Experimental study of topological properties in chiral antiferromagnets

1. 我们发现反铁磁金属Mn3Sn在室温下具有较大的压磁效应。在某一类反铁磁体中，应变和磁化之间的线性耦合是允许的，被称为“压磁性”，如果在室温下效果很大，则可以在技术上相关。我们发现，通过这种压磁性，0.1%左右的应变可以控制Mn3Sn中霍尔信号的大小和符号，这是以前在反铁磁体中未见过的效果。我们与英国哥伦比亚大学的Dasgupta博士和约翰霍普金斯大学的Tschernyshov教授合作，建立了一个朗道理论，可以在同一框架内解释压磁效应和AHE信号的调制。这项工作已被《自然物理》杂志接受。我们首次建立了三角形AFM Mn3Sn的磁相图，该磁相图是Mn浓度的函数。我们成功地在0.009 < x < 0.1范围内生长出了Mn3+xSn1-x单晶。我们发现原始Mn3Sn的基态是一个不相称的磁阶，在T=280 K时通过一阶跃迁与三角形反手性相分离。通过磁强计和输运测量，我们发现掺杂Mn强烈抑制了不匹配相，有利于三角形反手性相，但在较低温度下导致玻璃铁磁相的出现。这项工作将对薄膜Mn3Sn的发展具有重要意义，这是一种最近在自旋电子学界备受关注的材料。

1. We found a large piezomagnetic effect in an antiferromagnetic metal Mn3Sn at room temperature. In a certain class of antiferromagnets, a linear coupling between strain and magnetization is allowed and is known as “piezomagnetism”, which can be technologically relevant if the effect is large at room temperature. We found that through this piezomagnetism, a strain in the order of 0.1% can control the magnitude and sign of the Hall signal in Mn3Sn, an effect not previously seen in antiferromagnets. We collaborated with Dr. Dasgupta from UBC and Prof. Tschernyshov from Johns Hopkins University, and they were able to construct a Landau theory which can explain the piezomagnetic effect and the modulation of the AHE signal in the same framework. This work has been accepted into Nature Physics.2. We established the magnetic phase diagram of triangular AFM Mn3Sn as a function of Mn concentration for the first time. We successfully grew Mn3+xSn1-x single crystals within the range 0.009 < x < 0.1. We found that the ground state of a pristine Mn3Sn is an incommensurate magnetic order, which is separated from the triangular antichiral phase by a first-order transition at T=280 K. Through magnetometry and transport measurements, we show that doping Mn strongly suppresses the incommensurate phase in favor of the triangular antichiral phase but leads to the appearance of a glassy ferromagnetic phase at lower temperatures. This work will be important in the development of thin film Mn3Sn, which is a material that has recently gained much attention in the spintronics community.