Density functional theory investigations into the magnetic ordering of U3 O8

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Abstract

Density functional theory (DFT) has been highly successful in supporting experimental materials science; however, a correct electronic ground state is required to realize the full theoretical capacity of DFT. The uranium oxides, α-U3O8 in particular, are simultaneously technologically important materials and theoretically challenging for DFT because the uranium magnetic ground state is not obvious. This is true for both experiment and theory - magnetic susceptibility measurements indicate an antiferromagnetic (AFM) ground state with transitions near 4.2 and 8.0 K, but the ordering itself is not known. Theoretical literature reports are in contradiction, with independent studies finding paramagnetic, ferromagnetic (FM), and AFM states as the lowest energy configuration. However, recent inelastic neutron scattering experiments suggested an uninvestigated magnetic structure with ordering along the [0.5 1 1] plane, motivating a theoretical reinvestigation. Using this insight, we calculated the relative energy of FM and AFM orderings along [0.5 1 1], [0.5 0 0], [0 1 0], and [0 0 1] using noncollinear DFT calculations with spin-orbital coupling. We found that the [0.5 1 1] AFM structure is lower in energy than FM or AFM orderings along the low Miller index directions. We also investigated polarization of the magnetic moment along each lattice vector and found that polarization along the out-of-plane direction is the energetically preferred orientation for the AFM structures. Additionally, we found in all calculations that moments initially pointing along the in-plane lattice vectors significantly relax until they point along the coordinate between the two crystallographically distinct uranium sites with complex noncollinear magnetic configurations. The new [0.5 1 1] AFM magnetic structure provides an additional path forward toward understanding the electronic structure of α-U3O8 and lends theoretical credibility to recent neutron scattering results.

Original languageEnglish
Article number104409
JournalPhysical Review Materials
Volume6
Issue number10
DOIs
StatePublished - Oct 2022

Funding

This research used resources of the Oak Ridge Leadership Computing Facility, which is a Department of Energy (DOE) Office of Science User Facility supported under Contract No. DE-AC05-00OR22725. The authors would like to thank Dr. E. Nykwest for helpful discussions. This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. DOE. This work is supported by the National Nuclear Security Administration.

FundersFunder number
U.S. Department of Energy
Office of ScienceDE-AC05-00OR22725
National Nuclear Security Administration

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