Orthorhombic Ti2O3: A Polymorph-Dependent Narrow-Bandgap Ferromagnetic Oxide
Orthorhombic Ti2O3: A Polymorph-Dependent Narrow-Bandgap Ferromagnetic Oxide
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斜方 Ti2O3：一种多晶型相关的窄带隙铁磁氧化物
DOI：
10.1002/adfm.201705657
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发表时间：
2018-02-14
影响因子：
19
通讯作者：
Wu, Tom
中科院分区：
文献类型：
--
作者：
Li, Yangyang;Weng, Yakui;Wu, Tom
磁性半导体在自旋电子学中备受追捧，它不仅可以像传统电子学那样控制载流子，还可以控制自旋态。然而，几乎所有已知的磁性半导体的带隙都大于1 eV，这限制了它们在长波长区域的应用。在这项工作中，发现了一种独特的窄禁带(约0.1 eV)铁磁氧化物半导体--正交结构的Ti2O_3薄膜。相反，众所周知的刚玉结构的Ti2O3多晶型具有反铁磁性基态。这项对外延Ti2O_3薄膜的综合研究揭示了结构、电学和磁性之间的强相关性。发现新的正交型Ti2O_3多晶型具有很高的电子浓度，而体型三角结构的TiO_2O_3是p型。更有趣的是，与三角块体Ti2O_3的反铁磁性基态相反，在正交结构的Ti2O_3中观察到了意外的铁磁性，其转变温度远高于室温，这一点得到了X射线磁性圆二色谱的证实。用第一性原理计算，铁磁性归因于正交型Ti2O_3中的一种特殊类型的氧空位。在正交结构的Ti2O_3中观察到的室温铁磁性，展示了一种通过选择稳定晶型相来控制外延氧化膜磁性的新途径。
Magnetic semiconductors are highly sought in spintronics, which allow not only the control of charge carriers like in traditional electronics, but also the control of spin states. However, almost all known magnetic semiconductors are featured with bandgaps larger than 1 eV, which limits their applications in long-wavelength regimes. In this work, the discovery of orthorhombic-structured Ti2O3 films is reported as a unique narrow-bandgap (approximate to 0.1 eV) ferromagnetic oxide semiconductor. In contrast, the well-known corundum-structured Ti2O3 polymorph has an antiferromagnetic ground state. This comprehensive study on epitaxial Ti2O3 thin films reveals strong correlations between structure, electrical, and magnetic properties. The new orthorhombic Ti2O3 polymorph is found to be n-type with a very high electron concentration, while the bulk-type trigonal-structured Ti2O3 is p-type. More interestingly, in contrast to the antiferromagnetic ground state of trigonal bulk Ti2O3, unexpected ferromagnetism with a transition temperature well above room temperature is observed in the orthorhombic Ti2O3, which is confirmed by X-ray magnetic circular dichroism measurements. Using first-principles calculations, the ferromagnetism is attributed to a particular type of oxygen vacancies in the orthorhombic Ti2O3. The room-temperature ferromagnetism observed in orthorhombic-structured Ti2O3, demonstrates a new route toward controlling magnetism in epitaxial oxide films through selective stabilization of polymorph phases.