The Jahn-Teller effect and magnetism: transition metal compounds

Кugel, K. I.; Khomskiî, D. I.

doi:10.1070/pu1982v025n04abeh004537

Cited by 1,394 publications

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“…Both Khaliullin et al [64] and Maezono et al [65] realized the importance of the e gorbital degrees of freedom [68,69] in the spin dynamics in FM metallic manganites. The strength of the FM interaction at a given bond strongly depends on the orbital character of e g electrons.…”

Section: Discussion Of Possible Explanationsmentioning

confidence: 99%

Magnons in ferromagnetic metallic manganites

Zhang¹,

Ye²,

Sha³

et al. 2007

J. Phys.: Condens. Matter

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Ferromagnetic (FM) manganites, a group of likely half-metallic oxides, are of special interest not only because they are a testing ground for the classical double-exchange interaction mechanism for the 'colossal' magnetoresistance, but also because they exhibit an extraordinary arena of emergent phenomena. These emergent phenomena are related to the complexity associated with strong interplay between charge, spin, orbital, and lattice. In this review, we focus on the use of inelastic neutron scattering to study the spin dynamics, mainly the magnon excitations in this class of FM metallic materials. In particular, we discuss the unusual magnon softening and damping near the Brillouin zone boundary in relatively narrow-band compounds with strong Jahn-Teller lattice distortion and charge-orbital correlations. The anomalous behaviours of magnons in these compounds indicate the likelihood of cooperative excitations involving spin and lattice as well as orbital degrees of freedom.

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Section: Discussion Of Possible Explanationsmentioning

confidence: 99%

Magnons in ferromagnetic metallic manganites

Zhang¹,

Ye²,

Sha³

et al. 2007

J. Phys.: Condens. Matter

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“…(1), also includes a biquadratic interchain interaction. At J ⊥ = 0 the model (58) is known as the spin-orbital chain [29] and has been recently studied by different groups (see e.g. [30,8,31]).…”

Section: Summary and Discussionmentioning

confidence: 99%

“…(62), (63) lead to the correspondence (29). Therefore, the hidden SU(2) symmetry of the following model of two coupled QI chains …”

Section: Summary and Discussionmentioning

confidence: 99%

Ising model description of the SU(2)1 quantum critical point in a dimerized two-leg spin-1/2 ladder

Wang¹,

Nersesyan²

2000

Nuclear Physics B

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A nonperturbative analytical description of the SU(2) 1 quantum critical point in an explicitly dimerized two-leg spin-1/2 Heisenberg ladder is presented. It is shown that this criticality essentially coincides with that emerging in a weakly dimerized spin-1 chain with a small Haldane gap. The approach is based on the mapping onto an SO(3)-symmetric model of three strongly coupled quantum Ising chains. This mapping is used to establish the correspondence between all physical fields of the spin ladder and those characterizing the SU(2) 1 criticality at the infrared fixed point.

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“…[4] ROO ground state was found because JT coupling with only tetragonal distortion in z-direction was pre-introduced. However, the inclusion of a local JT coupling with cubic symmetry will not affect the above results, as each state from the manifold would gain the same amount of JT energy by an elongation of each VO 6 octahedron along the local tetragonal axis [10].…”

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confidence: 99%

“…First we discuss H SE . The insulating phase of AV 2 O 4 is of Mott-Hubbard type and the SE interaction can be described by the KugelKhomskii model [10]. We borrow the SE Hamiltonian for V 3+ ions, with three-fold degenerate t 2g orbitals and spin S=1, from Ref.…”

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confidence: 99%

Orbital order in vanadium spinels

2005

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Motivated by recent theoretical and experimental controversy, we present a theoretical study to clarify the orbital symmetry of the ground state of vanadium spinel oxides AV2O4 (A=Zn, Mg, Cd). The study is based on an effective Hamiltonian with spin-orbital superexchange interaction and a local spin-orbit coupling term. We construct a classical phase-diagram and prove the complex orbital nature of the ground state. Remarkably, with our new analysis we predict correctly also the coherent tetragonal flattening of oxygen octahedra. Finally, through analytical considerations as well as numerical ab-initio simulations, we propose how to detect the predicted complex orbital ordering through vanadium K edge resonant x-ray scattering.PACS numbers: 75.10. Jm, 75.30.Et Vanadium and titanium spinels, AB 2 O 4 (B=Ti 3+ , or V 3+ ), belong to a class of frustrated antiferromagnets where magnetic B-ions are characterized by orbital degeneracy due to partial occupancy of t 2g -orbitals (n t2g =1 for titanates and n t2g =2 for vanadates). Recently these spinels were thoroughly studied from both experimental [1,2,3] and theoretical [4,5,6] points of view. While the ground state of Ti-based spinels can be explained in terms of orbitally-driven superexchange interactions on the frustrated pyrochlore lattice [6], the situation seems not so fluid for vanadium spinels, as two conflicting theoretical works appeared to explain their structural and magnetic properties [4,5].In AV 2 O 4 , magnetically active V 3+ -ions form a pyrochlore lattice and are characterized by two 3d electrons in t 2g -orbitals, while A is a divalent ion like Cd 2+ , or Zn 2+ , or Mg 2+ . All compounds show qualitatively similar structural and magnetic behavior with a structural transition at a higher temperature T S and an antiferromagnetic (AFM) transition at a slightly lower temperature T N [7]. These findings have been interpreted by Tsunetsugu and Motome [4] as an interplay of ddσ superexchange (SE) interaction and geometrical frustration: they showed that ordering of orbitals can partially remove magnetic frustration and explain the experimentally observed magnetic structure which is composed of AFM chains running in [110] and [110] directions. The ground state orbital ordering suggested in Ref.[4] consists of stacked ab planes with alternating d xz and d yz vanadium hole orbitals (hereafter referred to as ROO).On the other side Tchernyshyov [5] pointed out that the ground state symmetry I4 1 /a of ROO solution seems at odds with x-ray and neutron diffraction data, indicating a I4 1 /amd space symmetry. Thus, he proposed a purely ionic model where spin-orbit (SO) coupling plays the major role and the V hole occupies (predetermining the sign of Jahn-Teller (JT) distortion) a complex linear combination of xz and yz orbitals: (d xz ± id yz )/ √ 2. (We shall refer to this orbital order as COO).Actually, the correct space group of the system is still elusive. The tetragonal I4 1 /amd space group was found in Ref.[1], while the authors of the neutron scatter...

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The Jahn-Teller effect and magnetism: transition metal compounds

Cited by 1,394 publications

References 6 publications

Magnons in ferromagnetic metallic manganites

Magnons in ferromagnetic metallic manganites

Ising model description of the SU(2)1 quantum critical point in a dimerized two-leg spin-1/2 ladder

Orbital order in vanadium spinels

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