Resonant “Forbidden” Reflections in Magnetite

Garcı́a, J.; Subı́as, G.; Proietti, M. G.; Renevier, H.; Joly, Yves; Hodeau, Jean-Louis; Blasco, J.; Sánchez, M. C.; Bérar, J. F.

doi:10.1103/physrevlett.85.578

Cited by 114 publications

(78 citation statements)

References 20 publications

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“…4 + to 2.6 + site to site. 5,6 Thus, the main factor determining the variation of the superxchange due to charge ordering in the ionic model, ͑1/S i S j ͒ in Eq. ͑27͒, is suppressed by covalency.…”

Section: B Implications For Charge Ordering In Magnetitementioning

confidence: 99%

“…4,5 Due to the complexity of the low-temperature structure ͑224 atoms/ unit cell͒ and twinning-related multiple monoclinic domains in the low-temperature phase, conclusive evidence for the existence of charge ordering is a difficult claim. So difficult, in fact, that new evidence is being put forth that raises serious doubts that magnetite is charge ordered at all at low temperatures, 6 opening a new dialogue about this venerable system. 7,8 One property that should be very sensitive to the presence of charge ordering is the spin wave spectrum.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the presence of charge order in magnetite by measurement of the spin wave spectrum

et al. 2006

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Inelastic neutron scattering results on magnetite ͑Fe 3 O 4 ͒ show a large splitting in the acoustic spin wave branch, producing a 7 meV gap midway to the Brillouin zone boundary at q = ͑0,0,1/2͒ and ប = 43 meV. The splitting occurs below the Verwey transition temperature, where a metal-insulator transition occurs simultaneously with a structural transformation, supposedly caused by the charge ordering on the iron sublattice. The wavevector ͑0,0,1/2͒ corresponds to the superlattice peak in the low symmetry structure. The dependence of the magnetic superexchange on changes in the crystal structure and ionic configurations that occur below the Verwey transition affect the spin wave dispersion. To better understand the origin of the observed splitting, several Heisenberg models intended to reproduce the pair-wise variation of the magnetic superexchange arising from both small crystalline distortions and charge ordering were studied. None of the models studied predicts the observed splitting, whose origin may arise from charge-density wave formation or magnetoelastic coupling.

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Section: B Implications For Charge Ordering In Magnetitementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of the presence of charge order in magnetite by measurement of the spin wave spectrum

et al. 2006

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“…Our complete resonant x-ray scattering ͑XRS͒ studies in magnetite demonstrate the lack of CO at the octahedral Fe sites. [8][9][10] In particular, it resolves definitely the controversy on the possible CO with ͓001͔ and ͓001/ 2͔ periodicities. 10 If it exists, the charge disproportionation must be very small ͓lower than 0.1 e− and 0.05 e− for the ͑001͒ and ͑001/ 2͒ periodicities, respectively͔.…”

mentioning

confidence: 99%

“…10 If it exists, the charge disproportionation must be very small ͓lower than 0.1 e− and 0.05 e− for the ͑001͒ and ͑001/ 2͒ periodicities, respectively͔. We only pay attention to two important conclusions of the XRS experiments in magnetite regarding the description of its electronic structure: ͑i͒ the interaction time is extremely short, about 10 −15 sec, so the electron is shared among different octahedral Fe atoms in times lower than this one and ͑ii͒ the observed trigonal anisotropy of the octahedral sites in both, magnetite 8,9 and spinel ferrites. 11 Some resonant x-ray diffraction experiments on magnetite have also remarked on charge segregation along the c axis but their analysis is far from convincing, the anomalous scattering factor was treated as a scalar instead of a tensor.…”

mentioning

confidence: 99%

Comment on “Charge order inFe2OBO3: AnLSDA+Ustudy”

