Diagrams of Mechanisms for Heating Generation in a ferrofluid in the presence of ac magnetic field

E. LIMA JR.; E. DE BIASI; M. VASQUEZ MANSILLA; M. L. MOJICA PISICOTTI; R. D. ZYSLER

Workshop; Latin America Workshop on Magnetism, Magnetic Materials and their Applications; 2013

Magnetic Fluid Hyperthermia is a promising oncology protocol where the increment of temperature in a target tissue is achieved by the magnetic losses of a ferrofluid constituted by magnetic nanoparticles in a liquid medium in the presence of an ac magnetic field. Heating generation mechanism is described by two distinct relaxation processes of magnetization. One of these mechanisms is related to the mechanical movement of the particles in the fluid, the so called Brown relaxation process. The other relaxation process is related to the fluctuation of magnetization through energy barriers and it can be related with two regimes: superparamagnetic (N\´{e}el) and blocked (hysteresis) regimes. For systems where Brown and N\´{e}el regime are dominant, the heating generation can be described by the Rosensweig´s model, and it is calculated from the out-of-phase component of the ac susceptibility. For the blocked regime, there are two possible situations: first, for a lower anisotropy field in comparison to the amplitude of the applied field ($H_{0}$), it can be calculated by the area of hysteresis loop; second, for much higher anisotropy field, by the out-of-phase susceptibility component. For a real system, the limits among the regimes are strongly determined by the magnetic, morphological and rheological properties of the system, as well as from ($H_{0}$) and frequency of the applied field. In this work, we explore the limits among these mechanisms as function of the later parameters. This information was summarized in diagrams of $d_{magnetic} vs. d_{hydro}$ for different frequencies and anisotropies. We specifically calculated these diagrams and also calculated the heating generation for the distinct mechanisms. From these results, the dominant mechanism of the heating generation can be determined and the parameters of the system can be tuned in order to optimize the heating generation of a ferrofluid in an ac magnetic field.