Microwave-assisted benzyl alcohol route, starting form Fe(III) acetylacetonate, was applied to obtain crystalline magnetite nanoparticles. In particular the effect of synthesis time on the physical and magnetic properties of the so obtained powders were evaluated. By means of this approach, monocrystalline magnetite particles with size ranging from 4 to 8 nm were obtained. The crystallinity increases as the microwave thermal treatment is increased and reaches almost 95 wt% with treatment time of 240 min. The size of the units individually responding to a magnetic field is slightly larger than the nanoparticle size, indicating partial aggregation of nanoparticles. Both the magnetization of powders and the effects of magnetic dipolar interaction increase with increasing heating time. All powders behave as weakly interacting superparamagnetic materials over an extended temperature interval. (C) 2014 Elsevier B.V. All rights reserved.