Neptunium octupole and hexadecapole motifs in NpO2 directly from electric dipole (E1) enhanced x-ray Bragg diffraction
Neptunium octupole and hexadecapole motifs in NpO2 directly from electric dipole (E1) enhanced x-ray Bragg diffraction
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NpO2 中的镎八极和十六极图案直接来自电偶极子 (E1) 增强的 X 射线布拉格衍射
DOI：
10.1088/0953-8984/15/26/301
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
U. Staub
中科院分区：
文献类型：
--
作者：
S. Lovesey;E. Balcar;C. Detlefs;G. Laan;D. Sivia;U. Staub
的相变在NPO 2在T0？25.5 ? K伴随着X射线布拉格衍射图案中的超晶格反射的开始，其强度通过电偶极子（E1）事件增强。使用其他技术的额外的实验表明，在T0的Np磁矩没有秩序。在12 K下的超晶格强度的偏振分析的结果符合T0以下的远程磁秩序的情况下，观察到的信号在两个未旋转（？'?)旋转（？'?)散射通道，而磁（偶极）矩将仅在旋转通道中起作用。我们表明，这些经验的发现，连同一个狭窄的能量分布的布拉格强度在NP？M4边缘，是一致的磁性和电荷的贡献E1布拉格幅度所描述的Np 5 f多极的秩3（八极）和4（十六极）。关键我们的理解的X射线衍射数据收集在附近的NP？M4边缘是创建3d 3/2核心级结构的交换场的识别。特别重要的交流领域在NP？M4边缘是着重揭示在计算相应的X射线吸收谱与不核心？价相互作用从有关NpO 2的实验信息，我们可以推断出一个基态波函数的NP？5 f3价层，并估计八极和十六极的饱和值。我们导致零值为Np多极秩2（四极）和5（triakontadipole）。
The phase transition in NpO2 at T0 ? 25.5 ?K is accompanied by the onset of superlattice reflections in the x-ray Bragg diffraction pattern, with intensity enhanced by an electric dipole (E1) event. Additional experiments using other techniques indicate no ordering at T0 of Np magnetic moments. Absence of long-range magnetic order below T0 fits with the outcome of a polarization analysis of superlattice intensities at 12 K; signals are observed in both the unrotated (?'?) and rotated (?'?) channels of scattering while magnetic (dipole) moments would contribute only in the rotated channel. We demonstrate that these empirical findings, together with a narrow energy profile of the Bragg intensity at the Np?M4 edge, are consistent with magnetic and charge contributions to the E1 Bragg amplitude described by Np 5f multipoles of ranks 3 (octupole) and 4 (hexadecapole). Key to our understanding of the x-ray diffraction data gathered in the vicinity of the Np?M4 edge is recognition of an exchange field creating 3d3/2 core-level structure. The particular importance of the exchange field at the Np?M4 edge is emphatically revealed in calculations of the corresponding x-ray absorption spectrum with and without the core?valence interaction. From the experimental information about NpO2 we can infer a ground-state wavefunction for the Np?5f3 valence shell and estimate saturation values for the octupole and hexadecapole. We are led to null values for Np multipoles of ranks 2 (quadrupole) and 5 (triakontadipole).