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Park, J.H.; Tjeng, L. H.; Allen, J. W.; Metcalf, P.; Chen, C.T.

doi:10.1103/physrevb.55.12813

Cited by 111 publications

(110 citation statements)

References 36 publications

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“…Photoemission spectroscopy results show that the activation energy reduces from 150 to 100 meV on heating through T V . The reduction of activation energy results in a jump of conductivity by a factor of 125 at T V , which is consistent with the two orders of magnitude resistivity jump in bulk Fe 3 O 4 [41]. Below T V , the transport mechanism is more intricate.…”

Section: Transport Propertiessupporting

confidence: 76%

Anisotropic magnetoresistance across Verwey transition in charge ordered Fe3O4 epitaxial films

Liu

Zhang

et al. 2017

Phys. Rev. B

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The anisotropic magnetoresistance (AMR) near the Verwey temperature (T V ) is investigated in charge ordered Fe 3 O 4 epitaxial films. When the temperature continuously decreases below T V , the symmetry of AMR in Fe 3 O 4 (100) film evolves from twofold to fourfold at a magnetic field of 50 kOe, where the magnetic field is parallel to the film surface, whereas AMR in Fe 3 O 4 (111) film maintains twofold symmetry. By analyzing AMR below T V , it is found that the Verwey transition contains two steps, including a fast charge ordering process and a continuous formation process of trimeron, which is comfirmed by the temperature-dependent Raman spectra. Just below T V , the twofold AMR in Fe 3 O 4 (100) film originates from uniaxial magnetic anisotropy. The fourfold AMR at a lower temperature can be ascribed to the in-plane trimerons. By comparing the AMR in the films with two orientations, it is found that the trimeron shows a smaller resistivity in a parallel magnetic field. The field-dependent AMR results show that the trimeron-sensitive field has a minimum threshold of about 2 kOe.

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Section: Transport Propertiessupporting

confidence: 76%

Anisotropic magnetoresistance across Verwey transition in charge ordered Fe3O4 epitaxial films

Liu

Zhang

et al. 2017

Phys. Rev. B

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“…The observation that lattice deformation survives locally in the cubic phase [13] indicates the existence of the precursor shortrange order above T V . It is further supported by photoemission spectroscopy, consistent with the reduction of the single particle gap to ∼ 0.1 eV, not closing completely at T > T V [20]. The long-range order, with larger gap, sets in at T V due to crystal-structural transformation, as was clearly demonstrated in recent high-pressure diffraction experiment [31].…”

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confidence: 78%

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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“…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%

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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Single-particle gap above the Verwey transition inFe3O4

Cited by 111 publications

References 36 publications

Anisotropic magnetoresistance across Verwey transition in charge ordered Fe3O4 epitaxial films

Anisotropic magnetoresistance across Verwey transition in charge ordered Fe3O4 epitaxial films

Mechanism of the Verwey Transition in Magnetite

Terahertz conductivity at the Verwey transition in magnetite

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