Abstract
Magneto-ionics allows for tunable control of magnetism by voltage-driven transport of ions, traditionally oxygen or lithium and, more recently, hydrogen, fluorine, or nitrogen. Here, magneto-ionic effects in single-layer iron nitride films are demonstrated, and their performance is evaluated at room temperature and compared with previously studied cobalt nitrides. Iron nitrides require increased activation energy and, under high bias, exhibit more modest rates of magneto-ionic motion than cobalt nitrides. Ab initio calculations reveal that, based on the atomic bonding strength, the critical field required to induce nitrogen-ion motion is higher in iron nitrides (≈6.6 V nm–1) than in cobalt nitrides (≈5.3 V nm–1). Nonetheless, under large bias (i.e., well above the magneto-ionic onset and, thus, when magneto-ionics is fully activated), iron nitride films exhibit enhanced coercivity and larger generated saturation magnetization, surpassing many of the features of cobalt nitrides. The microstructural effects responsible for these enhanced magneto-ionic effects are discussed. These results open up the potential integration of magneto-ionics in existing nitride semiconductor materials in view of advanced memory system architectures.
Highlights
Modern electronic devices store data using electric current to manipulate the magnetization orientation of magnetic domains
A typical magneto-ionic structure is composed of a ferromagnetic layer in contact with an oxide reservoir layer from which oxygen ions are transported, modifying the target material’s structure and stoichiometry, with corresponding changes in coercive field, exchange bias field, magnetic easy axis, or magnetic anisotropy.[8−10,12,17,19−23] Cyclability remains an issue as ionic transport may result in irreversible structural changes
Rietveld refinement of the FeN X-ray diffraction (XRD) patterns reveals that the hcp phases of both films are distorted, and the films are highly nanocrystalline, with the smallest crystallite sizes in the range of 10−14 nm
Summary
Modern electronic devices store data using electric current to manipulate the magnetization orientation of magnetic domains. With device miniaturization pushing nominal device dimensions toward 10 nm, greater amounts of energy are expended due to resistive heating and device cooling This challenge has spurred research toward discovering novel materials and developing new devices for next-generation technologies with improved energy efficiency, robust thermal stability, and precise control of magnetic properties. Voltagecontrolled magnetism (VCM) tackles this challenge by replacing electric current with an applied voltage, potentially leading to significant energy savings.[1,2] Magneto-ionics,[3−18] a branch of VCM in which ions such as O2−, H+, Li+, F−, or N2−/3− are injected into and withdrawn from a target material under an applied bias, has been shown to be capable of generating large, nonvolatile, and reproducible modulations of bulk magnetic observables. Ionic motion on the order of 103 Hz has been successfully demonstrated with good endurance via a proton-based (H+) mechanism, albeit with some limitations in the operational film thicknesses and hydrogen retention.[11]
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