Orbital Antiferromagnetism in CeB<sub>6</sub>

Ohkawa, Fusayoshi J.

doi:10.1143/jpsj.54.3909

Cited by 76 publications

(73 citation statements)

References 16 publications

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“…The strength of the NN interactions mediated by conduction electrons was discussed 9,10,23) on the basis of the group-theoretical argument, where it was concluded that there are only two independent couplings.…”

Section: 3)mentioning

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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Section: 3)mentioning

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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“…For example quadrupolar [2][3][4] and octupolar ordering [5,6] induced through the charge (or orbital) degree of freedom have been observed in several strongly correlated electron systems.…”

Section: Introductionmentioning

confidence: 99%

Muon spin relaxation and neutron diffraction investigations of quadrupolar and magnetically ordered states of YbRu2Ge2

et al. 2011

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The magnetic and quadrupolar ordered states of polycrystalline YbRu 2 Ge 2 have been investigated using zero-field muon spin relaxation (µSR) and neutron diffraction measurements. Specific heat measurements show three successive phase transitions, with decreasing temperature from a paramagnetic to a quadrupolar state at T 0 ~ 10 K, from the quadrupolar to a magnetic state at T 1 ~ 6.5 K and a possible change in the magnetic ground state at T 2 ~ 5.5 K. Clear evidence for the magnetic transition below 7 K (spectrum at 8 K reveals paramagnetic state) and a likely change in the magnetic structure near 5.8 K is

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“…Uimin and Brenig [51], on the other hand, proposed a different approach emphasizing crystalline fields. For CeB 6 , quadrupolar interactions between sites [52], the RKKY interaction arising from the Coqblin-Schrieffer model [53,54], and a detailed group theoretical study [55] have been presented.…”

Section: Ferromagnetic Correlations In Phase II Of Cebmentioning

confidence: 99%

Theory of Electron Spin Resonance in Ferromagnetically Correlated Heavy Fermion Compounds

Schlottmann

2018

Magnetochemistry

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Abstract:We studied the electron spin resonance (ESR) line width for localized moments within the framework of the Kondo lattice model. Only for a sufficiently small Kondo temperature can an ESR signal be observed for a Kondo impurity. On the other hand, for a Kondo lattice representing a heavy fermion compound, short-range ferromagnetic correlations (FM) between the localized moments are crucial to observe a signal. The spin relaxation rate (line width) and the static magnetic susceptibility are inversely proportional to each other. The FM enhance the susceptibility and hence reduce the line width. For most of the heavy fermion systems displaying an ESR signal, the FM order arises in the ab-plane from the strong lattice anisotropy. CeB 6 is a heavy fermion compound with cubic symmetry having a Γ 8 ground-quartet. Four transitions are expected for individual Ce ions with a Γ 8 ground-multiplet, but only one has been observed. Antiferro-quadrupolar order (AFQ) arises below 4 K due to the orbital content of the Γ 8 -quartet. We addressed the effects of the interplay of AFQ and FM on the ESR line width and the phase diagram. It is usually difficult to distinguish among ESR resonances due to localized moments and conducting heavy electron spins, especially for anisotropic Ce and Yb compounds. However, for CeB 6 , an itinerant picture within the AFQ phase is necessary to explain the electron spin resonances. The longitudinal magnetic susceptibility has a quasi-elastic central peak of line width 1/T 1 and inelastic peaks for the absorption/emission of excitations. The latter are measured via inelastic neutron scattering (INS) and provide insights into the magnetic order. We briefly summarize some of the INS results for CeB 6 in the context of the picture that emerged from the ESR experiments.

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Orbital Antiferromagnetism in CeB₆

Cited by 76 publications

References 16 publications

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

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

Muon spin relaxation and neutron diffraction investigations of quadrupolar and magnetically ordered states of YbRu2Ge2

Theory of Electron Spin Resonance in Ferromagnetically Correlated Heavy Fermion Compounds

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Orbital Antiferromagnetism in CeB6

Cited by 76 publications

References 16 publications

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

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

Muon spin relaxation and neutron diffraction investigations of quadrupolar and magnetically ordered states of YbRu2Ge2

Theory of Electron Spin Resonance in Ferromagnetically Correlated Heavy Fermion Compounds

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Orbital Antiferromagnetism in CeB₆