V. Kuncser1, N. Iacob1, A. Kuncser1, P. Palade1, C. Comanescu1, R. Turcu2, G. Schinteie1
1National Institute of Materials Physics, 077125, Bucharest-Magurele, Romania
2National Institute of Isotopic and Molecular Technologies, Cluj-Napoca, Romania
Issues related to the magnetic response of complex systems consisting of different types of Fe oxide nanoparticles (with different shapes and aspect rations, non-interacting or forming assembles, etc.) with respect to magnetic hyperthermia effects are emphasized together with proposed theoretical and experimental solving items. Specific characterization methodologies based on temperature and field dependent Mössbauer spectroscopy and SQUID magnetometry deserving an adequate magnetic characterization of the nanoparticulate systems in respect to phase composition, local and long-range magnetic structure, intra- and inter-particle magnetic interactions and mainly to the magnetic relaxation phenomena of interest for heat transfer mechanisms in magnetic hyperthermia are underlined. The different methodologies for the correct evaluation of the specific absorption rate (SAR) from real experimental data taking into account also environmental loss factors are critically discussed. Micromagnetic simulations and complementary analytical tools are used in order to search for optimal shapes and sizes of non-interacting Fe oxide magnetic nanoparticles leading to enhanced specific absorption rates. A specific attention is provided to the effects of inter-particle (dipolar type) interactions on the magnetic relaxation effects in magnetic fluids of different volume fractions. It has been proven by micromagnetic simulations that the direct effect of the inter-particle dipolar interaction is not only an increased particle anisotropy energy but also a decrease of the characteristic time constant τ0, with direct influence on the efficiency of the heat transfer during potential hyperthermia treatments. Experimental determination of specific absorption rates on ferrofluids with similar nanoparticles but of different volume fractions as well as in case of ferrofluids with different shapes and size of nanoparticles are presented and discussed.