Induced nucleation of haematite nanoparticles with superparamagnetic properties

The mechanism of induced nucleation of nearly monodisperse haematite nanoparticles, obtained after two hours of ageing via a novel solution-based chemical route, was clarified on the basis of x-ray diffractometry, Fourier transform infrared spectroscopy, transmission electron microscopy and x-ray photoelectron spectroscopy analysis. Due to the induction of acetic anions, the amounts of OH− groups on the ferrihydrite surface increased and thereby accelerated the transformation of ferrihydrite to haematite. Moreover, the complexes of acetic anions and Fe3+ ions controlled the solution supersaturation during the formation of monodisperse haematite nanoparticles. Superconducting quantum interference device (SQUID) measurements revealed superparamagnetic behaviour of as-prepared haematite nanoparticles above their blocking temperature of 45 K when the field of 50 Oe was applied.