title: Structural and magnetic depth profiles of magneto-ionic heterostructures beyond the interface limit.
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 been prominently featured in the modification of interface characteristics. Here, we demonstrate magnetoelectric coupling moderated by voltage-driven oxygen migration beyond the interface in relatively thick AlOx/GdOx/Co(15 nm) films. Oxygen migration and Co magnetization are quantitatively mapped with polarized neutron reflectometry under electro-thermal conditioning. The depth-resolved profiles uniquely identify interfacial and bulk behaviours and a semi-reversible control of the magnetization. Magnetometry measurements suggest changes in the microstructure which disrupt long-range ferromagnetic ordering, resulting in an additional magnetically soft phase. X-ray spectroscopy confirms 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 magnetism via magneto-ionic motion, both at interfaces and throughout the bulk of the films.
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, 20899, Maryland, USA. dustin.gilbert@nist.gov.
authors.forename: Dustin A
authors.identifier: http://orcid.org/0000-0003-3747-3883
authors.initials: DA
authors.lastname: Gilbert
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, 20899, Maryland, USA. alexander.grutter@nist.gov.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Grutter
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, 94720, California, USA.
authors.forename: Elke
authors.initials: E
authors.lastname: Arenholz
authors.affiliation: Physics Department, University of California, Davis, 95616, California, USA.
authors.forename: Kai
authors.identifier: http://orcid.org/0000-0001-9413-6782
authors.initials: K
authors.lastname: Liu
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, 20899, Maryland, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Kirby
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, 20899, Maryland, USA.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Borchers
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, 20899, Maryland, USA.
authors.forename: Brian B
authors.initials: BB
authors.lastname: Maranville