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In the quest for suitable materials for hyperthermia we explored the preparation and properties of nanoparticles of Co ferrite. The material was produced by coprecipitation from water solution of Co and Fe chlorides and afterwards annealed at 400, 600 and 800 °C. The resulting particles were characterized by XRD, TEM, Mössbauer spectroscopy, and dc and ac magnetometry. The heating experiments in ac magnetic fields of various amplitudes were performed with diluted systems of particles suspended in agarose gel and the results were interpreted on the basis of the ac magnetic losses measured at various temperatures. The increase of magnetic losses and consequently of the heating efficiency with increasing temperature is explained by the strong dependence of the constant of magnetocrystalline anisotropy of Co ferrite on temperature.

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Nanoparticles of manganese perovskite of the composition La(0.75)Sr(0.25)MnO(3) uniformly coated with silica were prepared by encapsulation of the magnetic cores (mean crystallite size 24 nm) using tetraethoxysilane followed by fractionation. The resulting hybrid particles form a stable suspension in an aqueous environment at physiological pH and possess a narrow hydrodynamic size distribution. Both calorimetric heating experiments and direct measurements of hysteresis loops in the alternating field revealed high specific power losses, further enhanced by the encapsulation procedure in the case of the coated particles. The corresponding results are discussed on the basis of complex characterization of the particles and especially detailed magnetic measurements. Moreover, the Curie temperature (335 K) of the selected magnetic cores resolves the risk of local overheating during hyperthermia treatment.