Critical role of electrical resistivity in magnetoionics

The critical role of electrical resistivity in governing ion motion in magneto-ionic thin-film systems is demonstrated. A series of highly nanocrystalline cobalt-nitride (Co-N) thin films (85 nm thick) with similar composition but a broad range of electrical properties exhibit markedly different magneto-ionic behavior. Semiconducting, near stoichiometric films show the best performance, better than their metallic- and insulating- counterparts. Resistivity reflects the interplay between atomic bonding, carrier localization and structural defects, which in turn determines the strength and distribution of applied electric fields inside the actuated films. This fact, generally overlooked, reveals that resistivity is a good indicator of the potential of a system to exhibit optimal magneto-ionic effects, while also opening interesting challenges.