Inducing ferromagnetism in epitaxial uranium dioxide thin-film actinides

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Left: strain tuning of oxygen stoichiometry in uranium dioxide; Right: a high-resolution scanning transmission electron microscopy image of UO₂ films.

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Motivated by the breakthroughs over the past decades in complex oxides enabled by thin-film growth technology, a team of Los Alamos materials researchers and external colleagues used the Laboratory’s actinide thin-film capability to explore strain engineering on epitaxial actinide thin films. Strain engineering has been widely used to tune functional properties or create exotic phenomena in thin films, but its application to actinide materials has been sparse.

Published in Advanced Science, the work reveals the correlation among strain, point defects and ferromagnetism in strain engineered uranium dioxide. The team investigated the origin of induced ferromagnetism, or permanent magnetization, in an antiferromagnet uranium dioxide. (Antiferromagnetism is an alignment of electrons resulting in a magnetic moment of zero.) The oxide was chosen due its fundamental interest as a strongly correlated material — a type of material with unusual electronic and magnetic properties — with theoretical studies proposing unique functionalities. The results offer new opportunities to understand the influence of coupled order parameters on the emergent properties of many other actinide thin films.

Actinide materials are an important part of modern technology, playing crucial roles in applications ranging from nuclear energy to quantum computing. Despite this range of service, state-of-the-art research efforts are mainly limited to bulk actinide materials. Extensive theoretical efforts exploring thin-film actinide properties have been made in the past decades, but the research described in Advanced Science represents one of the few experimental studies on physical behaviors that emerge through strongly coupled structural, electronic and magnetic degrees of freedom.

The research team used the Lab’s high-resolution scanning transmission electron microscopy to characterize the film microstructure and the quality of the film-substrate interface of the uranium dioxide films. This work also leverages advanced thin-film synthesis and characterization capabilities at the Center for Integrated Nanotechnologies including pulsed laser deposition, high-resolution thin film x-ray diffractometer and physical property measurement system.

Funding and mission

The Los Alamos portion of the work was funded by the Laboratory Directed Research and Development Program and was performed, in part, at the Center for Integrated Nanotechnologies, a DOE Office of Science user facility operated jointly by Sandia National Laboratories and Los Alamos National Laboratory. This work is also partially funded by the Seaborg Institute, the U.S. Department of Energy and the National Science Foundation. The work supports the Laboratory’s Energy Security mission and the Materials for the Future capability pillar.

Reference

“Induced ferromagnetism in epitaxial uranium dioxide thin films,” Advanced Science, 9, 33 (2022); DOI: 10.1002/advs.202203473. Authors: Yogesh Sharma, Binod Paudel, Matthew M. Schneider, Rico Schönemann, Andrew C. Jones, Marcelo Jaime, Dmitry A. Yarotski, Michael T. Pettes, Ping Yang and Aiping Chen (Los Alamos National Laboratory); Amanda Huon and Timothy Charlton (Oak Ridge National Laboratory); Pinku Roy, Zachary Corey and Quanxi Jia (University at Buffalo); and Michael R. Fitzsimmons (University of Tennessee).

Technical contact: Aiping Chen (MPA-CINT)