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. Here 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. These studies demonstrate that dilatometry in high fields is an effective method to investigate the magneto-structural coupling in actinide materials.

SHRESTHA K;  ANTONIO D.;  JAIME Marcelo;  HARRISON N.;  MAST Daniel;  SAFARIK D.;  DURAKIEWICZ T.;  GRIVEAU Jean-Christophe;  GOFRYK Krzysztof; 

2017-09-01

NATURE PUBLISHING GROUP

JRC107163

2045-2322,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC107163,   

10.1038/s41598-017-06154-7,