Impact of the correlation between doping content and ions distribution in Gd-doped CoFe2O4 nanoparticles on their magnetic properties and heating efficiency

In the present work, this Gd-doped CoFe2O4 nanoparticles (CoGdxFe2-xO4 NPs) were synthesized successfully by the co-precipitation method. The Gd substitution has a significant influence on the structural parameters including a change in crystallite size, lattice parameter, and X-ray density as compared to the pristine CoFe2O4 NPs. The High-resolution Transmission Electron Microscopy images claim a small particle size in the range of 8.6–13.9 nm for all samples. Besides, the change in the radius of ions at tetrahedral and octahedral sites is a proof for distribution of Co2+ and Fe3+ ions under the impact of Gd doping. The change in the number of Co2+, Fe3+, and Gd3+ ions might lead to not only an increase in a total magnetic moment at tetrahedral and octahedral sites but also a change in the inter-interactions of ions at the octahedral lattice. As a result, the doped samples have smaller values of saturation magnetization (34.7–49.8 emu/g), magnetic anisotropy (26.14–31.59 kJ/m3) than that of the pure CoFe2O4 NPs. In contrast, the CoGd0.2Fe1.8O4 NPs have the highest value of specific absorption rate (150.4 W/g) at 1 mg/mL under ac magnetic field (the amplitude of 200 Oe and the frequency of 450 kHz) despite the reduction of their magnetic quantities. These results indicate the key role of the Gd dopant in the enhancement of the heating efficiency of CoGdxFe2-xO4 NPs.