Abstract
Magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. Here, we demonstrate room-temperature voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a CoN film. Nitrogen magneto-ionics in CoN is compared to oxygen magneto-ionics in Co3O4. Both materials are nanocrystalline (face-centered cubic structure) and show 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. Remarkably, 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 may open new avenues in applications such as brain-inspired computing or iontronics in general.
Highlights
Magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions
Magneto-ionic systems comprise layered heterostructures built around a ferromagnetic target material, such as Co or Fe, grown adjacent to solid-state electrolyte films (e.g., GdOx2 or HfO226)
Our work demonstrates robust room-temperature nitrogen magneto-ionics in CoN
Summary
Magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. 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. Magneto-ionics using structural oxygen (i.e., oxygen incorporated in the crystallographic structure of the actuated material) exhibits outstanding stability and reversibility[7,8] This has been demonstrated in electrolytegated[20,29,30,31,32,33], thick (≥100 nm) paramagnetic Co3O4 films, in which room-temperature voltage-controlled ON-OFF ferromagnetism has been achieved, benefiting from defect-assisted voltage-driven transport of structural oxygen. CoN and Co3O4 single-layer films are voltage-actuated to compare nitrogen vs oxygen magnetoionic performances These materials were selected since they both exhibit voltage-induced ON-OFF ferromagnetic transitions. Controlled motion of nitrogen ions with voltage might enable the use of magneto-ionics in new technological areas that require endurance and moderate operation speeds (e.g., neuromorphic computing[34] or micro-electro-mechanical systems[35])
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