The magnetic order of antiferromagnetic Mn3NiN thin films under biaxial strain*

We explore the magnetic phase diagram of piezomagnetic antiperovskite Mn₃NiN thin films grown on different substrates as a function of the induced biaxial strain using magnetotransport and neutron scattering. We find that the anomalous Hall effect is an effective probe of the out-of-plane-magnetisation in our films. Under compressive in-plane biaxial strain, the films support a canted antiferromagnetic (AFM) state with large coercivity at low temperature that transformed at a well-defined Neel transition temperature into a soft ferrimagnetic-like (FIM) state at high temperatures. In stark contrast, under tensile strain the magnetisation value decreases rapidly above the Neel transition. The resulting magnetic phase diagram shares many characteristics with that predicted for thin films of the closely related antiperovskite Mn₃GaN.