The structure-function relationship in non-collinear Mn3NiN multilayers

Non-collinear antiferromagnets (nc-AFM) have been recognised as an ideal platform for future computing technologies due to their enhanced electrical, thermal and optical effects. This is because they possess non-trivial topologies in their electronic band structure which allows for intrinsic properties normally associated with ferromagnets, despite possessing an orders-of-magnitude smaller magnetisation. Mn3NiN is highly sensitive to strain, and we have demonstrated that it leads to a small net magnetic moment. More recently, we have used transmission electron microscopy (TEM) to reveal the impact of local strain, caused by edge dislocation defects within the film. These defects create a region, ~20 nm thick, close to the film/substrate interface with very high local strains (up to +/-8%) and are expected to lead to a large magnetic moment in this region, which will impact the intrinsic properties of the film. By annealing, we can cause these dislocations to migrate and concentrate into a regular array 2 nm region at the interface. Beyond this, the Mn3NiN thin films are highly coherent and relaxed. These annealed films show a reduced defect density, and a reduced magnetisation as measured using SQUID magnetometry. Polarised neutron reflectivity (PNR) is an essential technique to investigate these effects as it can provide a depth profile of the magnetic properties, giving us further evidence how the structural inhomogeneities at interfaces impact the magnetism.