Magnetic Structure of the Weyl Semi-Metal Mn_3Ge

In recent years attention has been drawn to exploiting the physics of new materials which exhibit dissipation-less quantum states. Exemplars or such materials are the non-collinear antiferromagnetic Weyl semi-metals such as Mn_3Ge. The presence of Weyl points and spin-orbit coupling induced gaps in Mn_3Ge, and cousin systems has been found to lead to a large anomalous Hall effect, despite absence of a sizeable ferromagnetic order. We propose a polarized neutron reflectivity study of thin film samples of Mn_3Ge. In our studies to date we see evidence that the surfaces of our films have a remnant ferromagnetism although the bulk is antiferromagnetic and that there is a strong temperature dependence to the magnetisation. We wish to measure and understand the magnetisation profile in our thin films at temperatures below room temperature with the eventual aim of exploiting the topological states at interfaces with other material systems.