Sign reversal in anomalous Hall effect at two Sn compositions in Mn4-xSnxN films on MgO(001) substrates

Rare-earth-free Mn4N has attracted increasing attention as a spintronic material thanks to its ferrimagnetism, perpendicular magnetic anisotropy, and controllability of magnetic properties by partial replacement of Mn atoms with other elements. Here, we grew & SIM;25-nm-thick Mn4-xSnxN epitaxial films (x = 0-1.4) on MgO(001) substrates by molecular beam epitaxy and investigated their lattice constants and magneto-transport properties. The ratio of the out-of-plane lattice constant c to the in-plane lattice constant a in the Mn4-xSnxN films, c/a, was less than 1 for x < 0.9, but it changed to more than 1 for x = 1.0. Amazingly, the sign of the anomalous Hall effect changed twice with increasing x. These results suggest that the magnetic structure of the Mn4-xSnxN films varies with Sn composition. Possible mechanisms of the magnetic structure change include magnetic compensation, ferrimagnetic-ferromagnetic phase transition, and the formation of noncollinear magnetic structures.