Characterization of ferromagnetic powders for magnetopneumography and other applications

Characterization of ferromagnetic materials in the form of powders and dusts is required in many practical applications. Among them are biomedical applications like magnetopneumography and magnetic hyperthermia. In both cases, specific problems make the accurate measurement difficult. In magnetopneumography, the amount and distribution of ferromagnetic dust inhaled in human lungs is estimated from remanent magnetic field. For quantitative conclusions, the magnetic properties of the inhaled dusts must be determined. In the case of hyperthermia therapy, the tissue is heated using high frequency magnetic field. The transfer of energy is facilitated with colloidal ferromagnetic nanoparticles. In order to prevent excessive overheating, as a safety measure, the Curie temperature of the particles is tuned just above the required treatment temperature (40-60 degrees C). However, this represents challenging conditions for the measurement of dynamic hysteresis loops of the powder specimen. The excitation causes rapid overheating above Curie temperature and disappearing of the signal. We describe the practical experience with static and dynamic characterization of powder specimens.