Polarized neutron diffraction (PND) is a powerful technique to distinguish a weak magnetic contribution from the total scattering intensity. It can provide a detailed insight into the microscopic spin ordering at the unit cell level, but also into the mesoscopic magnetic ordering, like different types of domain populations. Here we report on the application of this technique to the long-standing problem of determining the absolute direction of the Dzyaloshinskii-Moriya vector in relation to the crystal structure. The proposed PND method, based on the measurement of one representative reflection, is easy to perform and straightforward to interpret. The absolute sign of the Dzyaloshinskii-Moriya interaction (DMI) in ${\mathrm{MnCO}}_3$ has been independently determined by PND and found to be in agreement with recent results obtained by resonant magnetic synchrotron scattering. This validates the method. In addition, the absolute DMI vector direction in the prototypical room-temperature weak ferromagnet $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ (hematite) has been determined for the first time. To demonstrate the generality of our method, further examples with different symmetries are also presented. Ab initio calculations of the resulting weak noncollinear magnetization using the quantum espresso package, considering DMI in addition to the symmetric magnetic exchange interaction, were also conducted and found to be in agreement with the experimental results from PND.

中文翻译：

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极化中子揭示典型弱铁磁体中Dzyaloshinskii-Moriya相互作用的绝对方向

极化中子衍射（PND）是一种有力的技术，可从总散射强度中区分出弱磁性。它可以提供对单位细胞水平上微观自旋排序的详细了解，也可以深入了解介观磁排序（如不同类型的域种群）。在这里，我们报告了该技术在确定Dzyaloshinskii-Moriya矢量相对于晶体结构的绝对方向的长期问题上的应用。基于一种代表性反射的测量，所提出的PND方法易于执行且易于解释。Dzyaloshinskii-Moriya相互作用（DMI）在${\mathrm{碳酸锰}}_3$PND由PND独立确定，发现与共振磁同步加速器散射获得的最新结果一致。这验证了该方法。此外，典型的室温弱铁磁体中的DMI绝对矢量方向$\alpha \text{-}{铁}_{\mathrm{2个}}{\mathrm{Ø}}_3$（赤铁矿）首次确定。为了证明我们方法的通用性，还介绍了具有不同对称性的其他示例。还进行了使用量子浓缩咖啡包装，并考虑了DMI和对称磁交换相互作用的情况下，产生的弱非共线磁化强度的从头算计算，发现与PND的实验结果相符。