Browsing by Subject "magnetite"

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    Discovery of the soft electronic modes of the trimeron order in magnetite
    (2020-02-02) Baldini, Edoardo; Belvin, Carina A.; Rodriguez-Vega, Martin; Ozel, Ilkem Ozge; Legut, Dominik; Kozłowski, Andrzej; Oleś, Andrzej M.; Parlinski, Krzysztof; Piekarz, Przemysław; Lorenzana, José; Fiete, Gregory A.; Gedik, Nuh
    The Verwey transition in magnetite (Fe3O4) is the first metal-insulator transition ever observed [1] and involves a concomitant structural rear- rangement and charge-orbital ordering. Due to the complex interplay of these intertwined de- grees of freedom, a complete characterization of the low-temperature phase of magnetite and the mechanism driving the transition have long re- mained elusive. It was demonstrated in recent years that the fundamental building blocks of the charge-ordered structure are three-site small po- larons called trimerons [2]. However, electronic collective modes of this trimeron order have not been detected to date, and thus an understand- ing of the dynamics of the Verwey transition from an electronic point of view is still lack- ing. Here, we discover spectroscopic signatures of the low-energy electronic excitations of the trimeron network using terahertz light. By driv- ing these modes coherently with an ultrashort laser pulse, we reveal their critical softening and hence demonstrate their direct involvement in the Verwey transition. These findings represent the first observation of soft modes in magnetite and shed new light on the cooperative mechanism at the origin of its exotic ground state.
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    Synthesis and Photocatalytic Performance of TiO2-CNT and Magnetized Fe3O4-TiO2-CNT Multifunctional Hybrids: A Pickering Emulsion Platform for Organic Degradation
    (2018) Mason, Erica; Saleh, Navid
    The oil and textile industries produce billions of gallons of wastewater containing toxic, and sometimes carcinogenic or mutagenic, chemicals that often disperse throughout wastewater as suspended oil droplets. Photocatalytic degradation is a promising method for organic degradation, but needs to be improved. Tuning the photoactivity of a photocatalyst, enhancing the reactor design, and ensuring a facile method to remove the photocatalysts from the purified wastewater will help photocatalysis become a realistic option for use in advanced water treatment plants. Thus, this study set out to engineer an efficient and reusable method to degrade dispersed organic chemicals, by combining the photocatalytic properties of titania (TiO2), the electronic and hydrophobic properties of carbon nanotubes (CNTs), the magnetic abilities of iron oxide magnetite (Fe3O4), and the novel reactor design of Pickering emulsions. In this study, CNTs were hybridized with TiO2 and magnetized with Fe3O4 following a sol-gel method in order to form TiO2-CNTs and magnetic Fe3O4-TiO2-CNTs. The nanohybrids were used to stabilize Pickering emulsions, and preliminary dye degradation was demonstrated.