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

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

Buenos Aires

Workshop; X Latin American Workshop on Magnetism, Magnetic Materials and their Applications (X LAW3M); 2013

LAW3M

Magnetic Fluid Hyperthermia (MFH) 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 (Néel) and blocked (hysteresis) regimes. For systems where Brown and Superparamagnetic 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, the heating generation should be calculated from the area of hysteresis loop, which is numerically calculated from the magnetic surface energy of system.For a real system, the limits among the regimes are strongly determined by the magnetic volume, the hydrodynamic volume, the viscosity of the medium, the frequency of the applied field and the magnetic anisotropy of the material. In this work, we explore the limits among these mechanisms as function of the later parameters. The frontier between the Néel and Brown mechanisms was determined by the relation $\tau_[N\´{e}el] = \tau_{Brown}$, and the heating generation was analytically calculated by the Rosensweig´s model. The region where the hysteresis dominates was determined by comparing the frequency of the applied field with the Néel and Brown relaxation times, and the heating generation was numerically calculated. This information was summarized in diagrams of $d_{magnetic} vs. d_{hydro}$ for different frequencies and anisotropies. We specifically calculated these diagrams and 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.