Gd³⁺ doped CoCr₂O₄ nanoparticles: tuning the physical properties and optimizing the hyperthermia efficacy

Tuning the physical properties of nanomaterials is essential to enhance their capabilities for modern technological applications. Incorporating appropriate dopant ions is expected to modify the physical properties of nanomaterials significantly. In this study, the microstructural, magnetic, electronic and optical properties of cobalt chromite nanoparticles have been tuned by incorporating Gd ions to obtain the optimized conditions for self-heating efficiency. Four chromite samples with varying Gd³⁺ dopant concentrations [CoGd Cr_2- O₄: x = 0, 0.04, 0.08 and 0.12] were prepared using the standard chemical co-precipitation method and their physical properties were explored thoroughly. The Gd³⁺ dopants in the host CoCr₂O₄ structure were shown to be capable of regulating the physical properties of the doped nanomaterials. Formation of a pure cubic spinel crystallographic phase together with size, shape and developed microstrain in the synthesized doped chromites were analyzed precisely and it was found that the mean size decreased gradually as the Gd content increased. Higher Gd content chromite nanoparticles showed a distinct blue shift in their absorption spectra and an increase in specific surface area, as evidenced by the BET study confirming the reduction in mean diameter. Substituted Gd ions also tuned the dielectric characteristics of the host chromite nanomaterial. A careful investigation of electrical conductivity in varying electric fields indicated that electron hopping occurs mostly during charge conduction. All the chromite samples exhibited lossy dielectric behavior as the dopant fraction increased. Introducing Gd ions in nanocrystalline cobalt chromite diluted the magnetic properties, which was evident from the reduction of the coercive field, and also provided the superparamagnetic ground state above 95 K. The spin-spiral transition became visible near 26 K as the Gd content in pure CoCr₂O₄ nanoparticles increased. The induction heating properties of nanosized chromite samples were modified using Gd doping, and the impacts of both the anisotropic energy barrier and magnetic dipole-dipole interactions on hyperthermia efficacy were extensively investigated. All of the prepared chromite samples at low concentration (1 mg mL^-1) attained temperatures between 34.7 °C and 35.7 °C from ambient temperature in 900 seconds with an observed drop in the induction heating temperature with increasing Gd content in nanosized cobalt chromites. It was observed that the dispersion level of nanoparticles in solution also determined the heating efficiency. It was observed that Gd doped CoCr₂O₄ nanoparticles have the potential to be used in magnetic hyperthermia applications.