title: Controllable positive exchange bias via redox-driven oxygen migration.
abstract: Ionic transport in metal/oxide heterostructures offers a highly effective means to tailor material properties via modification of the interfacial characteristics. However, direct observation of ionic motion under buried interfaces and demonstration of its correlation with physical properties has been challenging. Using the strong oxygen affinity of gadolinium, we design a model system of GdxFe1-x/NiCoO bilayer films, where the oxygen migration is observed and manifested in a controlled positive exchange bias over a relatively small cooling field range. The exchange bias characteristics are shown to be the result of an interfacial layer of elemental nickel and cobalt, a few nanometres in thickness, whose moments are larger than expected from uncompensated NiCoO moments. This interface layer is attributed to a redox-driven oxygen migration from NiCoO to the gadolinium, during growth or soon after. These results demonstrate an effective path to tailoring the interfacial characteristics and interlayer exchange coupling in metal/oxide heterostructures.
authors.affiliation: Physics Department, University of California, Davis, One Shields Avenue, Davis, California 95616, USA.|NIST Center for Neutron Research, Gaithersburg, Maryland 20899, USA.
authors.forename: Dustin A
authors.identifier: http://orcid.org/0000-0003-3747-3883
authors.initials: DA
authors.lastname: Gilbert
authors.affiliation: Physics Department, University of California, Davis, One Shields Avenue, Davis, California 95616, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Olamit
authors.affiliation: Physics Department, University of California, Davis, One Shields Avenue, Davis, California 95616, USA.|Department of Physics, University of Gothenburg, Gothenburg 412 96, Sweden.
authors.forename: Randy K
authors.initials: RK
authors.lastname: Dumas
authors.affiliation: NIST Center for Neutron Research, Gaithersburg, Maryland 20899, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Kirby
authors.affiliation: NIST Center for Neutron Research, Gaithersburg, Maryland 20899, USA.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Grutter
authors.affiliation: NIST Center for Neutron Research, Gaithersburg, Maryland 20899, USA.
authors.forename: Brian B
authors.initials: BB
authors.lastname: Maranville
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Elke
authors.initials: E
authors.lastname: Arenholz
authors.affiliation: NIST Center for Neutron Research, Gaithersburg, Maryland 20899, USA.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Borchers
authors.affiliation: Physics Department, University of California, Davis, One Shields Avenue, Davis, California 95616, USA.
authors.forename: Kai
authors.identifier: http://orcid.org/0000-0001-9413-6782
authors.initials: K
authors.lastname: Liu