Crystal structure and magnetism of actinide oxides: A review

In actinide systems, the 5f electrons experience a uniquely delicate balance of effects and interactions
having similar energy scales, which are often difficult to properly disentangle. The interplay
of factors such as the dual character of 5f-states, competing interactions, and strong spin-orbit coupling
results in magnetically unusual and intriguing behavior: multi-k antiferromagnetic ordering,
multipolar ordering, mixed valence configurations, and more. Despite the inherent allure of their
exotic properties, the exploratory science of even the more basic, binary systems like the actinide
oxides has been extremely limited due to their toxicity, radioactivity, and reactivity. In this article,
we provide an overview of the available synthesis techniques for selected binary actinide oxides,
including the actinide dioxides, sesquioxides, and a selection of the higher oxides. For these oxides,
we review and evaluate the current state of knowledge on their crystal structures and magnetic
properties. In many aspects, substantial knowledge gaps exist in the current body of research on
actinide oxides related to understanding their magnetic ground states. Bridging these gaps is vital
for improving not only a fundamental understanding of these systems but also of future nuclear
technologies. To this end, we note the experimental techniques and necessary future investigations
which may aid in better elucidating the nature of these fascinating systems.