Heating of magnetic fluids by a low frequency alternating magnetic field

G. Kronkalns - M. M. Maiorov - E. Blums

Institute of Physics, University of Latvia, 32 Miera, Salaspils, LV-2169, Latvia

Abstract
Soft ferrite Fe₃O₄ and hard ferrite CoFe₂O₄ particles are synthesized and dispersed in various hydrocarbons for experimental investigation of heat generation under the action of a kHz range AC magnetic field. Magnetic properties of colloids are measured by a vibration sample magnetometer in fields up to 1 T. Complex magnetic susceptibilities are measured in a frequency range of 20 Hz to 2 MHz at two temperatures (20\degC and 50\degC). Large amplitude up to 120 mT (95.5 kA/m) AC magnetic field energy dissipation in the samples is investigated experimentally. A remarkable heat generation in a 18 kHz frequency AC magnetic field is observed in dispersions of hard cobalt ferrite nanoparticles both in the liquid and in the solid matrix. The coercivity dependence on the temperature of powders extracted from MF samples with two different nanoparticle sizes is measured. Tables 1, Figs 8, Refs 63.