Fe3O4 Nano-clusters for Ultrafast Hyperthermia*

In this work, we studied the hyperthermia behavior of chemically synthesized Fe3O4 nano-clusters (NCs). The PVP concentration was found to significantly affect the shape, size and magnetic properties of the NCs. TEM images show that the NCs have a mean diameter of $\le $100nm and consist of isolated Fe3O4 nanoparticles with a mean diameter of 6-8nm. Magnetic measurements show that the room-temperature saturation magnetization (Ms) value increases from 20.2 to 61.7emu/g with increase in PVP concentration from 0.5g to 4g. To increase the water solubility and stability of the NCs, the as-made materials were first functionalized by PVP and then by citrate ions. HR-TEM images suggest a flower-like morphology with 30-40nm mean diameter. Magnetic measurements revealed that these NCs are superparamagnetic with Ms of 39emu/g and 58emu/g for the PVP and citrate coated materials, respectively. Hyperthermia measurements on NCs in water solution (10mg/ml), with a 10kA/m applied field at 150kHz frequency, showed a temperature increase from 293 to 338K after only 79s of field exposure with a high rate of 0.57C/s for the citrate functionalized particles and a rate of 0.31C/s for the PVP coated particles.