Effects of Mechanochemical Activation on the Structural, Magnetic and Optical Properties of Yttrium Iron Garnet-Graphene Nanoparticles

Yttrium iron garnet nanoparticles have potential applications in sensing and microwave devices. In this study, nanoparticles systems were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h. The samples were subsequently characterized by Mossbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The 0-h specimens were analyzed by considering 2 sextets in the Mossbauer spectra, corresponding to the tetrahedral and octahedral sites of the yttrium iron garnet structure. 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 iron perovskite (yttrium orthoferrite) phase. The mechanism of the ball milling activation was found to be consistent with the decomposition of the garnet into yttrium iron perovskite and iron oxide phases. A different set of yttrium iron garnet samples was milled with graphene nanoparticles (3 nm in diameter) and analyzed using the same techniques. Examination of the quadrupole doublet’s abundance as function of ball milling time indicated that graphene slowed down the precipitation of the perovskite. The increased linewidth of the doublet showed that the carbon from graphene preferentially entered the lattice of the yttrium orthoferrite. The coercive field of the sample milled with graphene is greater than that of the garnet and is even greater when longer milling times are employed and the particle size is smaller. The saturation magnetization decreases with decreasing particle size for prolonged milling due to the occurrence of the antiferromagnetic yttrium iron perovskite phase. The enhanced absorption in the infrared region could be associated with the incorporation of carbon from graphene in the lattice of the yttrium orthoferrite.