Mechanochemical activation of yttrium iron garnet with and without graphene nanoparticles

Nanoparticles systems of yttrium iron garnet with and without graphene were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 hours. The samples were characterized by Mossbauer spectroscopy. The 0-h specimens were analyzed by considering 2 sextets, corresponding to the tetrahedral and octahedral sites of the yttrium iron garnet. The spectra of the milled samples were fitted with a third sextet with the hyperfine magnetic field characteristic to hematite and a quadrupole-split doublet representing superparamagnetic particles of the yttrium perovskite (orthoferrite) phase. The mechanism of ball milling activation was found consistent with the decomposition of the garnet into yttrium perovskite and hematite. A plot of the quadrupole doublet's abundance as function of ball milling time indicated that graphene retarded the precipitation of the perovskite. The increased linewidth of the doublet showed that carbon from graphene entered with preference the lattice of the yttrium orthoferrite.