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Item type:Publication, Structural, hyperfine, and magnetic evolution of a natural magnetite–serpentine composite: Effects of magnetic separation and thermal treatment(Elsevier BV, 2026-08-15)In this work, the structural, hyperfine, and magnetic evolution of a natural magnetite–serpentine composite was systematically investigated in its as-collected state, after magnetic separation, and following thermal treatments. X-ray diffraction combined with Rietveld refinement reveals a lizardite-dominated matrix containing magnetite as the primary magnetic phase. Mössbauer spectroscopy identifies Fe2＋ and Fe3＋ cations distributed over distinct octahedral and tetrahedral sites in both lizardite and magnetite, providing insight into cation distribution and oxidation state evolution. Magnetic measurements reveal ferrimagnetic behavior dominated by magnetite, with a saturation magnetization of ∼79 emu g−1 at room temperature. The transition temperature was estimated from the derivative of the ZFC–FC magnetization curve with respect to temperature, which exhibits a relatively broad peak associated with the Verwey transition (118 K). This feature suggests the presence of relatively preserved magnetite within the ultramafic matrix, although the broad character of the transition may reflect structural disorder, particle-size effects, or magnetic interactions. In addition, the magnetic data indicate the coexistence of superparamagnetic behavior and possible spin-glass-like contributions, likely associated with surface disorder and nanoscale magnetic interactions. Water-assisted magnetic separation enhances the magnetic fraction, confirming that magnetite particles are embedded within the lizardite matrix. Thermal treatments at 500 °C and 1000 °C induce progressive dehydroxylation, oxidation of iron-bearing phases, and the formation of hematite, forsterite, silica, and clinoenstatite, leading to significant modifications in both hyperfine parameters and magnetic behavior. The results establish clear structure-hyperfine-magnetic correlations and demonstrate how magnetic separation and thermal processing govern the phase stability and functional magnetic response of natural magnetite–serpentine systems. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Spatially controlled sputtering of Mo1?xHfx thin films: Composition-tuned structure, electronic transport, and room-temperature CO2 sensing(Elsevier BV, 2026-09-30)Mo1−xHfx thin films with a compositional gradient were deposited by a co-sputtering process. Structural characterization by XRD, supported by Rietveld refinement, suggests that at low Hf concentrations the films exhibit an fcc-like structure, with a systematic increase in the lattice parameter as Hf content increases, consistent with Vegard's law. At higher Hf concentrations, the diffraction patterns evolve and are better described by a mixed-phase system involving hcp-Hf and bcc-Mo contributions, indicating the onset of phase coexistence. EDS confirms the compositional gradient and the effective incorporation of Hf into the Mo matrix, while scanning electron microscopy reveals position-dependent variations in morphology and thickness arising from different sputtering rates. XPS identifies the formation of native surface oxide layers and provides their chemical composition. Impedance spectroscopy measurements exhibit pronounced spatial variations in the electrical response, which are well described using equivalent electrical circuits and are consistent with the presence of these oxide layers. At Mo-rich regions, an inductive response is attributed to enhanced charge transport and current inertia effects in highly conductive areas. Finally, room-temperature gas-sensing measurements demonstrate an electrical response to CO2, revealing two distinct regimes: Hf-rich films exhibit an n-type-like response, whereas Mo-rich films show a p-type-like behavior.