Preparation of Magnetic Nanoparticles via a Chemically Induced Transition: Role of Treating Solution’s Temperature

Using FeOOH/Mg(OH)(2) as precursor and FeCl(2) as the treating solution, we prepared γ-Fe(2)O(3) based nanoparticles. The FeCl(2) treating solution catalyzes the chemical reactions, dismutation and oxygenation, leading to the formation of products FeCl(3) and Fe(2)O(3), respectively. The treating solution (FeCl(2)) accelerates dehydration of the FeOOH compound in the precursor and transforms it into the initial seed crystallite γ-Fe(2)O(3). Fe(2)O(3) grows epitaxially on the initial seed crystallite γ-Fe(2)O(3). The epitaxial layer has a magnetically silent surface, which does not have any magnetization contribution toward the breaking of crystal symmetry. FeCl(3) would be absorbed to form the FeCl(3)·6H(2)O surface layer outside the particles to form γ-Fe(2)O(3)/FeCl(3)·6H(2)O nanoparticles. When the treating solution’s temperature is below 70 °C, the dehydration reaction of FeOOH is incomplete and the as-prepared samples are a mixture of both FeOOH and γ-Fe(2)O(3)/FeCl(3)·6H(2)O nanoparticles. As the treating solution’s temperature increases from 70 to 90 °C, the contents of both FeCl(3)·6H(2)O and the epitaxial Fe(2)O(3) increased in totality.