Audio-frequency heating of particulate magnetic systems

This paper presents theoretical and experimental studies on the magnetodynamics and energy dissipation in suspensions of small ferromagnetic particles with magnetic hysteresis and mechanical mobility in an AC magnetic field. Energy absorption by particles suspended in a solid, liquid or gas environment and subjected to high frequency magnetic fields is of great interest for cancer treatment by hyperthermia, chemical technology, biotechnology and smart materials science.

Sub-micron needle-like γ-Fe₂O₃ particles dispersed in liquid were subjected in this study to a 430 Hz magnetic field with an intensity of up to 10⁵ A/m. Dynamic magnetization loops were measured in parallel to the energy dissipated in the samples. Combined magnetomechanical dynamics of particle dispersions was simulated by using a chain-of-spheres model allowing for incoherent magnetic field reversal. In liquid dispersions, within the kilohertz frequency range, the mechanical mobility of particles does not interfere with their hysteretic magnetic reversal that makes heat release comparable to that observed with solids; for instance, in the present study using γ-Fe₂O₃ particles in liquid subjected to 10⁴ Hz field exhibited heat release rates from 250 up to 600 W per 1 cm³ of the dry particle content.