Ba替代诱导磁性Weyl半金属EuCd $_2$ As $_2$自旋倾斜的证据
Evidence of Ba substitution induced spin-canting in the magnetic Weyl semimetal EuCd$_2$As$_2$
摘要：
最近，EuCd $_2$ As $_2$被预测为磁性Weyl半金属，具有由A型反铁磁性产生的孤对Weyl节点，并受到旋转对称性的保护。然而，很快就发现实际的磁性结构打破了旋转对称性，内部压力后来被认为是稳定所需磁性状态的途径。在这项工作中，我们通过合成一系列的Eu $_{1-x}$ Ba $_x$ Cd $_2$ As $_2$单晶，并通过实验技术和第一性原理计算研究它们的结构，磁性和输运性质来验证这一预测。我们发现，小浓度的Ba（$\sim 3-10\% $）导致一个小的面外倾斜的Eu时刻。然而，对于更高的浓度，这种效果被抑制，几乎在平面模型被恢复。研究的输运性质，我们发现，所有的组合物显示的异常霍尔效应的内在机制，以及在纵向通道中的大的负磁阻为主的证据。输运性质的非单调演变被视为整个系列相关的建议倾斜倾斜可能会提高拓扑效应。仔细的密度泛函理论计算，使用全电子的方法修改以前的预测，发现一个纯铁磁基态与面内时刻的EuCd $_2$作为$_2$和Eu $_{0.5}$ Ba $_{0.5}$ Cd $_2$作为$_2$化合物-证实了我们的实验结果。这项工作表明，Ba取代可以调整的磁性在意想不到的方式，相关的拓扑性质的措施的变化，鼓励未来的工作，以找到理想的Ba浓度Eu矩倾斜。
英文摘要：
Recently EuCd$_2$As$_2$ was predicted to be a magnetic Weyl semi-metal with a lone pair of Weyl nodes generated by A-type antiferromagnetism and protected by a rotational symmetry. However, it was soon discovered that the actual magnetic structure broke the rotational symmetry and internal pressure was later suggested as a route to stabilize the desired magnetic state. In this work we test this prediction by synthesizing a series of Eu$_{1-x}$Ba$_x$Cd$_2$As$_2$ single crystals and studying their structural, magnetic and transport properties via both experimental techniques and first-principles calculations. We find that small concentrations of Ba ($\sim 3-10\% $) lead to a small out-of-plane canting of the Eu moment. However, for higher concentrations this effect is suppressed and a nearly in-plane model is recovered. Studying the transport properties we find that all compositions show evidence of an Anomalous Hall Effect dominated by the intrinsic mechanism as well as large negative magnetoresistances in the longitudinal channel. A non-monotonic evolution of the transport properties is seen across the series which correlates to the proposed canting suggesting canting may enhance the topological effects. Careful density functional theory calculations using an all-electron approach revise prior predictions finding a purely ferromagnetic ground state with in-plane moments for both the EuCd$_2$As$_2$ and Eu$_{0.5}$Ba$_{0.5}$Cd$_2$As$_2$ compounds - corroborating our experimental findings. This work suggests that Ba substitution can tune the magnetic properties in unexpected ways which correlate to changes in measures of topological properties, encouraging future work to locate the ideal Ba concentration for Eu moment canting.
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