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

E. LIMA JR.; MARCELO VAZQUEZ MANSILLA; DE BIASI, EMILIO; M. L. MOJICA PISCIOTTI; R. D. ZYSLER

Workshop; X Latin American 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  and  blocked  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, there are two possible situations: first, for a lower anisotropy field in comparison to the amplitude of the applied field (H0), 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  H0 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  dmag vs. d hyd 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.