sample Magnetometer, in which magnetizations (Ms) decrease with increase in Gd3+ concentration from 36.51 emu/gm to 19.69 emu/gm. As the gadolinium content was gradually increased, coercivity and remnant magnetization were also decreased. Magnetic anisotropy of nickel ferrite was also found to decrease with increasing gadolinium content. The saturation magnetization values were achieved by using the “Law of Approach (LA) to Saturation magnetization” technique. Specific correlation between magnetic interaction and lattice strain was observed in Gd3+ substituted nickel ferrite. Dielectric parameters such as dielectric constant and dielectric loss of the prepared samples decrease with increase of applied frequency and increasing of Gd3+ doping concentration.