Coupling between Spin and Orbital Degrees of Freedom in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>KCuF</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Paolasini, L.; Caciuffo, R.; Sollier, Albéric; Ghigna, Paolo; Altarelli, M.

doi:10.1103/physrevlett.88.106403

Cited by 91 publications

(86 citation statements)

References 23 publications

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“…LDA+ U calculations 55,56 have indicated that such purely electronic interactions would already drive the instability towards the C-type OO ͑C-OO͒ phase, with alternating orbitals in the ab planes, and repeated orbitals along the c axis, which induces FM spin exchange in the ab planes, and strong AF exchange between the planes. Experimentally, this OO sets in below the structural transition at T s ϳ 800 K, 51 i.e., at much higher temperature than the characteristic energy scale of the magnetic excitations, 57 suggesting that the JT effect plays an important role in this instability. This observation is consistent with the large difference between T s and the Néel temperature T N ϳ 38 K, 52 the latter being controlled by the magnetic part of the superexchange, and thus the orbital correlations decouple from the spin-spin correlations.…”

Section: B Spin Exchange Constants and Optical Intensitiesmentioning

confidence: 99%

“…4,19 Orbital order occurs in KCuF 3 below the structural transition at T s ϳ 800 K. At T Ͻ T s the structure is tetragonal, with longer Cu-Cu distances within the ab planes ͑d ab = 8.28 Å͒ than along the c axis ͑d c = 7.85 Å͒, 49 which favors strong AF interactions along the c axis. Below the magnetic transition at T N Ӎ 38 K, long-range magnetic order of A type sets in, 50,51 and the ordered moment is 0 = 0.48 B . 52 The superexchange between the Cu 2+ ions in KCuF 3 , Fig.…”

Section: ͑213͒mentioning

confidence: 99%

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Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

et al. 2005

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The temperature dependence and anisotropy of optical spectral weights associated with different multiplet transitions is determined by the spin and orbital correlations. To provide a systematic basis to exploit this close relationship between magnetism and optical spectra, we present and analyze the spin-orbital superexchange models for a series of representative orbital-degenerate transition metal oxides with different multiplet structure. For each case we derive the magnetic exchange constants, which determine the spin wave dispersions, as well as the partial optical sum rules. The magnetic and optical properties of early transition metal oxides with degenerate t 2g orbitals ͑titanates and vanadates with perovskite structure͒ are shown to depend only on two parameters, viz. the superexchange energy J and the ratio of Hund's exchange to the intraorbital Coulomb interaction, and on the actual orbital state. In e g systems important corrections follow from charge transfer excitations, and we show that KCuF 3 can be classified as a charge transfer insulator, while LaMnO 3 is a Mott insulator with moderate charge transfer contributions. In some cases orbital fluctuations are quenched and decoupling of spin and orbital degrees of freedom with static orbital order gives satisfactory results for the optical weights. On the example of cubic vanadates we describe a case where the full quantum spin-orbital physics must be considered. Thus information on optical excitations, their energies, temperature dependence, and anisotropy, combined with the results of magnetic neutron scattering experiments, provides an important consistency test of the spin-orbital models, and indicates whether orbital and/or spin fluctuations are important in a given compound. I. SUPEREXCHANGE AND OPTICAL EXCITATIONS AT ORBITAL DEGENERACYThe physical properties of Mott ͑or charge transfer͒ insulators are dominated by large on-site Coulomb interactions ϰU which suppress charge fluctuations. Quite generally, the Coulomb interactions lead then to strong electron correlations which frequently involve orbitally degenerate states, such as 3d ͑or 4d͒ states in transition metal compounds, and are responsible for quite complex behavior with often puzzling transport and magnetic properties. 1 The theoretical understanding of this class of compounds, with the colossal magnetoresistance ͑CMR͒ manganites as a prominent example, 2,3 has substantially advanced over the last decade, 4 after it became clear that orbital degrees of freedom play a crucial role in these materials and have to be treated on equal footing with the electron spins, which has led to a rapidly developing field, orbital physics. 5 Due to the strong onsite Coulomb repulsion, charge fluctuations in the undoped parent compounds are almost entirely suppressed, and an adequate description of these strongly correlated insulators appears possible in terms of superexchange. 6 At orbital degeneracy the superexchange interactions have a rather rich structure, represented by the so-called spin-orbita...

