Voltage-driven motion of nitrogen ions: a new paradigm for magneto-ionics

Abstract

<jats:title>Abstract</jats:title> <jats:p>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.</jats:p>

Roadmap on Magnetoelectric Materials and Devices

“…Besides strain and electric surface charging, applied electric fields can also induce changes in the oxidation state of magnetic metallic alloys or semiconductors (i.e., reduction/oxidation reactions or ion migration), particularly when they are immersed in liquid electrolytes or grown adjacent to ionically conducting buffer layers (solid electrolytes) [11,12,[324][325][326][327][328][329][330][331][332][333][334][335]. Electric-field-induced oxygen motion in magnetic materials has recently revolutionized voltage control of magnetism since this mechanism may allow for an unprecedented modulation of magnetic properties (MS, HC) in either permanent or temporary ways (if effects are reversible upon application of voltage of opposite polarity) [326,329,333,[336][337][338].…”

“…The properties of FM or ferrimagnetic oxides have also been tuned by voltage-driven lithiation (Li + incorporation using suitable electrolytes) [345][346][347][348]. Recent works have also reported magneto-ionic effects arising from fluor [349] or nitrogen [334] ion migration. Nitrogen magneto-ionics offers some advantages with respect to oxygen magneto-ionics in terms of operation speed, threshold voltages to induce the ME effects and improved cyclability [334].…”

“…Recent works have also reported magneto-ionic effects arising from fluor [349] or nitrogen [334] ion migration. Nitrogen magneto-ionics offers some advantages with respect to oxygen magneto-ionics in terms of operation speed, threshold voltages to induce the ME effects and improved cyclability [334].…”

Reversible writing/deleting of magnetic skyrmions through hydrogen adsorption/desorption

“…On the other hand, chemisorption of hydrogen or oxygen on metal surfaces, limited to surface adsorption without penetrating into the metal interior [28], has been shown to induce DMI [29,30] and allow the tuning of magnetic anisotropy [31]. Understanding adsorbate induced magnetic properties is particularly relevant to the emerging eld of magneto-ionics, where oxygen, hydrogen, or nitrogen ions can be driven to/from interfaces via electric elds, enabling the reversible tuning of magnetic properties such as magnetic anisotropy and magnetization [32][33][34][35][36]. Combining the exciting promise of skyrmion-based spintronics and the eld of light element-based magneto-ionics motivates the search for ways to control skyrmion properties through chemisorption.…”

Magneto-ionic suppression of magnetic vortices

“…43 Among all converse ME effects, magneto-ionics is gaining attention because voltage-driven ion transport between the magnetic material of interest and an ion source/sink allows for a stringent non-volatile control of interfacial magnetism to an unprecedented extent. [25,48,49] Upon electrolyte gating, the ions may form diffusion channels or even uniform migration fronts (eventually developing new interfaces within the actuated films), resulting in unique magnetic characteristics (in e.g., oxides or nitrides). [25,48] Magneto-ionic effects can involve the transport of various types of ion species, such as alkali metal cations (Li .…”