Abstract
The magnetic structure of neptunium dioxide (NpO2) remains a mystery despite decades of research. We revisited the search for magnetic ordering in NpO2 by performing a powder neutron diffraction experiment at low temperatures and relatively large values of Q. Diffraction data were collected for 300 mK, 15 K, and 35 K to understand the phase transition near 25 K. However, no significant changes in the neutron diffraction pattern were identified. Using the octupolar magnetic form factor j6, the maximum theoretical expected value of the magnetic moment (3.27 μB), the calculated magnetic Bragg peak intensities would not be observable in neutron powder diffraction data. This value is much larger than the previously estimated magnetic moment of ∼0.1 μB. Supported by experimental results, these calculations suggest that unpolarized neutron powder diffraction is unsuitable for measuring octupolar ordering in NpO2.
| Original language | English |
|---|---|
| Article number | 123875 |
| Journal | Journal of Solid State Chemistry |
| Volume | 321 |
| DOIs | |
| State | Published - May 2023 |
Funding
This manuscript has been authored by UT-Battelle LLC under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). The authors thank Kaara Patton for helping prepare the NpO 2 specimen. The work performed was supported by the 238 Pu Supply Program at Oak Ridge National Laboratory . Funding for this program was provided by the Science Mission Directorate of the National Aeronautics and Space Administration and administered by the US Department of Energy, Office of Nuclear Energy, under contract DEAC05-00OR22725. This work used resources at the Radiochemical Engineering Development Center and the High Flux Isotope Reactor, both operated by Oak Ridge National Laboratory. Work at Savannah River National Laboratory was supported by the Laboratory Directed Research and Development program.The authors thank Kaara Patton for helping prepare the NpO2 specimen. The work performed was supported by the 238Pu Supply Program at Oak Ridge National Laboratory. Funding for this program was provided by the Science Mission Directorate of the National Aeronautics and Space Administration and administered by the US Department of Energy, Office of Nuclear Energy , under contract DEAC05-00OR22725 . This work used resources at the Radiochemical Engineering Development Center and the High Flux Isotope Reactor, both operated by Oak Ridge National Laboratory . Work at Savannah River National Laboratory was supported by the Laboratory Directed Research and Development program.
Keywords
- Actinide
- High flux isotope reactor
- Magnetism
- Neptunium
- Neutron scattering