Heating ability of magnetite nanobeads with various sizes for magnetic hyperthermia at 120 kHz, a noninvasive frequency

We synthesized four kinds of magnetite particles having average sizes of 7, 18, 40, and 80 nm and investigated their heating ability when they were dispersed in an agar gel and exposed to an ac magnetic field at 120 kHz, a noninvasive frequency for anticancer hyperthermia. The particles 18 nm in average diameter gave the highest heating ability, though they exhibited narrow hysteresis loops as compared to the particles having average diameters of 40 and 80 nm. This indicates that hysteresis loss does not contribute much to the heat rise by the 120 kHz ac field, and Neel relaxation is dominantly contributing to the heat rise by the 18 nm sized particles. A calculation based on Neel relaxation loss gave a plausible explanation. (C) 2006 American Institute of Physics.