Transition metal nitrides and their mixed crystals for spintronics

Anti-perovskite transition metal nitrides exhibit a variety of magnetic properties - such as ferromagnetic, ferrimagnetic, and paramagnetic - depending on the 3d transition metal. Fe4N and Co4N are ferromagnetic at room temperature (RT), and the minority spins play a dominant role in the electrical transport properties. However, Mn4N is ferrimagnetic at RT and exhibits a perpendicular magnetic anisotropy caused by tensile strain. Around the magnetic compensation in Mn4N induced by impurity doping, researchers have demonstrated ultrafast current-induced domain wall motion reaching 3000 m s-1 at RT, making switching energies lower and switching speed higher compared with Mn4N. In this review article, we start with individual magnetic nitrides - such as Fe4N, Co4N, Ni4N, and Mn4N; describe the nitrides' features; and then discuss compounds such as Fe4-x A x N (A = Co, Ni, and Mn) and Mn4-x B x N (B = Ni, Co, and Fe) to evaluate nitride properties from the standpoint of spintronics applications. We pay particular attention to preferential sites of A and B atoms in these compounds, based on x-ray absorption spectroscopy and x-ray magnetic circular dichroism.