纳米厚微米宽磁铁矿晶体Verwey转变的尺寸效应
Size effects in the Verwey transition of nanometer-thick micron-wide magnetite crystals
摘要：
我们已经监测Verwey过渡微米宽，纳米厚的磁铁矿岛上的外延Ru膜上的Al 2 O3（0001）使用拉曼光谱。这些岛是通过高温氧辅助分子束外延生长的。低于100 K和厚度大于20 nm的拉曼光谱对应于那些在大块晶体和高品质薄膜的子Verwey磁铁矿结构中观察到的。在室温下的立方相模式的宽度是相似的最好的散装晶体中报道，表明类似的电子-声子相互作用的水平。冷却后的拉曼光谱的演变表明，对于厚于20 nm的岛，结构变化首先出现在150 K开始的温度和Verwey转变本身发生在115 K左右。然而，薄于20 nm的岛显示出非常不同的拉曼光谱，这表明当发生跃迁时，岛的电荷顺序与其较厚的对应物明显不同
英文摘要：
We have monitored the Verwey transition in micrometer-wide, nanometer-thick magnetite islands on epitaxial Ru films on Al2O3(0001) using Raman spectroscopy. The islands have been grown by high-temperature oxygen-assisted molecular beam epitaxy. Below 100 K and for thicknesses above 20 nm the Raman spectra correspond to those observed in bulk crystals and high quality thin films for the sub-Verwey magnetite structure. At room temperature the width of the cubic phase modes is similar to the best reported in bulk crystals, indicating a similar level of electron-phonon interaction. The evolution of the Raman spectra upon cooling suggests that for islands thicker than 20 nm, structural changes appear first at temperatures starting at 150 K and the Verwey transition itself takes place at around 115 K. However, islands thinner than 20 nm show a very different Raman spectra indicating that while a transition takes place, the charge order of the ultrathin islands differs markedly from their thicker counterparts
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