Anomalous specific heat of CeB6

Fujita, Toyomi; Suzuki, Maroh; Komatsubara, T.; Kunii, S.; Kasuya, T.; Ohtsuka, Toshiya

doi:10.1016/0038-1098(80)90900-x

Cited by 164 publications

(78 citation statements)

References 6 publications

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“…Contrary to the cases of Ce 3 Pd 20 Si 6 and YbRh 2 Si 2 , these fluctuations do not become critical at B c , however, they are critically softened upon doping, indicating a QCP near x c = 0.3, which is hidden inside the enigmatic phase IV. These results outline rich prospects in the research of competing correlated ground states in the structurally simple three-dimensional system CeB 6 .…”

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confidence: 68%

“…CeB 6 was one of the first known AFQ compounds, where the multipolar order was observed both indirectly as an anomaly in specific heat at T Q = 3.2 K [6] and directly by resonant x-ray diffraction [7] or neutron diffraction [8,9] as a weak magnetic Bragg peak centered at the Q AFQ = R( 2 ) propagation vector. The magnetic phase diagram of CeB 6 [8] is similar to that of Ce 3 Pd 20 Si 6 , yet with larger temperature and magnetic-field scales.…”

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confidence: 99%

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Magnetic field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compoundCe1−xLaxB6

et al. 2015

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CeB 6 is a model compound exhibiting antiferroquadrupolar (AFQ) order, its magnetic properties being typically interpreted within localized models. More recently, the observation of strong and sharp magnetic exciton modes forming in its antiferromagnetic (AFM) state at both ferromagnetic and AFQ wave vectors suggested a significant contribution of itinerant electrons to the spin dynamics. Here we investigate the evolution of the AFQ excitation upon the application of an external magnetic field and the substitution of Ce with non-magnetic La, both parameters known to suppress the AFM phase. We find that the exciton energy decreases proportionally to T N upon doping. In field, its intensity is suppressed, while its energy remains constant. Its disappearance above the critical field of the AFM phase is preceded by the formation of two modes, whose energies grow linearly with magnetic field upon entering the AFQ phase. These findings suggest a crossover from itinerant to localized spin dynamics between the two phases, the coupling to heavy-fermion quasiparticles being crucial for a comprehensive description of the magnon spectrum.PACS numbers: 75.30. Mb, 75.30.Ds, 78.70.Nx A current focus of research in heavy fermion (HF) compounds is the study of quantum critical points (QCP) -phase transitions achieved at zero temperature by tuning an external parameter such as magnetic field, doping, or pressure. One possible signature of a QCP is the change of the quasiparticle character from localized to itinerant, when the transition is connected with a breakdown of the Kondo effect and the removal of f-electrons from the Fermi surface (FS). Such an effect was observed, for example, by transport measurements in the prototypical QCP system YbRh 2 (Si 1−x Ge x ) 2 at the critical field of the lowtemperature antiferromagnetic (AFM) phase [1, 2]. Recently, the list of QCP materials was extended with the cubic Kondo lattice compound Ce 3 Pd 20 Si 6 [3][4][5], whose magnetic phase diagram comprises an antiferroquadrupolar (AFQ) phase below T Q = 0.5 K and an AFM phase at even lower temperatures. For the latter phase, a field-induced QCP was observed at the critical field B * = 0.9 T and the concomitant FS reconstruction was related to the destruction of the Kondo effect [3].CeB 6 was one of the first known AFQ compounds, where the multipolar order was observed both indirectly as an anomaly in specific heat at T Q = 3.2 K [6] and directly by resonant x-ray diffraction [7] or neutron diffraction [8, 9] as a weak magnetic Bragg peak centered at the Q AFQ = R(

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Magnetic field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compoundCe1−xLaxB6

et al. 2015

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“…The full entropy of the quartet state is recovered at a much higher temperature ($30 K) than T Q , which indicates the presence of strong fluctuations above T Q . 21,23) A remarkable feature of the phase diagram is that T Q increases as H increases. As discussed generally in §4.3, the AF octupole T xyz induced through the third-order term O xy ðQÞT xyz ðQÞJ z ð0Þ in the free energy stabilizes phase II in a magnetic field.…”

