Published online by Cambridge University Press: 21 December 2015
Graphite-doped hematite and magnetite nanoparticles systems (∼50 nm)were prepared by mechanochemical activation for milling times ranging from 2 to12 hours. Their structural and magnetic properties were studied by57Fe Mössbauer spectroscopy. The spectra corresponding tothe hematite milled samples were analyzed by considering two sextets,corresponding to the incorporation of carbon atoms into the iron oxidestructure. For ball milling time of 12 hours a quadrupole split doublet has beenadded, representing the contribution of ultrafine particles. TheMössbauer spectra of graphite-doped magnetite were resolved consideringa sextet and a magnetic hyperfine field distribution, corresponding to thetetrahedral and octahedral sublattices of magnetite, respectively. A quadrupolesplit doublet was incorporated in the fitting of the 12-hour milled sample. Therecoilless fraction for all samples was determined using our previouslydeveloped dual absorber method. It was found that the recoilless fraction of thegraphite-doped hematite nanoparticles decreases as function of ball millingtime. The f factor of graphite-containing magnetitenanoparticles for the tetrahedral sites stays constant, while that of theoctahedral sublattice decreases as function of ball milling time. These findingsreinforce the idea that carbon atoms exhibit preference for the octahedral sitesof magnetite.