The fields of application of magnetic nanoparticles in medicine and biology appear to be continuously increasing, eg, cell sorting, bimolecular purification, drug delivery and contrast agents for MRI or mediators for local destruction of cancer cells by magnetic hyperthermia [1, 2]. Magnetic fluid hyperthermia attracts attention because it allows minimizing the side effects due to the localization of heat to the desired parts of organism. Two kinds of heating treatments are today distinguished: mild hyperthermia (immunotherapy) performed between 41–46◦ C and thermoablation (direct cell destruction) done at temperature between 46 and 56◦ C. It was well known from clinical experiments reported in 1970’s that tumor cells are more sensitive to temperatures in the range of 42–45◦ C than normal tissue cells. The exact temperature control at the tissue site is, therefore, very important because local overheating may damage safe tissue. From this point of view, magnetic particles may serve as a smart mediator thanks to the automatic switching off from heating at their Curie temperature. Several research reports have recently focused on synthesizing magnetic nanoparticles with Curie temperatures of some tens of degrees above body temperature [2–4]. An approach usually applied is a suitable solution in complex magnetic systems, eg, the investigation performed on nanoparticles of yttrium iron garnet diluted by aluminum, Y3Fe1− xAlxO12 [4]. In very recent papers by Kuzniesov et al.[6] and Vasseur et al.[7], the authors reported that manganite nanoparticles might be a “smart” material to serve