Magnetoelectric Measurement of Magnetite (Fe3O4) at Low Temperatures and Direct Evidence for Nonexistence ofacMirror Plane

Miyamoto, Yoko; Shindo, Masahiro

doi:10.1143/jpsj.62.1423

Cited by 33 publications

(23 citation statements)

References 10 publications

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“…Indeed detailed neutron-diffraction studies have proposed Cc symmetry in this supercell. This space group is also compatible with the occurrence of an electric moment found by Miyamoto and Shindo 21 for which a noncentrosymmetric space group is required.…”

Section: Introductionsupporting

confidence: 84%

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Low-temperature structure of magnetite studied using resonant x-ray scattering

et al. 2008

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We propose a model for the Fe atomic displacements in the low-temperature phase of magnetite ͑Fe 3 O 4 ͒, based on the analysis of the photon energy dependence of the scattered intensity of selected reflections in a resonant x-ray scattering experiment. The symmetry of the displacement pattern is forced to be consistent with the Cc space group, long time claimed to be the actual symmetry of the low-temperature phase. Fe positions at octahedral sites and the corresponding charges are accounted for by a fitting procedure comparing simulations and experiment. We found a pattern of small distortions in the a-b plane. An independent sensitivity to the charge occupancy permits to refine the model of charge ordering previously proposed. Finally we have computed the electric moment of the combined charge displacements to be 1.5 C / cm 2 .

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Section: Introductionsupporting

confidence: 84%

“…21 For this to occur charge disproportion on the different pairs of iron sites ͑9-11͒, ͑10-12͒, ͑13-15͒, and ͑14-16͒ has to be of opposite sign. Thus we keep this rule for all the parameters, charges and displacements are opposite on all these pairs of sites.…”

Section: B Sensitivitymentioning

confidence: 99%

Low-temperature structure of magnetite studied using resonant x-ray scattering

et al. 2008

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“…The observation of monoclinic symmetry was also concluded from a single crystal x-ray study [8]. However, in the more recent studies some small deviations from the monoclinic cell have been reported [9,10]. As the issue of definitive, experimentally confirmed crystallographic structure of the low-temperature phase remains controversial, many theoretical models for charge ordering have been proposed: purely electronic [11][12][13], electron-phonon coupled [14][15][16], as well as a bond dimerized ground state without charge separation [17].…”

Section: Introductionmentioning

confidence: 94%

Magnetite: a search for the half-metallic state

Fonin¹,

Dedkov²,

Pentcheva³

et al. 2007

J. Phys.: Condens. Matter

101

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We present a detailed study of the spin-dependent electronic structure of thin epitaxial magnetite films of different crystallographic orientations. Using spin-and angle-resolved photoelectron spectroscopy at room temperature, we determine for epitaxial Fe 3 O 4 (111) films a maximum spin polarization value of −(80 ± 5)% near E F . The spin-resolved photoelectron spectra for binding energies between 1.5 eV and E F show good agreement with the spin-split band structure from density functional theory (DFT) calculations which predict an overall energy gap in the spin-up electron bands in high symmetry directions, thus providing evidence for the half-metallic ferromagnetic state of Fe 3 O 4 in the [111] direction. In the case of the Fe 3 O 4 (100) surface, both the spin-resolved photoelectron spectroscopy experiments and the DFT density of states give evidence for a half-metal to metal transition: the measured spin polarization of about −(55 ± 10)% at E F and the theoretical value of −40% are significantly lower than the −100% predicted by local spin density approximation (LSDA) calculations for the bulk magnetite crystal as well as the −(80 ± 5)% obtained for the Fe 3 O 4 (111) films. The experimental findings were corroborated by DFT calculations as due to a surface reconstruction leading to the electronic states in the majority-spin band gap and thus to the reduced spin polarization.

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“…At low temperatures, the structure of magnetite was proposed to be orthorhombic from nuclear magnetic resonance spectroscopy; [99][100][101] monoclinic from x-ray diffraction, [14,102], neutron diffraction, [15], electron diffraction, [16] and x-ray resonant scattering; [103] or even lower symmetry of triclinic. [104] In the present study, we have restricted our calculation to the room-temperature cubic structure because the calculated thermodynamic properties at ground state can be extrapolated to room temperature without discontinuity by the phase transition.…”

Section: F Lepidocrocite (γ-Feooh)mentioning

confidence: 99%

Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations

Guo

Barnard

2011

Phys. Rev. B

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Iron oxides and oxyhydroxides are challenging to model computationally as competing phases may differ in formation energies by only several kJ mol −1 , they undergo magnetization transitions with temperature, their structures may contain partially occupied sites or long-range ordering of vacancies, and some loose structures require proper description of weak interactions such as hydrogen bonding and dispersive forces. If structures and transformations are to be reliably predicted under different chemical conditions, each of these challenges must be overcome simultaneously, while preserving a high level of numerical accuracy and physical sophistication. Here we present comparative studies of structure, magnetization, and elasticity properties of iron oxides and oxyhydroxides using density functional theory calculations with plane-wave and locally-confined-atomic-orbital basis sets, which are implemented in VASP and SIESTA packages, respectively. We have selected hematite (α-Fe 2 O 3 ), maghemite (γ-Fe 2 O 3 ), goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and magnetite (Fe 3 O 4 ) as model systems from a total of 13 known iron oxides and oxyhydroxides; and use same convergence criteria and almost equivalent settings in order to make consistent comparisons. Our results show both basis sets can reproduce the energetic stability and magnetic ordering, and are in agreement with experimental observations. There are advantages to choosing one basis set over the other, depending on the intended focus. In our case, we find the method using PW basis set most appropriate, and combine our results to construct the first phase diagram of iron oxides and oxyhydroxides in the space of competing chemical potentials, generated entirely from first principles.keywords: iron oxides and oxyhydroxides; phase diagram; density functional theory; modeling and simulation.

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Magnetoelectric Measurement of Magnetite (Fe₃O₄) at Low Temperatures and Direct Evidence for Nonexistence ofacMirror Plane

Cited by 33 publications

References 10 publications

Low-temperature structure of magnetite studied using resonant x-ray scattering

Low-temperature structure of magnetite studied using resonant x-ray scattering

Magnetite: a search for the half-metallic state

Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations

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