Nanostructured iridium oxide-hematite magnetic ceramic semiconductors

xIrO2–(1−x)α-Fe2O3 (x=0.1, 0.3 and 0.5) nanoparticle systems were successfully synthesized by mechanochemical activation of IrO2 and α-Fe2O3 mixtures for 0–12 h of ball milling time. The study aims at exploring the formation of magnetic oxide semiconductors at the nanoscale, which is of crucial importance for catalysis, sensing and electrochemical applications. X-ray powder diffraction (XRD), Mössbauer spectroscopy, magnetic measurements and simultaneous differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were used to study the phase evolution of xIrO2–(1−x)α-Fe2O3 nanoparticle systems under the mechanochemical activation process. Rietveld refinement of the XRD patterns yielded the values of the particle size and lattice parameters as function of composition and milling times and indicated the presence of Ir-substituted hematite and Fe-doped iridium oxide for large x values and long milling times. The Mössbauer studies showed that the spectrum of the mechanochemically activated composites evolved from a sextet for hematite to sextets and a doublet upon duration of the milling process with iridium oxide. Magnetic measurements recorded at 5 K in an applied magnetic field of 40,000 Oe showed that the saturation magnetization of the milled samples increased with ball milling time while preserving a multidomain magnetic structure. The unmilled sample at 5 K showed a spin-flop type metamagnetic transition around 30,000 Oe. The Morin transformation was evidenced by zero-field cooling–field cooling (ZFC–FC) measurements in 200 Oe and 1 T and the transformation characteristic temperatures were shifted to lower values.