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

We report on the magnetic and hyperthermia properties of 5.5 nm in diameter iron nanoparticles synthesized by organometallic chemistry, which display the bulk magnetization. Quantitative analysis of alternative susceptibility measurements allows the determination of the effective anisotropy Keff=1.3×105 J m−3. Hyperthermia measurements are performed at a magnetic field up to 66 mT and at frequencies in the range of 5–300 kHz. Maximum measured specific absorption rate (SAR) is 280 W/g. SAR displays a square dependence with the magnetic field below 30 mT but deviates from this power law at higher value. SAR is linear with the applied frequency for μ0H=19 mT. These results are discussed in the light of linear response theory.