Hysteresis power-loss heating of ferromagnetic nanoparticles designed for magnetic thermoablation

We have fabricated ferromagnetic Fe-oxide nanoparticles as a candidate of hysteresis-loss heating materials used for hyperthermia and thermoablation and examined heating abilities. The coercivities were controlled in a range between 50 Oe and 240 Oe. The temperature-rising characteristics were examined for randomly oriented solid nanoparticles by applying a 17-kHz ac magnetic field with an amplitude up to 550 Oe. A temperature rising rate [DELTA]/[DELTA]t was proportional to the square of the peak magnetic field Ho in the lower Ho region; however, the relation dose not hold at higher [H.sub.o]. The maximum loss power was obtained to be 4 W/g, which is smaller than the value expected from the minor loop experiment (13.7 W/g). The reason for small heating capability is discussed. Index Terms--Hyperthermia, hysteresis loss, iron oxide, magnetite, nanoparticle, thermoablation.