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–x
Ni
x
N) 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.
The ferrimagnet Mn4N forms a family of compounds useful in spintronics. In a compound comprising non-magnetic and magnetic elements, one basically expects the compound to become ferromagnetic when the proportion of the magnetic element increases. Conversely, one does not expect ferromagnetism when the proportion of the non-magnetic element increases. Surprisingly, Mn4N becomes ferromagnetic at room temperature when the Mn content is decreased by the addition of In atoms, a non-magnetic element. X-ray magnetic circular dichroism measurement reveals that the magnetic moment of Mn atoms at face-centered sites, Mn(II), reverses between x = 0.15 and 0.27 and aligns parallel to that of Mn atoms at corner sites, Mn(I), at x = 0.27 and 0.41. The sign of the anomalous Hall resistivity also changes between x = 0.15 and 0.27 in accordance with the reversal of the magnetic moment of the Mn(II) atoms. These results are interpreted from first-principles calculation that the magnetic moment of Mn(II) sites which are the nearest neighbors to the In atom align to that of Mn(I) sites.
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