  So far, magneto-ionics, understood as voltage-driven ion transport in
magnetic materials, has largely relied on controlled migration of oxygen
ion/vacancy and, to a lesser extent, lithium and hydrogen. Here, we demonstrate
efficient, room-temperature, voltage-driven nitrogen transport (i.e., nitrogen
magneto-ionics) by electrolyte-gating of a single CoN film (without an
ion-reservoir layer). Nitrogen magneto-ionics in CoN is compared to oxygen
magneto-ionics in Co3O4, both layers showing a nanocrystalline
face-centered-cubic structure and reversible voltage-driven ON-OFF
ferromagnetism. In contrast to oxygen, nitrogen transport occurs uniformly
creating a plane-wave-like migration front, without assistance of diffusion
channels. Nitrogen magneto-ionics requires lower threshold voltages and
exhibits enhanced rates and cyclability. This is due to the lower activation
energy for ion diffusion and the lower electronegativity of nitrogen compared
to oxygen. These results are appealing for the use of magneto-ionics in nitride
semiconductor devices, in applications requiring endurance and moderate speeds
of operation, such as brain-inspired computing.
