High-energy photoemission on Fe
                    <sub>3</sub>
                    O
                    <sub>4</sub>
                    : Small polaron physics and the Verwey transition

Schrupp, D.; Sing, M.; Tsunekawa, M.; Fujiwara, H.; Kasai, S.; Sekiyama, A.; Suga, S.; Matsuki, Takayuki; Brabers, V.A.M.; Claessen, R.

doi:10.1209/epl/i2005-10045-y

Cited by 89 publications

(120 citation statements)

References 33 publications

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“…The estimate of the effective mass m ef f Ӎ 10 2 m has been obtained from the infrared conductivity 14 and from the small-polaron analysis of photoemission of the same sample. 11 With this estimate for m ef f the observed small spectral weight of the Drude process corresponds to ⌬ m Ӎ 40 meV, which correlates with a weakly activated dc conductivity just above T V ͑right inset in Fig. 2͒.…”

Section: ͑3͒mentioning

confidence: 73%

“…This new value of the energy gap agrees with the activation energy of dc conductivity, [18][19][20] thermoelectric power, 12 and with the gap values obtained in photoemission experiments. [9][10][11] The presented description implies the interpretation of the Verwey transition as an insulator-semiconductor transition with a change in activation energy induced by a crystal structure or by electronic configuration.…”

Section: ͑3͒mentioning

confidence: 95%

“…In spite of enormous progress in resolving the low-temperature monoclinic structure of magnetite, [6][7][8] full details could not be completely resolved so far. The monoclinic phase is insulating and is characterized by a gap of the order of 100 meV in the excitation spectrum, which is seen in photoemission data, [9][10][11] in thermoelectric properties, 12 and by optical spectroscopy. 13,14 The charge transport in magnetite is usually explained within a polaronic picture.…”

Section: Introductionmentioning

confidence: 97%

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Terahertz conductivity at the Verwey transition in magnetite

et al. 2005

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The complex conductivity at the (Verwey) metal-insulator transition in Fe3O4 has been investigated at THz and infrared frequencies. In the insulating state, both the dynamic conductivity and the dielectric constant reveal a power-law frequency dependence, the characteristic feature of hopping conduction of localized charge carriers. The hopping process is limited to low frequencies only, and a cutoff frequency ν1 ≃ 8 meV must be introduced for a self-consistent description. On heating through the Verwey transition the low-frequency dielectric constant abruptly decreases and becomes negative. Together with the conductivity spectra this indicates a formation of a narrow Drude-peak with a characteristic scattering rate of about 5 meV containing only a small fraction of the available charge carriers. The spectra can be explained assuming the transformation of the spectral weight from the hopping process to the free-carrier conductivity. These results support an interpretation of Verwey transition in magnetite as an insulator-semiconductor transition with structure-induced changes in activation energy.

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Section: ͑3͒mentioning

confidence: 73%

Section: ͑3͒mentioning

confidence: 95%

Section: Introductionmentioning

confidence: 97%

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Terahertz conductivity at the Verwey transition in magnetite

et al. 2005

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“…31 Below 120 K magnetite undergoes the so-called Verwey transition, 32 where the crystal structure changes from cubic to monoclinic, which is accompanied by an orbital and charge ordering and a drop in conductivity by over two orders-of-magnitude. [33][34][35] The tetrahedral and octahedral sites are antiferromagnetically coupled; resulting in a magnetic moment varying between 3.65 -4.43 μ B , depending on the theoretical model. 11,12,14,15,36 Hence, magnetite is a ferrimagnet, with a large critical temperature of T c = 858 K.…”

Section: Introductionmentioning

confidence: 99%

Controlling the electronic structure of Co1−xFe2+xO
Moyer
¹
,
Vaz
²
,
Negusse
³

et al. 2011
Phys. Rev. B
89
17
74
0
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“…This picture was studied in the Hubbard-like model with interatomic d − d Coulomb interactions [5], but was not confirmed by nuclear magnetic resonance and Mössbauer measurements [6]. While recent resonant soft X-ray scattering suggests charge-orbital ordering within the oxygen 2p states [7] and a cooperative Jahn-Teller effect [8], the microscopic mechanism of the VT remains controversial.…”

