Radio frequency magnetic field induced heating of superparamagnetic nanoparticle dispersions: Probing the interplay between anisotropy and dipolar energy

Abstract

The effect of sample concentration on radio frequency magnetic field induced heating of oil-based dispersions of oleic acid capped superparamagnetic Fe3O4 nanoparticles was studied. The sample concentration was varied from 2.5-23 wt. % and field induced heating studies were carried out at a fixed frequency of 126 kHz and at five different amplitudes. Heating efficiency was foundto linearly increase with the square of field amplitudes, in accordance with the linear response theory. Theoretical results on heating efficiency, obtained from high frequency dynamic loop simulations, were in agreement with the experimental findings. The increase in heating efficiency with MNP concentration was attributed to the higher ratio of anisotropy energy to dipolar energy. With increase in MNP concentration, dipolar interaction did not enhance significantly, whereas effective number of heat sources per unit volume increased leading to a larger heating efficiency at higher loading.