Summary: | Magnetic inductive heating (MIH) has been a topic of great interest because of its potential applications, especially in biomedicine. In this paper, the parameters characteristic for magnetic inductive heating power including maximum specific loss power (SLP<sub>max</sub>), optimal nanoparticle diameter (D<sub>c</sub>) and its width (ΔD<sub>c</sub>) are considered as being dependent on magnetic nanoparticle anisotropy (K). The calculated results suggest 3 different Néel-domination (N), overlapped Néel/Brownian (NB), and Brownian-domination (B) regions. The transition from NB- to B-region changes abruptly around critical anisotropy K<sub>c</sub>. For magnetic nanoparticles with low K (K < K<sub>c</sub>), the feature of SLP peaks is determined by a high value of D<sub>c</sub> and small ΔD<sub>c</sub> while those of the high K (K > K<sub>c</sub>) are opposite. The decreases of the SLP<sub>max</sub> when increasing polydispersity and viscosity are characterized by different rates of d(SLP<sub>max</sub>)/dσ and d(SLP<sub>max</sub>)/dη depending on each domination region. The critical anisotropy K<sub>c</sub> varies with the frequency of an alternating magnetic field. A possibility to improve heating power via increasing anisotropy is analyzed and deduced for Fe<sub>3</sub>O<sub>4</sub> magnetic nanoparticles. For MIH application, the monodispersity requirement for magnetic nanoparticles in the B-region is less stringent, while materials in the N- and/or NB-regions are much more favorable in high viscous media. Experimental results on viscosity dependence of SLP for CoFe<sub>2</sub>O<sub>4</sub> and MnFe<sub>2</sub>O<sub>4</sub> ferrofluids are in good agreement with the calculations. These results indicated that magnetic nanoparticles in the N- and/or NB-regions are in general better for application in elevated viscosity media.
|