Garcı́a

Subı́as

2006

Phys. Rev. B

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In a recently published paper ͓Phys. Rev. B 72, 014407 ͑2005͔͒, Leonov et al. present an LSDA+ U study of the low temperature monoclinic structure of the iron oxoborate ͑Fe 2 OBO 3 ͒. They report on Fe 2+ -Fe 3+ charge ordering without taking into account recent resonant x-ray scattering experiments, which demonstrate the lack of charge ordering in a closely related oxide such as Fe 3 O 4 . They propose that the charge ordering occurs between equivalent crystallographic sites. First, this result, apart from surprising, is at odds with basic concepts in condensed matter. Second, we argue on the reliability of this theoretical approach, showing that a strong discrepancy is obtained for the calculated total and d-projected charges at Fe atoms with formally the same valence state and local environment between two closed related compounds, Fe 3 O 4 and Fe 2 OBO 3 , using the same theoretical method. Finally, we reconsider the reported theoretical calculations on the basis of a rigorous definition of the concepts of charge and orbital ordering and we show that Fe 2 OBO 3 does not show charge ordering. DOI: 10.1103/PhysRevB.74.176401 PACS number͑s͒: 71.20.Ϫb, 71.28.ϩd, 71.30.ϩh Electronic localization in transition metal ͑TM͒ oxides has continuously been a matter of debate from the beginning of modern investigation. The most widely accepted theory to explain the breakdown of the Bloch band theory, giving rise to conduction in TM oxides derived from Mott's ideas. [1][2][3] This model supports two basic ingredients in the description of the electronic properties of TM oxides; ͑i͒ d electrons are considered as localized at the TM atoms and ͑ii͒ due to this strong localization, the intra-atomic Coulomb repulsion ͑U͒ is considered the relevant parameter. However, these ideas enter in conflict with formally mixed valence TM oxides where two different d n , d n+1 valence states occur. The formal valence of the TM atom has a noninteger value in these oxides so its electronic configuration should be defined as d noninteger . This fractional occupation of the d orbital is in clear contradiction with Mott's ideas of strong d-localization and intra-atomic Coulomb repulsion. In order to overcome this incongruity maintaining Mott's theory, there are two possible solutions either a temporal or a spatial separation. Within the first, the electronic configuration of the TM atom is described as fluctuating between two integer d-electronic configurations, in such a way that the "mobile" electron expends nearly all the time in one configuration, the hopping time from this configuration to the other being long. This is called a fluctuating mixed valence compound. The other possibility is that the two integer d-electronic configurations freeze in the lattice. In such a way, the mixed valence compound is described as a mixture of two ions with different formal valence states, i.e., inhomogeneous mixed-valence state. When the two different valence states localize in an ordered way in the lattice, we call it a charge ordered ͑CO͒ phase. 4 ...

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“…The anisotropy is due to, for instance, d-orbital order-ing [Murakami et al, 1998], distortion ordering [García et al, 2000], charge ordering [Grenier et al, 2002b]. Regarding structural analysis, the polarization dependence may be used as in x-ray absorption.…”

Section: Polarization Dependencementioning

confidence: 99%

Diffraction anomalous fine-structure spectroscopy at beamline BM2 at the European Synchrotron Radiation Facility

Renevier

Grenier

Arnaud

et al. 2003

J Synchrotron Radiat

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Diffraction Anomalous Fine Structure (DAFS) spectroscopy uses resonant elastic x-rays scattering as an atomic, shell and site selective probe that gives information on the electronic structure and the local atomic environment as well as on the long range ordered crystallographic structure. A DAFS experiment consists of measuring the Bragg peak intensities as a function of the energy of the incoming x-ray beam. The French CRG (Collaborative Research Group) beamline BM2-D2AM (Diffraction Diffusion Anomale Multi-longueurs d'onde) at the ESRF (European Synchrotron Radiation Facility) has developed a state of the art energy scan diffraction set-up. In this article, we present the requirements for obtaining reliable DAFS data and report recent technical achievements.

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Resonant “Forbidden” Reflections in Magnetite

Cited by 114 publications

References 20 publications

Investigation of the presence of charge order in magnetite by measurement of the spin wave spectrum

Investigation of the presence of charge order in magnetite by measurement of the spin wave spectrum

Comment on “Charge order inFe2OBO3: AnLSDA+Ustudy”

Diffraction anomalous fine-structure spectroscopy at beamline BM2 at the European Synchrotron Radiation Facility

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