Experimental study of topological properties in chiral antiferromagnets

1.在室温下，我们在反铁磁性金属Mn3Sn中发现了很大的压磁效应。在某种类型的反铁磁体中，应变和磁化之间的线性耦合是允许的，这种耦合被称为“压磁”，如果这种效应在室温下很大，那么这种耦合在技术上是有意义的。我们发现，通过这种压磁效应，0.1%的应变可以控制Mn3Sn霍尔信号的大小和符号，这是以前在反铁磁体中没有看到的效果。我们与UBC的Dasgupta博士和Johns Hopkins大学的Tschernyshov教授合作，他们能够构建一个朗道理论，可以在同一框架下解释压磁效应和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原子力显微镜Mn3Sn磁相图，它是Mn浓度的函数。我们成功地在0.009&lt；x&lt；0.1%范围内生长了Mn3+xSn1-x单晶。我们发现原始的Mn3Sn的基态是一个无公度磁序，在T=280K通过一级相变从三角形反手征相中分离出来。通过磁测量和输运测量，我们发现掺入的Mn强烈地抑制了无公度相，有利于三角形反手征相，但在较低的温度下会导致玻璃状铁磁相的出现。这项工作将对薄膜Mn3Sn的发展具有重要意义，Mn3Sn3是一种最近在自旋电子学领域引起极大关注的材料。

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.