Magnetic anisotropy determination and magnetic hyperthermia properties of small Fe nanoparticles in the superparamagnetic regime

摘要

We report on the magnetic and hyperthermia properties of iron nanoparticlessynthesized by organometallic chemistry. They are 5.5 nm in diameter anddisplay a saturation magnetization close to the bulk one. Magnetic propertiesare dominated by the contribution of aggregates of nanoparticles with respectto individual isolated nanoparticles. Alternative susceptibility measurementsare been performed on a low interacting system obtained after eliminating theaggregates by centrifugation. A quantitative analysis using the Gittleman smodel allow a determination of the effective anisotropy Keff = 1.3 * 10^5J.m^{-3}, more than two times the magnetocristalline value of bulk iron.Hyperthermia measurements are performed on agglomerates of nanoparticles at amagnetic field up to 66 mT and at frequencies in the range 5-300 kHz. Maximummeasured SAR is 280 W/g at 300 kHz and 66 mT. Specific absorption rate (SAR)displays a square dependence with the magnetic field below 30 mT but deviatesfrom this power law at higher value. SAR is linear with the applied frequencyfor mu_0H=19 mT. The deviations from the linear response theory are discussed.A refined estimation of the optimal size of iron nanoparticles for hyperthermiaapplications is provided using the determined effective anisotropy value.