Heat generation in agglomerated ferrite nanoparticles in an alternating magnetic field

Abstract

The role of agglomeration and magnetic nanoparticle interactions on the heating generation of magnetic ferrofluids in an ac magnetic field is unclear until now, with apparently discrepancy in the results presented in the literature. In this work, we have measured the heating generation capability of agglomerated ferrite nanoparticles in the non-invasive ac magnetic field with f = 100 kHz and H0 = 13 kA/m. The nanoparticles were morphological and magnetically characterized, and the Specific absorption rate (SAR) for our ac magnetic field presents a clear dependence with the diameter of the nanoparticles, with a maximum of SAR = 48 W/g at 15 nm. Our agglomerated nanoparticles have large hydrodynamic diameters, thus the mechanical relaxation can be not taken into account for the heating generation. Therefore, we present a model that simulates the SAR dependence of agglomerated samples with the diameter of the nanoparticles based on the hysteresis losses that is valid for the non-linear region (with H0 comparable to anisotropy field). Our model takes into account the magnetic interactions among the nanoparticles in the agglomerate. For comparison, we also measured the SAR of non-agglomerated nanoparticles in a similar diameter range, in which Néel and Brown relaxations dominate the heating generation.