Silica encapsulated manganese perovskite nanoparticles for magnetically induced hyperthermia without the risk of overheating O Kaman 1,2 , E Pollert 1 , P Veverka 1 , M Veverka 1 , E Hadová 1 , K Knížek 1 , M Maryško 1 , P Kašpar 3 , M Klementová 4 , V Grünwaldová 5 , S Vasseur 6 , R Epherre 6 , S Mornet 6 , G Goglio 6 , E Duguet 6 1 Institute of Physics, AS CR, v. v. i., Cukrovarnická 10/112, 162 53, Prague 6, Czech Republic 2 Charles University in Prague, Faculty of Science, Department of Inorganic Chemistry, Hlavova 8, 128 40, Prague 2, Czech Republic 3 Czech Technical University, Faculty of Electrical Engineering, Technická 2, 166 27, Prague 6, Czech Republic 4 Institute of Inorganic Chemistry, AS CR, v. v. i., 250 68, Řež u Prahy, Czech Republic 5 Zentiva a. s., U kabelovny 130, 102 37, Prague 10, Czech Republic 6 CNRS/Université Bordeaux, Institut de Chimie de la Matière Condensée de Bordeaux, 87 Avenue du Docteur Schweitzer, 33608, Pessac, France E-mail: kaman@fzu.cz Abstract. Nanoparticles of manganese perovskite of the composition La0.75Sr0.25MnO3 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 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. Keywords: Manganese perovskites; Magnetic nanoparticles; Magnetic hyperthermia; Silica coating, Core-shell particles PACS: 75.50.T, 81.07.Bc, 81.20.Fw 1.Introduction Magnetic nanoparticles attract attention due to a wide variety of promising applications including catalysis, data storage and biomedicine [1]. They can be exploited like agents for magnetically driven drug delivery, for the detoxification of biological fluids and tissue repair as well as contrast agents for magnetic resonance imaging (MRI) [2-4]. Furthermore hyperthermia induced by magnetic nanoparticles, first reported in 1957 by Gilchrist et al [5] who carried out hyperthermia on tissue samples using maghemite nanoparticles under an ac field of 1.2 MHz, was established to be a method of treating cancer based on local heating of the particles in a high-frequency magnetic field leading to the thermal destruction of the cancer cells [6-9]. With respect to the nature of heat production in the ac field, two classes of particles have to be distinguished. For the ferromagnetic or ferrimagnetic nanoparticles the heating originates from the hysteresis power losses. In contrast, the heating of superparamagnetic particles is given by rotation of their whole magnetic moments (Néel relaxation). Finally the rotation of the particles under the ac field (Brownian rotation) can contribute to the dissipation of energy by means of friction forces [10]. Requirements put on the used core materials appear to be not only high specific power losses in order to minimize the injected dose, but also a self-controlled heating mechanism ruling out the risk of local