Microscopic analysis of multipole susceptibility of actinide dioxides: A scenario of multipole ordering in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>AmO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

Hotta, Takashi

doi:10.1103/physrevb.80.024408

Cited by 17 publications

(15 citation statements)

References 49 publications

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“…The CEF ground state of Am 4+ ð5f 5 Þ has been considered to be the magnetic C 7 doublet and likewise for the isoelectronic Pu 3+ [10,21]. Recently, however, a possibility of the magnetic C 8 quartet ground state due to the competition between Coulomb interactions and spin-orbit coupling has been pointed out [22]. In either case, the CEF ground state is magnetic.…”

Section: Nmr Spectrummentioning

confidence: 98%

17O NMR study in (Pu0.91Am0.09)O2

Tokunaga

Osaka

Kambe

et al. 2010

Journal of Nuclear Materials

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Section: Nmr Spectrummentioning

confidence: 98%

17O NMR study in (Pu0.91Am0.09)O2

Tokunaga

Osaka

Kambe

et al. 2010

Journal of Nuclear Materials

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“…We also speculate that the electronic states of AmO 2 might be rather sensitive to disorder, because of the delicately balanced Γ 7 and Γ 8 energies of the 5 f 5 configuration. 34) An NMR study with a fresh sample is clearly required to clarify this point. Figure 2 shows the temperature dependence of the Knight shift.…”

Section: )mentioning

confidence: 99%

“…Recently, Hotta has pointed out that the f 5 ground state is easily converted owing to a competition between spinorbit coupling and Coulomb interactions, so that the ground state could be a Γ 8 quartet for the same CEF potential. 34,35) For such a case, multipolar ordering is expected, since the Γ 8 quartet carries quadrupolar and octupolar degrees of freedom.Recently we have performed an 17 O NMR study for the first time on AmO 2 . 36) In this paper, in order to characterize the magnetic ground states of AmO 2 , we compare our results with those on UO 2 5) and NpO 2 .…”

mentioning

confidence: 99%

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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“…Nevertheless crystal-field calculations [7] and EPR measurements [8] suggest that the ground state in the paramagnetic phase is the doubly degenerate Γ7 rather than the Γ8 quartet as in NpO 2 , which does not support multipolar order without the concurrent ordering of magnetic dipoles. Recently, using CEF analysis based on the j-j coupling method, the instability of the Γ7 ground state and possibility of stabilization of the Γ8 ground state, which can induce higher order multipoles without inducing a dipole moment have been discussed [9,10]. Moreover, 17 O NMR measurements [11,12] demonstrate that the electronic ground state of AmO 2 is extremely sensitive to disorder and the results are all indicative of short-range, spin-glass-like character for the magnetic transition in AmO 2 .…”

Section: Introductionmentioning

confidence: 99%