Crystal-field transitions in<i>f</i>-electron oxides

Kern, S.; Loong, C.‐K.; Lander, G. H.

doi:10.1103/physrevb.32.3051

Cited by 99 publications

(63 citation statements)

References 21 publications

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“…(iii) Among the f 2 states, the Γ 5 triplet is the ground state as observed in UO 2 . Since the CEF excitation energy in UO 2 is as large as 150 meV, 15 we consider only the Γ 5 triplet among f 2 intermediate states to study exchange processes of f 3 ions in NpO 2 . The Γ 8 quartet consists of two Kramers doublets, and it is convenient to introduce orbital index τ (= α, β) to label the two Kramers doublets and spin index σ (=↑, ↓) to distinguish the two states in each Kramers doublet.…”

Section: 11mentioning

confidence: 99%

Analysis off−pmodel for octupole ordering inNpO2

Kubo

Hotta

2005

Phys. Rev. B

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In order to examine the origin of octupole ordering in NpO2, we propose a microscopic model constituted of neptunium 5f and oxygen 2p orbitals. To study multipole ordering, we derive effective multipole interactions from the f -p model by using the fourth-order perturbation theory in terms of p-f hopping integrals. Analyzing the effective model numerically, we find a tendency toward Γ5u antiferro-octupole ordering.PACS numbers: 75.30. Et, 71.10.Fd, 75.40.Cx In the research field of condensed matter physics, it is one of currently important issues to unveil the mechanism of multipole ordering phenomena frequently observed in f -electron systems. It has been widely recognized that quadrupole ordering realizes in several felectron compounds, but recently, in addition to dipole and quadrupole ordering, a possibility of ordering of higher order magnetic multipoles, i.e., octupoles, has been discussed intensively.A typical candidate with octupole ordering is the lowtemperature ordered phase of NpO 2 , 1 since time reversal symmetry is broken in this phase, 2,3 but the detected internal field is too weak to be ascribed to dipole ordering.2,3,4 Indeed, several experimental facts 5,6,7,8 can be consistently explained by assuming longitudinal tripleq Γ 5u octupole ordering.9 In addition, recent experiments on the 17 O NMR also support the triple-q ordered state. 10,11In order to understand why such higher-order multipole order is realized in NpO 2 , it has been highly required to proceed to the microscopic research. In general, it is difficult to develop a microscopic theory for complex multipole ordering in f -electron systems beyond the phenomenological level, but it has been recently proposed to construct a microscopic f -electron model on the basis of a j-j coupling scheme.12 Following this proposal, we have studied the f -electron model on an fcc lattice composed of Np ions with hopping integrals via (f f σ) bonding, and actually found the triple-q octupole ordering.13 However, as shown in Fig. 1(a), oxygen anions exist between Np ions in actual crystal structure. Thus, it is important to clarify how the octupole ordering in the f -electron model is affected by oxygen anions.In this paper, we construct a more realistic model including also p orbitals of oxygen anions in addition to f orbitals of Np ions. We derive an effective multipole interaction model by evaluating the exchange of f electrons via p orbitals within the fourth-order perturbation with respect to p-f hopping integrals. By analyzing the effective model, we again find a tendency toward the triple-q octupole ordered phase, indicating that the f -electron model on the fcc lattice have grasped the essential point on the appearance of octupole ordering of NpO 2 .Let us discuss local f -electron states of actinide dioxides based on the j-j coupling scheme, in which we first include the spin-orbit interaction and consider only the states with total angular momentum j=5/2. From a quantitative viewpoint, this simplification may not be appropriate for actinid...

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Section: 11mentioning

confidence: 99%

Analysis off−pmodel for octupole ordering inNpO2

Kubo

Hotta

2005

Phys. Rev. B

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“…Crystalfield calculations were first performed in the 1960s 13 but a direct observation was not obtained until the first spallation neutron sources became available 14,15 in the 1980s. The crystal-field potential was then found to be a factor of 3 smaller than proposed in Ref.…”

Section: Introductionmentioning

confidence: 99%

Resonant x-ray spectroscopy of uranium intermetallics at the M4,5 edges of uranium

et al. 2017

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We present resonant x-ray emission spectroscopic (RXES) data from the uranium intermetallics UPd3, USb, USn3 and URu2Si2 at the U M4,5 edges and compare the data to those from the well-localized 5f 2 semiconductor UO2. The technique is especially sensitive to any oxidation of the surface, and this was found on the USb sample, thus preventing a good comparison with a material known to be 5f 3 . We have found a small energy shift between UO2 and UPd3, both known to have localized 5f 2 configurations, which we ascribe to the effect of conduction electrons in UPd3. The spectra from UPd3 and URu2Si2 are similar, strongly suggesting a predominant 5f 2 configuration for URu2Si2. The valence-band resonant inelastic x-ray scattering (RIXS) provides information on the U P3 transitions (at about 18 eV) between the U 5f and U 6p states, as well as transitions of between 3 and 7 eV from the valence band into the unoccupied 5f states. These transitions are primarily involving mixed ligand states (O 2p or Pd, Ru 4d) and U 5f states. Calculations are able to reproduce both these low-energy transitions reasonably well.

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“…In the past UO 2 has already been subject to light scattering and neutron scattering investigations [7,8]. IR reflectivity measurements [9] showed 0304-8853/88/$03.50 © Elsevier Science Publishers B.V. …”

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“…Neutron scattering could resolve 5f-CEF excitations in UO 2 [8]. On the other hand, from magnetic susceptibility measurements a magnetic moment of 3.2/~B was determined which deviates considerably from the value 2.83/~ B calculated for a I" 5 CEF ground state [10].…”

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confidence: 99%

Light scattering in heavy fermion compounds

Blumenröder

Brenten

Zirngiebl

et al. 1988

Journal of Magnetism and Magnetic Materials

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We present results of Raman spectroscopy and magnetic susceptibility measurements in the actinide compounds UO 2, UPt 3 and UBel3. The differences in the degree of localization of the 5f-electrons in the insulating UO 2 and in the metallic, heavy fermion compounds UPt 3 and UBel3 are discussed. In both types of compounds we find evidence of localized electronic excitations, which yield a good fit of the magnetic susceptibility data. The spin relaxation rates of UPt 3 and UBel3 at q --0 are determined experimentally from the quasielastic light scattering.

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Crystal-field transitions inf-electron oxides

Cited by 99 publications

References 21 publications

Analysis off−pmodel for octupole ordering inNpO2

Analysis off−pmodel for octupole ordering inNpO2

Resonant x-ray spectroscopy of uranium intermetallics at the M4,5 edges of uranium

Light scattering in heavy fermion compounds

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