Spin-orbit coupling and crystal-field distortions for a low-spin 3d5 state in BaCoO3
Spin-orbit coupling and crystal-field distortions for a low-spin 3d5 state in BaCoO3
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DOI：
10.1103/physrevb.100.205139
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发表时间：
2019-11-26
影响因子：
3.7
通讯作者：
Tjeng, L. H.
中科院分区：
文献类型：
--
作者：
Chin, Y. Y.;Hu, Z.;Tjeng, L. H.
我们利用软x射线吸收光谱在col -2，L-3和ok边缘，磁圆二色性在col -2，L-3边缘和价带硬x射线光电子能谱研究了BaCoO3的电子结构。光谱定量分析表明，Co离子处于形式的低自旋四价3d(5)态，体系为负电荷转移Mott绝缘体。自旋轨道耦合对系统的磁性也起着重要的作用。同时，存在一个三角晶体场，其强度足以使3d(5)离子远离J(eff)= 1/2态。这个晶体场的标志是a（1g）轨道被双重占据，这解释了在这个由面共享的CoO6八面体链组成的体系中没有佩尔斯跃迁。此外，在e(g)（pi）中有一个空穴，可以理解轨道矩和强磁晶各向异性的存在。然而，我们还推断，必须存在较低对称性的晶体场才能定量地再现所测量的轨道矩，从而表明BaCoO3中可能发生轨道有序。
We have studied the electronic structure of BaCoO3 using soft x-ray absorption spectroscopy at the Co L-2,L-3 and O K edges, magnetic circular dichroism at the Co L-2,L-3 edges, and valence band hard x-ray photoelectron spectroscopy. The quantitative analysis of the spectra established that the Co ions are in the formal low-spin tetravalent 3d(5) state and that the system is a negative charge transfer Mott insulator. The spin-orbit coupling also plays an important role for the magnetism of the system. At the same time, a trigonal crystal field is present with sufficient strength to bring the 3d(5) ion away from the J(eff )= 1/2 state. The sign of this crystal field is such that the a(1g) orbital is doubly occupied, explaining the absence of a Peierls transition in this system, which consists of chains of face-sharing CoO6 octahedra. Moreover, with one hole residing in e(g)(pi), the presence of an orbital moment and strong magnetocrystalline anisotropy can be understood. Yet we also infer that crystal fields with lower symmetry must be present to reproduce the measured orbital moment quantitatively, thereby suggesting the possibility for orbital ordering to occur in BaCoO3.