Synthesis and magnetic properties of Co1−xZnxFe2O4+γ nanoparticles as materials for magnetic fluid hyperthermia

Nanoparticles of the single spinel phase Co1−xZnxFe2O4+γ of mean size 3–23 nm, as determined by X-ray diffraction analysis, were synthesized by the co-precipitation method followed by a temperature treatment. Magnetic studies carried out in the range of 4.5–550 K revealed gradual transition from ferrimagnetic to superparamagnetic to paramagnetic behaviour depending on the composition and particle size. The observed behaviour indicates a broad distribution of volume sizes of the nanoparticles. Particular importance can be ascribed to the composition of x=0.6 where the observed transition temperature to the paramagnetic state at 310–334 K suggests applicability of this material for magnetic fluid hyperthermia in a self-controlled regime.