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confidence: 99%

Mechanism of the Verwey Transition in Magnetite

2006

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By combining ab initio results for the electronic structure and phonon spectrum with the group theory, we establish the origin of the Verwey transition in Fe3O4. Two primary order parameters with X3 and ∆5 symmetries are identified. They induce the phase transformation from the hightemperature cubic to the low-temperature monoclinic structure. The on-site Coulomb interaction U between 3d electrons at Fe ions plays a crucial role in this transition -it amplifies the coupling of phonons to conduction electrons and thus opens a gap at the Fermi energy. Published in Phys. Rev. Lett. 97, 156402 (2006). PACS numbers: 71.30.+h, 64.70.Kb, 75.50.Gg The discovery of the remarkable discontinuous drop of the electrical conductivity by two orders of magnitude in magnetite (Fe 3 O 4 ) below the Verwey transition (VT) at T V = 122 K [1] triggered intensive studies of its microscopic origin which have been continued for more than six decades. Verwey suggested explaining it by a metalinsulator transition due to the reduction of electron mobility caused by ordering of Fe 3+ and Fe 2+ ions below T V . In spite of great experimental effort, however, the existence of ionic-like charge ordering at T < T V could not be confirmed, and the origin of the VT in magnetite remains still puzzling [2].Magnetite is a ferrimagnetic spinel with anomalously high critical temperature T c ≃ 860 K. Hence, it is viewed as an ideal candidate for room temperature spintronic applications. It crystalizes in the inverse spinel cubic structure, Fd3m, with two types of Fe sites: the tetrahedral A sites and the octahedral B ones, see Ref. There are also other arguments against simple ionic mechanism of the VT. Firstly, the replacement of oxygen O 16 by O 18 isotope increases T V by a few degrees [9], indicating that the transition cannot be purely electronic.Secondly, signals in diffuse neutron scattering observed above T V at k ∆ = (0, 0, 1 2 ), halfway between Γ and X points with k X = (0, 0, 1), and equivalent points of the reciprocal lattice [10] (in units of 2π a , where a is the cubic lattice constant), change into Bragg peaks below T V . The intensity of critical scattering was succesfully calculated on the basis of the transverse acoustic (TA) phonon mode with the ∆ 5 symmetry. Further neutron studies discovered diffuse scattering with large intensities close to Γ and X points, and the dominant component of X 3 symmetry [11]. Other observations from Raman [12], X-ray [13] and nuclear inelastic scattering measurements [14] suggest that phonons play an essential role in the VT. But phonons alone cannot explain the metal-insulator nature of the transition either. Actually, if they alone were responsible, a phonon soft mode would have been found for the cubic phase, while the present ab initio calculations do not imply such a soft mode behavior.The purpose of this Letter is to resolve the above controversies and to demonstrate a cooperative scenario of the VT. Following the pioneering work of Ihle and Lorenz [15], who considered weak intersite Coulom...

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High-energy photoemission on Fe ₃ O ₄ : Small polaron physics and the Verwey transition

Cited by 89 publications

References 33 publications

Terahertz conductivity at the Verwey transition in magnetite

Terahertz conductivity at the Verwey transition in magnetite

Controlling the electronic structure of Co1−xFe2+xO
Moyer
¹
,
Vaz
²
,
Negusse
³

et al. 2011
Phys. Rev. B
89
17
74
0
View full text Add to dashboard Cite

Mechanism of the Verwey Transition in Magnetite

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High-energy photoemission on Fe 3 O 4 : Small polaron physics and the Verwey transition

Cited by 89 publications

References 33 publications

Terahertz conductivity at the Verwey transition in magnetite

Terahertz conductivity at the Verwey transition in magnetite

Controlling the electronic structure of Co1−xFe2+xOMoyer1, Vaz2, Negusse3 et al. 2011Phys. Rev. B8917740View full textAdd to dashboardCite

Mechanism of the Verwey Transition in Magnetite

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High-energy photoemission on Fe ₃ O ₄ : Small polaron physics and the Verwey transition

Controlling the electronic structure of Co1−xFe2+xO
Moyer
¹
,
Vaz
²
,
Negusse
³

et al. 2011
Phys. Rev. B
89
17
74
0
View full text Add to dashboard Cite