Charge and Orbital Ordering Structure of Fe<sub>3</sub>O<sub>4</sub>in the Low-Temperature Phase as Deduced from NMR Study

Mizoguchi, Moriji

doi:10.1143/jpsj.70.2333

Cited by 34 publications

(42 citation statements)

References 15 publications

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“…Previous reports have revealed that the strength of the anisotropic hyperfine field generated by a 3d electron is tens of Tesla [13], which is of the same magnitude as the local field variation in our NMR spectra.…”

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confidence: 75%

“…Then, the anisotropy hyperfine field generates a different field in the Cr nuclei of each particle and gives rise to a large NMR broadening, especially on the high-frequency side of the peaks. This is explained by an anisotropic hyperfine field term depending on (3sin 2 ÿ 1), where is an angle between the c axis and the direction of the Cr's magnetic moment [13]. Since deviates gradually from zero with increase in the magnetic field, the NMR spectrum should only be broadened on the higher frequency side.…”

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confidence: 99%

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Coexistence of Two Different Cr Ions by Self-Doping in Half-MetallicCrO2Nanorods

et al. 2007

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We investigated the physical properties of Cr ions in half-metallic CrO(2) using 53Cr nuclear magnetic resonance (NMR). The 53Cr NMR spectra showed two peaks with a similar intensity instead of the single peak anticipated from a uniform single valence Cr(+4). Both Cr peaks exhibited a strong anisotropy in the hyperfine field and similar values in the enhancement factor and T2 relaxation time. These results suggest the coexistence of two different Cr ions (provisionally, Cr(+4 +/- 1/3)) by a self-doping effect, which is a likely origin of the metallic ferromagnetism in CrO(2).

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confidence: 75%

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confidence: 99%

Coexistence of Two Different Cr Ions by Self-Doping in Half-MetallicCrO2Nanorods

et al. 2007

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“…6 Further diffraction studies by neutron, 7,8 x-ray, 9 and electron 10 scattering established the monoclinic symmetry of the low temperature (LT) phase realized below T V . Indeed, the number of inequivalent A and B atomic positions found by nuclear magnetic resonance (NMR) for the phase below the VT 11,12,13 agrees with the monoclinic structure.…”

Section: Introductionmentioning

confidence: 66%

Origin of the Verwey transition in magnetite: Group theory, electronic structure, and lattice dynamics study

2007

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The Verwey phase transition in magnetite has been analyzed using the group theory methods. It is found that two order parameters with the symmetries X3 and ∆5 induce the structural transformation from the high-temperature cubic to the low-temperature monoclinic phase. The coupling between the order parameters is described by the Landau free energy functional. The electronic and crystal structure for the cubic and monoclinic phases were optimized using the ab initio density functional method. The electronic structure calculations were performed within the generalized gradient approximation including the on-site interactions between 3d electrons at iron ions -the Coulomb element U and Hund's exchange J. Only when these local interactions are taken into account, the phonon dispersion curves, obtained by the direct method for the cubic phase, reproduce the experimental data. It is shown that the interplay of local electron interations and the coupling to the lattice drives the phonon order parameters and is responsible for the opening of the gap at the Fermi energy. Thus, it is found that the metal-insulator transition in magnetite is promoted by local electron interactions, which significantly amplify the electron-phonon interaction and stabilize weak charge order coexisting with orbital order of the occupied t2g states at Fe ions. This provides a scenario to understand the fundamental problem of the origin of the Verwey transition in magnetite.

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“…Recent 57 Fe NMR experiments have confirmed these site multiplicities. 4,5 Although large, high quality, single crystals of Fe 3 O 4 are available, these tend to microtwin when cooled below the Verwey transition, which frustrates attempts to determine the superstructure displacements by conventional single crystal diffraction experiments. The two published structure determinations, from a detwinned single crystal 6 and from a combined x-ray and neutron powder diffraction experiment, 7,8 have both reported the atomic displacements in a subcell equivalent to a quarter of the full monoclinic cell, in which the 16 B sites are averaged to four unique positions.…”

Section: Charge Order In Fe 3 Omentioning

confidence: 99%

Reply to “Comment on ‘Charge order inFe2OBO3: AnLSDA+Ustudy’”

et al. 2006

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The experimental difficulties of observing Fe 2+ /Fe 3+ charge order in Fe 2 OBO 3 and Fe 3 O 4 are different and are considered separately. Charge order in Fe 3 O 4 has a complex arrangement but is long-range coherent, as evidenced by a recent structure determination and two resonant x-ray diffraction studies. Long-range charge order has not been observed crystallographically in Fe 2 OBO 3 , although there is substantial indirect evidence for Fe 2+ /Fe 3+ ordering over shorter distances. Further support is provided by LSDA+ U calculations on a doubled unit cell of Fe 2 OBO 3 , which shows a charge separation similar to that in Fe 3 O 4 , with a large t 2g subshell occupancy difference that is partially screened by Fe-O covalency.

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Charge and Orbital Ordering Structure of Fe₃O₄in the Low-Temperature Phase as Deduced from NMR Study

Cited by 34 publications

References 15 publications

Coexistence of Two Different Cr Ions by Self-Doping in Half-MetallicCrO2Nanorods

Coexistence of Two Different Cr Ions by Self-Doping in Half-MetallicCrO2Nanorods

Origin of the Verwey transition in magnetite: Group theory, electronic structure, and lattice dynamics study

Reply to “Comment on ‘Charge order inFe2OBO3: AnLSDA+Ustudy’”

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Charge and Orbital Ordering Structure of Fe3O4in the Low-Temperature Phase as Deduced from NMR Study

Cited by 34 publications

References 15 publications

Coexistence of Two Different Cr Ions by Self-Doping in Half-MetallicCrO2Nanorods

Coexistence of Two Different Cr Ions by Self-Doping in Half-MetallicCrO2Nanorods

Origin of the Verwey transition in magnetite: Group theory, electronic structure, and lattice dynamics study

Reply to “Comment on ‘Charge order inFe2OBO3: AnLSDA+Ustudy’”

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Charge and Orbital Ordering Structure of Fe₃O₄in the Low-Temperature Phase as Deduced from NMR Study