Analysis of charge and orbital order in Fe3O4 by Fe L2,3 resonant x-ray diffraction
Analysis of charge and orbital order in Fe3O4 by Fe L2,3 resonant x-ray diffraction
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DOI：
10.1103/physrevb.88.195110
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发表时间：
2013-11-06
影响因子：
3.7
通讯作者：
Schuessler-Langeheine, C.
中科院分区：
文献类型：
--
作者：
Tanaka, A.;Chang, C. F.;Schuessler-Langeheine, C.
为了阐明125K的Verwey转变温度T-V以下的电荷和轨道有序性，用软X射线衍射法在Fe-L-2，L-3共振处研究了在阶梯状的MgO(001)衬底上生长的部分缠绕的磁铁矿薄层。测量了(001/2)(C)和(001)(C)反射强度的方位角、入射光子偏振度和能量依赖关系，并用组态相互作用FeO6团簇模型进行了分析。(001/2)(C)反射强度与方位角的关系直接反映了轨道在初始状态下的空间群对称性，而不是通过有序引起的晶格扭曲引起的中态能级移动间接地表示轨道的空间群对称性。通过对(0 0 1 2)c反射强度的分析，证明了T-V以下B位的t2g轨道有较大的单斜形变，Re[F-xy]/Re[F-Yz]接近于2.这一发现与目前提出的大多数Verwey跃迁理论相矛盾.我们发现，实验观察到的共振光谱不能用最近的LDA+U和GGA+U能带结构计算得到的轨道和电荷顺序来解释，而是用复数轨道顺序来解释，并与很好地一致。
To elucidate charge and orbital order below the Verwey transition temperature T-V similar to 125 K, a thin layer of magnetite partially detwined by growth on the steppedMgO(001) substrate has been studied by means of soft x-ray diffraction at the Fe L-2,L-3 resonance. The azimuth angle, incident photon polarization, and energy dependence of the (001/2)(c) and (001)(c) reflection intensities have been measured, and analyzed using a configuration-interaction FeO6 cluster model. The azimuth dependence of the (001/2)(c) reflection intensities directly represents the space-group symmetry of the orbital order in the initial state rather than indirectly through the intermediate-state level shifts caused by the order-induced lattice distortions. From the analysis of the (00 1 2) c reflection intensities, the orbital order in the t2g orbitals of B sites below T-V is proved to have a large monoclinic deformation with the value of Re[F-xy]/Re[F-yz] similar to 2. This finding contradicts the majority of theories on the Verwey transition so far proposed. We show that the experimentally observed resonance spectra cannot be explained by orbital and charge orders obtained with recent LDA+ U and GGA+ U band structure calculations but by a complex-number orbital order with excellent agreement.