Size dependence of the properties of hematite nanoparticles

Samples of nanoparticles of hematite (α-Fe 2 O 3 ) with average size between 6 and 27 nm have been studied by use of Mössbauer spectroscopy. The superparamagnetic relaxation was analysed on the basis of the Néel-Brown expression for the relaxation time, τ = τ 0 exp[ KV / kT ]. It was found that the value of τ 0 increases with increasing particle volume, V , whereas the magnetic anisotropy energy constant, K , decreases. The electric quadrupole interaction, the isomer shift and the magnetic hyperfine field extrapolated to 0 K were found to be essentially independent of particle size.