Experimental determination of the frequency and field dependence of Specific Loss Power in Magnetic Fluid Hyperthermia

Magnetic nanoparticles are promising systems for biomedical applications and in particular for Magnetic
Fluid Hyperthermia, a therapy that utilizes the heat released by such systems to damage tumor cells. We
present an experimental study of the physical properties that influences the capability of heat release, i.e.
the Specific Loss Power, SLP, of three biocompatible ferrofluid samples having a magnetic core of maghemite
with different diameter d = 10.2, 14.6 and 19.7 nm. The SLP was measured as a function of frequency
f and intensity H of the applied alternating magnetic field, and it turned out to depend on the core diameter,
as expected. The results allowed us to highlight experimentally that the physical mechanism
responsible for the heating is size-dependent and to establish, at applied constant frequency, the phenomenological
functional relationship SLP = cH^x, with 2sample size and field frequency, here chosen in the typical range of operating magnetic hyperthermia
devices. For the smallest sample, the effective relaxation time t_eff 19.5 ns obtained from SLP data is
in agreement with the value estimated from magnetization data, thus confirming the validity of the
Linear Response Theory model for this system at properly chosen field intensity and frequency.