Mechanical Milling and Comprehensive Characterization of Dysprosium Oxide-Hematite Magnetic Ceramic Nanostructures

Magnetic ceramic nanostructures of the type xDy2O3-(1-x)alpha-Fe2O3 (x=0.1 and 0.5) were synthesized by mechanochemical activation for ball milling times of 0, 2, 4, 8 and 12 hours. The 0-h Mӧssbauer spectrum was analyzed with a sextet characteristic to hematite. A second sextet for x=0.5 and a second and third sextet for x=0.1, with lower values of the hyperfine magnetic field, were assigned to dysprosium-doped hematite. An additional quadrupole-split doublet, whose relative abundance increased with the ball milling time and molar concentration, was assigned to superparamagnetic dysprosium iron perovskite (dysprosium orthoferrite) phase. The X-ray diffraction (XRD) patterns for the molar concentration x=0.5 showed the presence of DyFeO3 peaks after 12 h of milling. The hysteresis loops recorded at 5 K and an applied magnetic field of 5 T exhibited coercive fields that increased with ball milling time, while the hysteresis loops at 300 K were consistent with a strong paramagnetic component. The zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe and 5-300 K showed the effect of milling time on the Morin transition of hematite. The optical diffuse reflectance spectra showed that the samples were semiconductors with a band gap of ~2.1 eV.