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Section: B Spin Exchange Constants and Optical Intensitiesmentioning

confidence: 99%

Section: ͑213͒mentioning

confidence: 99%

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

et al. 2005

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“…Moreover, the electronic and structural properties of KCuF 3 have been recently reexamined by means of LDA+U molecular-dynamic simulations, indicating a possible symmetry change and challenging the original assignment of tetragonal symmetry. 44 This symmetry change seems to allow for a better understanding of Raman, 46 electronic paramagnetic resonance, 47,48 and x-ray resonant scattering 49 properties at T ≈ T N . However, the details of this distortion have not been fully resolved yet.…”

Section: Application To Kcufmentioning

confidence: 99%

Computation of correlation-induced atomic displacements and structural transformations in paramagneticKCuF3andLaMnO3

et al. 2010

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We present a computational scheme for ab initio total-energy calculations of materials with strongly interacting electrons using a plane-wave basis set. It combines ab initio band structure and dynamical mean-field theory and is implemented in terms of plane-wave pseudopotentials. The present approach allows us to investigate complex materials with strongly interacting electrons and is able to treat atomic displacements, and hence structural transformations, caused by electronic correlations. Here it is employed to investigate two prototypical Jahn-Teller materials, KCuF 3 and LaMnO 3 , in their paramagnetic phases. The computed equilibrium Jahn-Teller distortion and antiferro-orbital order agree well with experiment, and the structural optimization performed for paramagnetic KCuF 3 yields the correct lattice constant, equilibrium Jahn-Teller distortion and tetragonal compression of the unit cell. Most importantly, the present approach is able to determine correlation-induced structural transformations, equilibrium atomic positions and lattice structure in both strongly and weakly correlated solids in their paramagnetic phases as well as in phases with long-range magnetic order.

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“…Reported resonant enhancements at transition metal K edges of magnetic scattering intensities were typically very small and often broad (see, e.g., Refs. 34,35,36,37,38), compared to the substantial enhancements often observed at rare earth L edges (see for example Refs. 29,30,31,32).…”

mentioning

confidence: 99%

Distinct order of Gd4fand Fe3dmoments coexisting inGdFe
Angst
¹
,
Kreyßig
²
,
Janssen
³

et al. 2005
Phys. Rev. B
9
0
2
0
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Single crystals of flux-grown tetragonal GdFe4Al8 were characterized by thermodynamic, transport, and x-ray resonant magnetic scattering measurements. In addition to antiferromagnetic order at TN ≈ 155 K, two low-temperature transitions at T1 ≈ 21 K and T2 ≈ 27 K were identified. The Fe moments order at TN with an incommensurate propagation vector (τ, τ, 0) with τ varying between 0.06 and 0.14 as a function of temperature, and maintain this order over the entire T < TN range. The Gd 4f moments order below T2 with a ferromagnetic component mainly out of plane. Below T1, the ferromagnetic components are confined to the crystallographic plane. Remarkably, at low temperatures the Fe moments maintain the same modulation as at high temperatures, but the Gd 4f moments apparently do not follow this modulation. The magnetic phase diagrams for fields applied in [110] and [001] direction are presented and possible magnetic structures are discussed.

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Coupling between Spin and Orbital Degrees of Freedom inKCuF3

Cited by 91 publications

References 23 publications

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

Computation of correlation-induced atomic displacements and structural transformations in paramagneticKCuF3andLaMnO3

Distinct order of Gd4fand Fe3dmoments coexisting inGdFe
Angst
¹
,
Kreyßig
²
,
Janssen
³

et al. 2005
Phys. Rev. B
9
0
2
0
View full text Add to dashboard Cite

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Coupling between Spin and Orbital Degrees of Freedom inKCuF3

Cited by 91 publications

References 23 publications

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

Computation of correlation-induced atomic displacements and structural transformations in paramagneticKCuF3andLaMnO3

Distinct order of Gd4fand Fe3dmoments coexisting inGdFeAngst1, Kreyßig2, Janssen3 et al. 2005Phys. Rev. B9020View full textAdd to dashboardCite

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Distinct order of Gd4fand Fe3dmoments coexisting inGdFe
Angst
¹
,
Kreyßig
²
,
Janssen
³

et al. 2005
Phys. Rev. B
9
0
2
0
View full text Add to dashboard Cite