Zero-Dimensional Graphene and Its Behavior under Mechanochemical Activation with Zinc Ferrite Nanoparticles

Abstract

Equimolar mixtures of zero-dimensional graphene (SkySpring Nanomaterials, 1–5 nm particle size) and zinc ferrite nanoparticles (Alfa Aesar, 50 nm particle size) were exposed to mechanochemical activation by high-energy ball milling for time intervals of 0–12 hours. Their structural and magnetic properties were analyzed by Mössbauer spectroscopy and magnetic measurements. The spectra of zinc ferrite milled without graphene were fitted with one quadrupole-split doublet (quadrupole splitting 0.5 mm/s, isomer shift 0.23 mm/s) and indicated that zinc ferrite was superparamagnetic. The line width of the doublet increased from 0.41 to 0.64 mm/s, which correlates with a reduction in particle size as effect of the ball milling processing performed. When graphene was added to the milling powders, the Mössbauer spectra showed the appearance of another quadrupole doublet, with a quadrupole splitting of 0.84 mm/s and an isomer shift of -0.38 mm/s. Its abundance to the spectrum remained constant to 4.48% while the milling time was increased. This second doublet could be related to carbon atoms occupying neighborhoods in the proximity of iron atoms. Hysteresis loops were recorded in an applied magnetic field of 5 T at a temperature of 5 K. A change in the approach to saturation of the loop was observed, with saturation being achieved for the sample milled for 12 hours with graphene. Zero-field-cooling-field-cooling (ZFC-FC) was performed on all samples between 5–300 K with an applied magnetic field of 200 Oe. Graphene was found to stabilize the magnetic properties of the milled system of powders to a blocking temperature of about 90 K.