Lee Changmin, Vir Praveen, Manna Kaustuv, Shekhar Chandra, Moore J E, Kastner M A, Felser Claudia, Orenstein Joseph
Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
Max Planck Institute for Chemical Physics of Solids, Dresden, Germany.
Nat Commun. 2022 May 30;13(1):3000. doi: 10.1038/s41467-022-30460-y.
The ferromagnetic phase of CoSnS is widely considered to be a topological Weyl semimetal, with evidence for momentum-space monopoles of Berry curvature from transport and spectroscopic probes. As the bandstructure is highly sensitive to the magnetic order, attention has focused on anomalies in magnetization, susceptibility and transport measurements that are seen well below the Curie temperature, leading to speculation that a "hidden" phase coexists with ferromagnetism. Here we report spatially-resolved measurements by Kerr effect microscopy that identify this phase. We find that the anomalies coincide with a deep minimum in domain wall (DW) mobility, indicating a crossover between two regimes of DW propagation. We demonstrate that this crossover is a manifestation of a 2D phase transition that occurs within the DW, in which the magnetization texture changes from continuous rotation to unidirectional variation. We propose that the existence of this 2D transition deep within the ferromagnetic state of the bulk is a consequence of a giant quality factor for magnetocrystalline anisotropy unique to this compound. This work broadens the horizon of the conventional binary classification of DWs into Bloch and Néel walls, and suggests new strategies for manipulation of domain walls and their role in electron and spin transport.
CoSnS的铁磁相被广泛认为是一种拓扑外尔半金属，输运和光谱探测为贝里曲率的动量空间单极子提供了证据。由于能带结构对磁序高度敏感，人们的注意力集中在居里温度以下显著出现的磁化、磁化率和输运测量异常现象上，这引发了一种推测，即一种“隐藏”相与铁磁性共存。在此，我们报告了通过克尔效应显微镜进行的空间分辨测量，从而确定了这个相。我们发现这些异常现象与畴壁（DW）迁移率的一个深度最小值相吻合，这表明DW传播的两种机制之间存在转变。我们证明这种转变是DW内发生的二维相变的一种表现，其中磁化纹理从连续旋转变为单向变化。我们提出，在块体铁磁态深处存在这种二维转变是该化合物独特的磁晶各向异性的巨大品质因数的结果。这项工作拓宽了将DW传统二元分类为布洛赫壁和尼尔壁的视野，并为畴壁的操纵及其在电子和自旋输运中的作用提出了新策略。
