Ferrite nanoparticles of 40 nm size have been obtained under the thermal decomposition of {bis-(cyclopentadienyl)iron}-ferrocene in the presence of oxalic acid at 453 K. The solventless solid state thermal reaction has been monitored by thermogravimetry. Morphology and structure of the ferrites obtained are investigated by scanning electron microscopy and X-ray powder diffraction technique, respectively, while the magnetic property of these materials are studied by dc magnetization study as well as Fe-57 Mossbauer spectroscopy. The results, observed from X-ray powder diffraction, magnetization measurement and Mossbauer spectroscopy, establish unequivocally that the ferrite materials obtained are hematite. The solid state reaction process has been discussed too. To the best of our knowledge, the presently observed solid state reaction leading to the formation of hematite nanoparticles using ferrocene takes place at the lowest temperature reported so far.