Section: Thermodynamic Anomalymentioning

confidence: 99%

Multipole Orders and Fluctuations in Strongly Correlated Electron Systems

2009

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In this paper we review experimental and theoretical results on higher electronic multipoles in solids with strong correlations. Recent experiments and their theoretical interpretation have confirmed the ordering of octupoles and even higher multipoles in rare-earth and actinide compounds with f electrons. The concept of multipoles is critically examined in point groups where spherical tensors of different ranks mix. Using a phenomenological approach, we demonstrate how linear and nonlinear couplings of different multipoles lead to rich phase diagrams and anomalies in physical observables. As actual representative systems, we first consider Ce x La 1Àx B 6 , for which resonant X-ray scattering probed the octupole order for the first time, and NpO 2 , where quadrupoles induced by the octupole order have been observed. We then consider a class of compounds called skutterudites as the most convenient system for systematic study. Particular emphasis is placed on the ordering of scalar components from fourth-rank tensors (hexadecapoles) and sixth-rank tensors (hexacontatetrapoles). A comparison of a skutterudite PrFe 4 P 12 and URu 2 Si 2 is made, where much fewer carriers remain in the ordered states than in the disordered phase. The even number (two) of f electrons per site in Pr 3þ or U 4þ makes the system free from the Kramers degeneracy, in contrast to standard models for Mott transitions. Hence, it is pointed out that multipole orders, particularly the scalar order, should provide a new route for studying the dichotomy between the itinerant and localized behaviors of electrons.

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“…[1][2][3][4][5][6][7] In particular, the entanglement gives a natural explanation for the longstanding inconsistency between the neutron diffraction and the B 11 -NMR measurements of the phase II.…”

Section: §1 Introductionmentioning

confidence: 99%

Spin-Orbital Wave Excitations in Orbitally Degenerate Exchange Model with Multipolar Interactions

Kusunose

Kuramoto

2001

J. Phys. Soc. Jpn.

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Elementary excitations in the multipole ordered state, which models the phase III in CeB6, are investigated by means of a generalized Holstein-Primakoff formalism. When different kinds of nearest-neighbor exchange interactions between multipoles are comparable to each other, orbitalflip excitations exhibit almost one-dimensional dispersion along the z axis. With high symmetry of the interactions, zero modes appear due to the macroscopic degeneracy of the ground state. The next-nearest-neighbor dipole-dipole interaction, which stabilizes the magnetic order of the phase III in CeB6, lifts the degeneracy and leads to gapfull excitation spectrum. When the octupole-octupole next-nearest-neighbor interaction exists simultaneously, the spectrum shows softening at Γ and Z points. These excitations may be probed by neutron scattering and ultrasonic measurements.KEYWORDS: orbital degeneracy, multipole moment, Holstein-Primakoff transformation, CeB 6 §1. Introduction Among many fascinating compounds with orbital degeneracy, CeB 6 shows an interesting entanglement of dipole, quadrupole as well as octupole moments.1-7) In particular, the entanglement gives a natural explanation for the longstanding inconsistency between the neutron diffraction and the B 11 -NMR measurements of the phase II.8) Namely, the field-induced octupole moment of Γ 2 -type, which arises through the mode mixing with the dipole moment, causes an extra internal field on the B nucleus sites. It explains the unexpected field-angle dependence in the NMR measurement.In discussing the transition from the antiferroquadrupolar (AFQ) phase, called II, to the magnetically ordered phase III, the mode mixing between dipoles and octupoles also plays an important role.9, 10) The present authors have made systematic analysis of multipole modes under the AFQ ordering.11) Then they have discussed effects of multipolar interactions on magnetic phases within the mean-field approximation. In their model Hamiltonian, the pseudo-dipole-type interactions for the next-nearest neighbors (NNN) are indispensable to account for the observed non-collinear magnetic ordering. The usual exchange-type interactions for the nearest neighbors (NN) are also important.What they found are the followings: 11) (i) the competition between the NN dipole-dipole and octupoleoctupole interactions strongly suppresses transition temperatures for simple AF magnetic order, (ii) the ferromagnetic NNN dipole-dipole interaction plays a dominant role in stabilizing the non-collinear ordering in the phase III, and (iii) the AF NNN octupole-octupole interaction is expected to be as strong as the dipole-dipole interaction since the phase III ′ is observed for relatively *

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Anomalous specific heat of CeB6

Cited by 164 publications

References 6 publications

Magnetic field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compoundCe1−xLaxB6

Magnetic field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compoundCe1−xLaxB6

Multipole Orders and Fluctuations in Strongly Correlated Electron Systems

Spin-Orbital Wave Excitations in Orbitally Degenerate Exchange Model with Multipolar Interactions

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