Beyond the Interface Limit: Structural and Magnetic Depth Profiles of Voltage-Controlled Magneto-Ionic Heterostructures

TL;DR

This study demonstrates voltage-controlled magneto-ionic effects in thick heterostructures, revealing depth-dependent magnetic and structural changes driven by oxygen migration, which extends control beyond the interface in magnetic devices.

Contribution

It provides the first quantitative depth-resolved mapping of oxygen migration effects in thick magnetic heterostructures, showing bulk and interfacial magnetoelectric coupling beyond the interface limit.

Findings

Oxygen migration affects Co magnetization throughout the film.

Magnetization can be semi-reversibly suppressed and recovered.

GdOx transmits oxygen without sourcing or sinking it.

Abstract

Electric-field control of magnetism provides a promising route towards ultralow power information storage and sensor technologies. The effects of magneto-ionic motion have so far been prominently featured in the direct modification of interface chemical and physical characteristics. Here we demonstrate magnetoelectric coupling moderated by voltage-driven oxygen migration beyond the interface limit in relatively thick AlOx/GdOx/Co (15 nm) films. Oxygen migration and its ramifications on the Co magnetization are quantitatively mapped with polarized neutron reflectometry under thermal and electro-thermal conditionings. The depth-resolved profiles uniquely identify interfacial and bulk behaviors and a semi-reversible suppression and recovery of the magnetization. Magnetometry measurements show that the conditioning changes the microstructure so as to disrupt long-range ferromagnetic ordering, resulting in an additional magnetically soft phase. X-ray spectroscopy confirms electric field induced changes in the Co oxidation state but not in the Gd, suggesting that the GdOx transmits oxygen but does not source or sink it. These results together provide crucial insight into controlling magnetic heterostructures via magneto-ionic motion, not only at the interface, but also throughout the bulk of the films.