Metallic Nitride and Carbide Perovskites: History and Prospects

Energy-level diagrams for cubic metallic Fe₄N and Mn₄N were proposed by Goodenough in the late 1960s. Fe₄N is ferromagnetic, but Mn₄N is ferrimagnetic with a large moment on Mn^c at the cube corner site and a much smaller antiparallel contribution from Mn^f at the three face-centre sites. Neutron diffraction revealed noncollinear ferrimagnetism with no compensation where the Mn^f moments form 120° triangular antiferromagnetic sublattices but are tilted out of the kagome (111) planes to give the small net sublattice moment. A rich variety of magnetic ordering exists in the ternary Mn_3−xM′_xN metallic perovskites. Partial substitution of nonmagnetic M′ on Mn^c sites leads to a tunable ferrimagnetic compensation point. Two possible antiferromagnetic modes in the kagome planes are a topological Γ^4g mode, and a nontopological Γ^5g mode where the in-plane components of the Mn^f spins lie, respectively, perpendicular and parallel to the edges if the triangles in the kagome planes . Interest in the metallic perovskites has revived with the availability of high-quality thin films that facilitate measurements of magneto-transport properties, strain effects and spin wave velocity. The range of magnetic structures, magnetotransport, magnetocaloric and magnetovolume effects is exceptionally large. The topological ferrimagnets exhibit large anomalous Hall effects. The magnetism is compared with materials where N is replaced by C.