Magnetic structures of actinide materials by pulsed neutron diffraction (invited)

Lawson, A. C.; Goldstone, J. A.; Huber, J.G.; Giorgi, A.L.; Conant, J.W.; Severing, A.; Cort, B.; Robinson, R. A.

doi:10.1063/1.348140

Cited by 30 publications

(6 citation statements)

References 5 publications

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“…While earlier works, cited in ref. [1], assume ferromagnetic ground state and Curie temperature coinciding with that of β-UH 3 , a later neutron diffraction work concluded that it is non-magnetic [2]. That would seriously contradict to the concept of U magnetism depending mainly on the 5f-5f overlap.…”

Section: Introductionmentioning

confidence: 87%

UH3-based ferromagnets: New look at an old material

Havela

Paukov

Tkach

et al. 2016

Journal of Magnetism and Magnetic Materials

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UH 3 is the first discovered material with ferromagnetism based purely on the 5f electronic states, known for more than half century. Although the U metal is Pauli paramagnet, the reduced 5f-5f overlap in compounds allows for moment formation and ordering, typically if the U-U spacing exceeds the Hill limit, i.e. about 340 pm. The stable form of UH 3 , known as β-UH 3 , has rather high T C ≈ 170 K. Such high value is rather unusual, considering d U-U = 331 pm. Properties of metastable α-UH 3 with d U-U = 360 pm could be never well established. Using the fact that α-UH 3 is in fact bcc U with interstitials filled by H, we attempted to synthesize α-UH 3 starting from the γ-U alloys, with the bcc structure retained to room temperature by doping combined with ultrafast cooling. While up to 15% Zr a contamination by β-UH 3 was obtained, 20% Zr yielded single phase α-UH 3 . The T C value remains high and very similar to β-UH 3 . One can see an increase up to 187 K for 15% Zr, followed by a weak decrease. Magnetic moments remain close to 1 μ B /U atom. An insight is provided by ab-initio calculations, revealing a a charge transfer towards H-1s states, depopulating the U-6d and 7s states, leaving almost pure 5f character around the Fermi level. The 5f magnetism exhibits a high coercivity (μ 0 H c up to 5.5 T) and large spontaneous volume magnetostriction of 3.2*10 -3 . Even higher increase of T C , reaching up to 203 K, can be achieved in analogous Mo stabilized hydrides, which yield an amorphous structure. The compounds represent, together with known hydrides of U 6 Fe and U 6 Co, a new group of robust 5f ferromagnets with small d U-U but high T C . Although common hydrides are fine powders, some of the new hydrides described as (UH 3 ) (1-x) T x (T = Zr or Mo) remain monolithic, which allows to study transport and thermodynamic properties.

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Section: Introductionmentioning

confidence: 87%

UH3-based ferromagnets: New look at an old material

Havela

Paukov

Tkach

et al. 2016

Journal of Magnetism and Magnetic Materials

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“…While earlier works, reviewed in Ref. 2, deduced magnetic ordering with T C coinciding with that of β-UH 3 , in a later neutron diffraction work it was identified as non-magnetic 15. That would seriously contradict to the concept of the U magnetism depending on the 5 f -5 f overlap.…”

Section: Introductionmentioning

confidence: 92%

Electronic properties ofα−UH3stabilized by Zr

et al. 2015

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Pure hydride of the α-UH type without any β-UH admixture was prepared by high-pressure hydrogenation of U stabilized by Zr. Such material, characterized by a general formula (UH) Zr , is stable in air at ambient and elevated temperatures. H release is observed between 400-450 °C similar to β-UH. Its stability allowed to measure magnetic properties, specific heat, and electrical resistivity in a wide temperature range. Despite rather different crystal structure and inter-U spacing, the electronic properties are almost identical to β-UH. Its ferromagnetic ground state with Curie temperature ≈ 180 K (weakly and non-monotonously dependent on Zr concentration) and U moments of 1.0 μ indicate why mixtures of α- and β-UH exhibited only one transition. Magnetic ordering leads to a large spontaneous magnetostriction = 3.210, which can be explained by the increase of the spin moment between the paramagnetic (Disordered Local Moment) and the ferromagnetic state. The role of orbital moments in magnetism is indicated by fully relativistic electronic structure calculations.

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“…The originally proposed ferromagnetism 12 was later taken as due to the impurity of β-UH 3 . 14 This would require that both αand β-UH 3 should have the same T C value (Curie temperature), which looked unlikely from the point of view of structure differences. Only recently the stabilization of α-UH 3 by Zr alloying confirmed that both phases are very similar, with almost identical magnetic properties.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Even more problematic was synthesis of α-UH 3 , existing as a transient species, converting fast into β-UH 3 . The originally proposed ferromagnetism was later taken as due to the impurity of β-UH 3 . This would require that both α- and β-UH 3 should have the same T C value (Curie temperature), which looked unlikely from the point of view of structure differences.…”

Section: Introductionmentioning

confidence: 99%

Crystal Structure and Magnetic Properties of Uranium Hydride UH₂ Stabilized as a Thin Film

et al. 2018

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A new type of uranium binary hydride, UH2, with the CaF2 crystal structure, was synthesized in a thin-film form using reactive sputter deposition at low temperatures. The material has a grain size of 50–100 nm. The lattice parameter a = (535.98 ± 0.14 pm) is close to that in known Np (534.3 pm) and Pu (535.9 pm) iso-types. UH2 is a metallic ferromagnet with the Curie temperature T C ≈ 120 K. A very wide hysteresis loop indicates strong magnetocrystalline anisotropy. X-ray photoelectron spectroscopy reveals similarities with electronic structure of UH3, which is also ferromagnet with higher T C = 165 K.

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Magnetic structures of actinide materials by pulsed neutron diffraction (invited)

Cited by 30 publications

References 5 publications

UH3-based ferromagnets: New look at an old material

UH3-based ferromagnets: New look at an old material

Electronic properties ofα−UH3stabilized by Zr

Crystal Structure and Magnetic Properties of Uranium Hydride UH₂ Stabilized as a Thin Film

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Magnetic structures of actinide materials by pulsed neutron diffraction (invited)

Cited by 30 publications

References 5 publications

UH3-based ferromagnets: New look at an old material

UH3-based ferromagnets: New look at an old material

Electronic properties ofα−UH3stabilized by Zr

Crystal Structure and Magnetic Properties of Uranium Hydride UH2 Stabilized as a Thin Film

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Product

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Crystal Structure and Magnetic Properties of Uranium Hydride UH₂ Stabilized as a Thin Film