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 3dtransition 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^-1at 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 Fe_4-AN (A = Co, Ni, and Mn) and Mn_4-BN (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.