Effect of Frequency and Field Amplitude in Magnetic Hyperthermia

We have undertaken studies of the heating rate in three sets of magnetic nanoparticles for their application in magnetic hyperthermia. The nanoparticles were magnetite-maghemite with average particle diameters of 5, 28, and 45 nm, respectively. All samples were synthesized in an aqueous media and have a narrow size distribution. These sizes represent particles which are single domain, particles which lie close to the single domain multi-domain boundary, and particles which are probably multidomain. The heating rate is greater for the largest particles when an alternating magnetic field of 250 Oe and a frequency of 110 kHz are applied. The significant increase in heating for the 45 nm particles suggests that heating may be associated with particle rotation.