Graphite-doped hematite and magnetite nanoparticles systems (∼50 nm)
were prepared by mechanochemical activation for milling times ranging from 2 to
12 hours. Their structural and magnetic properties were studied by
57Fe Mössbauer spectroscopy. The spectra corresponding to
the hematite milled samples were analyzed by considering two sextets,
corresponding to the incorporation of carbon atoms into the iron oxide
structure. For ball milling time of 12 hours a quadrupole split doublet has been
added, representing the contribution of ultrafine particles. The
Mössbauer spectra of graphite-doped magnetite were resolved considering
a sextet and a magnetic hyperfine field distribution, corresponding to the
tetrahedral and octahedral sublattices of magnetite, respectively. A quadrupole
split doublet was incorporated in the fitting of the 12-hour milled sample. The
recoilless fraction for all samples was determined using our previously
developed dual absorber method. It was found that the recoilless fraction of the
graphite-doped hematite nanoparticles decreases as function of ball milling
time. The f factor of graphite-containing magnetite
nanoparticles for the tetrahedral sites stays constant, while that of the
octahedral sublattice decreases as function of ball milling time. These findings
reinforce the idea that carbon atoms exhibit preference for the octahedral sites
of magnetite.