Magneto-thermal properties of Co-doped maghemite (γ-Fe2O3) nanoparticles for magnetic hyperthermia applications

Abstract

We report the preparation, characterization, and heating efficiencies of undoped and Cobalt (Co)-doped maghemite (γ-Fe2O3) nanoparticles (NPs) for magnetic hyperthermia applications. The structural, magnetic properties and heating ability of the as-synthesized NPs were fully characterized. XRD and Rietveld analysis showed the formation of single cubic phase of γ-Fe2O3, where doping with Co did not alter either the crystal structure or the lattice parameter. It was found that Fe ions are tetrahedrally and octahedrally coordinated to oxygens and that Co ions occupy the octahedral sites in Co-doped samples. Magnetic measurements displayed increase of magnetic saturation (Ms) with increasing Co concentrations from 0 to 5% (53.14–67.49 emu/g), with negligible coercive field and remanence suggesting superparamagnetic behavior. Langevin model and the law of approach to saturation (LAS) were used to confirm superparamagnetism and to determine the effective anisotropy constant (Keff), respectively. Temperature rise under an alternating magnetic field (AMF) were conducted, indicating that all the samples have high heating efficiencies and reach hyperthermia temperatures (42 °C) in relatively short times (3–10 min). Interestingly, γ-Fe2O3 NPs reached 42 °C in only ∼4 min, while 1–5% Co-doped γ-Fe2O3NPs required ∼ 7–10 min to reach the same temperature. Surprisingly, SAR (122 W/g) and ILP (1.5 nHm2/kg) values of γ-Fe2O3 NPs were found to be higher compared to Co-doped γ-Fe2O3 counterparts, indicating better heating efficiency of γ-Fe2O3 NPs. The mechanism of heating and plausible reasoning for this observation is discussed. Nevertheless, the ILP values for both γ-Fe2O3 and 1–5% Co-doped γ-Fe2O3 NPs (0.52–1.5 nHm2/kg) are in the range reported for commercial ferrofluids, proving their good heating efficiencies, and making them promising candidates for magnetic hyperthermia applications.