ABSTRACT
Spin-transfer torque (STT) and spin-orbit torque (SOT) are spintronic phenomena allowing magnetization manipulation using electrical currents. Beyond their fundamental interest, they allow developing new classes of magnetic memories and logic devices, in particular based on domain wall (DW) motion. In this work, we report the study of STT-driven DW motion in ferrimagnetic manganese nickel nitride (Mn4-xNixN) films, in which magnetization and angular momentum compensation can be obtained by the fine adjustment of the Ni content. Large domain wall velocities, approaching 3000 m/s, are measured for Ni compositions close to the angular momentum compensation point. The reversal of the DW motion direction, observed when the compensation composition is crossed, is related to the change of direction of the angular momentum with respect to that of the spin polarization. This is confirmed by the results of ab initio band structure calculations.
ABSTRACT
Spintronics, which is the basis of a low-power, beyond-CMOS technology for computational and memory devices, remains up to now entirely based on critical materials such as Co, heavy metals and rare-earths. Here, we show that Mn4N, a rare-earth free ferrimagnet made of abundant elements, is an exciting candidate for the development of sustainable spintronics devices. Mn4N thin films grown epitaxially on SrTiO3 substrates possess remarkable properties, such as a perpendicular magnetization, a very high extraordinary Hall angle (2%) and smooth domain walls at the millimeter scale. Moreover, domain walls can be moved at record speeds by spin-polarized currents, in absence of spin-orbit torques. This can be explained by the large efficiency of the adiabatic spin transfer torque, due to the conjunction of a reduced magnetization and a large spin polarization. Finally, we show that the application of gate voltages through the SrTiO3 substrates allows modulating the Mn4N coercive field with a large efficiency.
