Magnetic susceptibility and the phase transition of NpO2

Erdös, Paul; Solt, G.; ⊙ołnierek, Z.; Blaise, A.; Fournier, J.M.

doi:10.1016/0378-4363(80)90149-7

Cited by 69 publications

(57 citation statements)

References 11 publications

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“…Instead, resonant X-ray scattering (RXS) measurements have been reported which suggest the occurrence of a longitudinal, triple-q, 5 AFQ structure in the ordered state [12]. Moreover, the AFQ order has been proposed to be a secondary order parameter in a transition driven by primary 5 antiferro-octupolar (AFO) order [12], since the AFQ order alone can not successfully explain the breaking of time reversal symmetry suggested by susceptibility [20] and SR [21] measurements. The longitudinal triple-q 5 AFO ordered ground state has also been corroborated by recent microscopic calculations based on the j-j coupling scheme [13,14].…”

Section: Npomentioning

confidence: 99%

NMR studies of actinide dioxides

Tokunaga

Sakai

Fujimoto

et al. 2007

Journal of Alloys and Compounds

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Section: Npomentioning

confidence: 99%

NMR studies of actinide dioxides

Tokunaga

Sakai

Fujimoto

et al. 2007

Journal of Alloys and Compounds

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“…[1][2][3][4][5] Recently, resonant X-ray scattering measurements have revealed the occurrence of long-range antiferroquadrupolar (AFQ) ordering as a secondary order parameter below T N . 6) NpO 2 is known to exhibit a rather mysterious phase transition at T 0 = 26 K. The compound was thought for many years to be an antiferromagnet; [7][8][9][10] however, neither Mössbauer spectroscopy 11,12) nor neutron diffraction [13][14][15] detected any ordered moment below T 0 . It is now recognized that the phase transition originates from an octupole moment of Γ 5 symmetry (or other high-order multipoles with the same symmetry) allowed by the Γ 8 quartet CEF ground state of the Np 5f electrons.…”

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NMR Study on AmO₂: Comparison with UO₂and NpO₂

et al. 2011

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Recently, 17 O NMR has been performed for the first time on AmO 2 . We have observed a drastic broadening of the NMR spectrum, along with a sudden drop of NMR signal intensity, below T 0 = 8.5 K. These data provide the first microscopic evidence for a phase transition at this temperature as a bulk property of this system. In this paper, we compare NMR results for AmO 2 with those from UO 2 and NpO 2 . In the ordered state we have recorded an 17 O NMR spectrum with a triangular line shape, which resembles neither that of UO 2 nor NpO 2 . This spectrum indicates that the internal local field H int is distributed very nearly randomly from zero to a maximum value, that is, H max int ∼ 7kOe. The temperature dependences of the Knight shift and the nuclear relaxation rate are also compared.KEYWORDS: actinide dioxide, NMR, phase transition, self-radiation effect Actinide dioxides (AnO 2 : An = U, Np, Pu and Am, etc.) are all cubic insulators with rather well-localized 5 f electrons. The actinide ions have the same tetravalent state, so that the number of 5 f electrons per actinide ion varies systematically, with two for U 4+ , three for Np 4+ , four for Pu 4+ and five for Am 4+ in the same cubic fluorite structure. In f -electron systems, the f -electron state is represented in terms of multipole degrees of freedom. Available multipoles on each material are dependent on the character of the crystalline electric field (CEF) ground state determined by the number of f -electrons as well as the symmetry of the crystal. In the cubic symmetry of AnO 2 , even the higher order multipoles are not quenched, and are found to affect the physical properties at low temperatures.UO 2 exhibits an antiferromagnetic (AFM) phase transition at T N = 30.8 K. The magnetic order has the transverse triple-q structure with an ordered moment of 1.74µ B /U atom.1-5) Recently, resonant X-ray scattering measurements have revealed the occurrence of long-range antiferroquadrupolar (AFQ) ordering as a secondary order parameter below T N . 6) NpO 2 is known to exhibit a rather mysterious phase transition at T 0 = 26 K. The compound was thought for many years to be an antiferromagnet; 7-10) however, neither Mössbauer spectroscopy 11,12) nor neutron diffraction [13][14][15] detected any ordered moment below T 0 . It is now recognized that the phase transition originates from an octupole moment of Γ 5 symmetry (or other high-order multipoles with the same symmetry) allowed by the Γ 8 quartet CEF ground state of the Np 5f electrons. [16][17][18][19][20][21][22][23][24][25] The longitudinal triple-q Γ 5 antiferrooctupolar (AFO) order scenario was suggested initially by resonant X-ray scattering 17) and then strongly supported from a microscopic viewpoint by 17 O NMR studies. 20,21,[26][27][28] AmO 2 also exhibits a phase transition at T 0 =8.5 K. However, owing to the limited number of experimental data, the mechanism of this phase transition has remained a mystery for more than 30 years. The phase transition was first reported from magnetic susceptibility ...

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“…7,8 Several phenomenological works on the ordered phase have claimed a key role of octupole degree of freedom. 9,10,11,12,13 The CEF states of NpO 2 have been determined by neutron scattering experiment.…”

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Microscopic analysis of multipole susceptibility of actinide dioxides: A scenario of multipole ordering inAmO2

Hotta

2009

Phys. Rev. B

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By evaluating multipole susceptibility of a seven-orbital impurity Anderson model with the use of a numerical renormalization group method, we discuss possible multipole states of actinide dioxides at low temperatures. In particular, here we point out a possible scenario for multipole ordering in americium dioxide. For Am 4+ ion with five 5f electrons, it is considered that the ground state is Γ − 7doublet and the first excited state is Γ − 8 quartet, but we remark that the f 5 ground state is easily converted due to the competition between spin-orbit coupling and Coulomb interactions. Then, we find that the Γ − 8 quartet can be the ground state of AmO2 even for the same crystalline electric field potential. In the case of Γ − 8 quartet ground state, the numerical results suggest that high-order multipoles such as quadrupole and octupole can be relevant to AmO2.

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Magnetic susceptibility and the phase transition of NpO2

Cited by 69 publications

References 11 publications

NMR studies of actinide dioxides

NMR studies of actinide dioxides

NMR Study on AmO₂: Comparison with UO₂and NpO₂

Microscopic analysis of multipole susceptibility of actinide dioxides: A scenario of multipole ordering inAmO2

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Magnetic susceptibility and the phase transition of NpO2

Cited by 69 publications

References 11 publications

NMR studies of actinide dioxides

NMR studies of actinide dioxides

NMR Study on AmO2: Comparison with UO2and NpO2

Microscopic analysis of multipole susceptibility of actinide dioxides: A scenario of multipole ordering inAmO2

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NMR Study on AmO₂: Comparison with UO₂and NpO₂