论文标题
部分可观测时空混沌系统的无模型预测
Bragg diffraction by a magnetic all-in-all-out configuration with application to a cubic cerium pyrochlore oxide
论文作者
论文摘要
中子和X射线的Bragg衍射非常适合确定晶体中磁化分布的任务。这两种技术的应用是通过将观察到的强度与特定模型计算的强度进行对比的,并根据需要更改模型以实现令人满意的一致性。例如,在pyrochlore氧化物的背景下,经常提到与立方面部面部晶格上磁性偶极子的磁性偶构的(AIAO)磁性构型,但似乎尚未计算相应的中子和X射线衍射模式。我们从磁性空间组定义的AIAO磁性构型的Bragg点模式的结果是对称性的,并产生精确的反射条件。具体而言,在我们的模型中,禁止磁性偶极子的远程顺序。散装特性来自包括四倍体和八杆的高阶多物。已经发现了排除所有磁多磁多物以外的所有磁多物的布拉格斑点,并且可以通过中子衍射和谐振X射线衍射可以观察到它们。葡萄离子(4F1)允许的所有磁多物都以据可查且异常的磁接地状态的系数表示。立方结构中铜位的对称性限制了系数。例如,我们的散射幅度在CE2ZR2O7上的中子和X射线衍射实验中都有应用,并搜索了众所周知的Octupole。还提供了供将来使用的结果,这是粉末样品的总能量积分中子散射强度的结果。
The Bragg diffraction of neutrons and x-rays are well-suited to the task of determining the distribution of magnetization in crystals. Applications of the two techniques proceed by contrasting observed intensities with intensities calculated with a specific model, and changing the model as need be to achieve satisfactory agreement. An all-in-all-out (AIAO) magnetic configuration of magnetic dipoles on a cubic face-centred lattice with networks of corner-sharing tetrahedra is often mentioned in the context of pyrochlore oxides, for example, but the corresponding neutron and x-ray diffraction patterns appear not have been calculated. Our results for patterns of Bragg spots from an AIAO magnetic configuration defined by a magnetic space group are symmetry informed and yield exact reflection conditions. Specifically, a long-range order of magnetic dipoles is forbidden in our model. Bulk properties arise from higher-order multipoles that include quadrupoles and octupoles. Bragg spots that exclude all magnetic multipoles other than an octupole have been discovered, and they can be observed by both neutron diffraction and resonant x-ray diffraction. All magnetic multipoles allowed in diffraction by cerium ions (4f1) are presented in terms of coefficients in a well-documented and unusual magnetic ground state. Symmetry of the cerium site in the cubic structure constrains the coefficients. Our scattering amplitudes have an application in both neutron and x-ray diffraction experiments on Ce2Zr2O7, for example, and searches for the sought-after cerium octupole. Also presented for future use is a result for the total, energy-integrated magnetic neutron scattering intensity by a powder sample.