Size Effects in the Verwey Transition of Nanometer-Thick Micrometer-Wide Magnetite Crystals Article Swipe
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· 2022
· Open Access
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· DOI: https://doi.org/10.1021/acs.jpcc.2c03391
· OA: W4292421602
We have monitored the Verwey transition in micrometer-wide, nanometer-thick\nmagnetite islands on epitaxial Ru films on Al2O3(0001) using Raman\nspectroscopy. The islands have been grown by high-temperature oxygen-assisted\nmolecular beam epitaxy. Below 100 K and for thicknesses above 20 nm the Raman\nspectra correspond to those observed in bulk crystals and high quality thin\nfilms for the sub-Verwey magnetite structure. At room temperature the width of\nthe cubic phase modes is similar to the best reported in bulk crystals,\nindicating a similar level of electron-phonon interaction. The evolution of the\nRaman spectra upon cooling suggests that for islands thicker than 20 nm,\nstructural changes appear first at temperatures starting at 150 K and the\nVerwey transition itself takes place at around 115 K. However, islands thinner\nthan 20 nm show a very different Raman spectra indicating that while a\ntransition takes place, the charge order of the ultrathin islands differs\nmarkedly from their thicker counterparts\n
