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 Fe4-xAxN (A = Co, Ni, and Mn) and Mn4-xBxN (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.

Micromagnetics simulation for magnetization switching of permalloy films with pure spin current injection.

Pure spin current injection has recently been developed as an effective method of controlling magnetization in spintronic devices. In order to investigate the dynamics of the magnetization reversal process in magnetic films with pure spin current injection, we performed micromagnetics simulations based on the Landau-Lifshitz equation and taking into account a term representing spin transfer torque caused by the pure spin current. We studied the time evolution of magnetization in permalloy films and estimated the probability of magnetization switching to show how the probability depends on the width of the film and the intensity of the injected spin current. We found that, in narrow films, a transverse domain wall is formed in the film and that this wall moves outside the film when magnetization switching occurs. The switching time becomes shorter as the intensity of the injected spin current is increased. In wide films, on the other hand, magnetization switching does not occur even if the intensity of injected spin current is increased. In such cases, either a magnetic vortex core is formed or the configuration of the moments hardly changes from the initial magnetic state.