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Title: Tricritical point from high-field magnetoelastic and metamagnetic effects in UN

Uranium nitride (UN) is one of the most studied actinide materials as it is a promising fuel for the next generation of nuclear reactors. Despite large experimental and theoretical efforts, some of the fundamental questions such as degree of 5 f–electron localization/delocalization and its relationship to magneto-vibrational properties are not resolved yet. We show that the magnetostriction of UN measured in pulsed magnetic fields up to 65 T and below the Néel temperature is large and exhibits complex behavior with two transitions. While the high field anomaly is a field-induced metamagnetic-like transition and affects both magnetisation and magnetostriction, the low field anomaly does not contribute to the magnetic susceptibility. Our data suggest a change in the nature of the metamagnetic transition from first to second order-like at a tricritical point at T tri ~24 K and H tri ~52 T. The induced magnetic moment at 60 T might suggest that only one subset of magnetic moments has aligned along the field direction. Using the results obtained here we have constructed a magnetic phase diagram of UN. Our studies demonstrate that dilatometry in high fields is an effective method to investigate the magneto-structural coupling in actinide materials.
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  1. Idaho National Lab. (INL), Idaho Falls, ID (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Idaho National Lab. (INL), Idaho Falls, ID (United States); Univ. of Nevada, Las Vegas, NV (United States). Dept. of Chemistry and Biochemistry, High Pressure Science and Engineering Center
  4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Maria Curie-Sklodowska Univ., Lublin (Poland). Inst. of Physics
  5. European Commission, Karlsruhe (Germany). Joint Research Centre
Publication Date:
Report Number(s):
LA-UR-17-30081; LA-UR-16-28832
Journal ID: ISSN 2045-2322; PII: 6154
Grant/Contract Number:
AC07-05ID14517; DMR-1157490; AC52-06NA25396
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 7; Journal Issue: 1; Journal ID: ISSN 2045-2322
Nature Publishing Group
Research Org:
Idaho National Lab. (INL), Idaho Falls, ID (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
36 MATERIALS SCIENCE; electronic properties and materials; magnetic properties and materials; High Magnetic Field Science
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1407862; OSTI ID: 1412856