The role of volume effects in the Verwey transition in magnetite

Brabers, J.H.V.J.; Walz, F.; Kronmüller, H.

doi:10.1088/0953-8984/11/18/304

Cited by 15 publications

(31 citation statements)

References 12 publications

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“…Being aware of these handicaps, Brabers et al [237][238][239] experienced as to what extent an alternative two-state mean-field model, accounting only for Coulomb SR-and LR interactions-which, according to previous analyses [166] should dominate the lowtemperature phase-may be successful for a quantitative description of the Verwey transition and associated parameters of Fe 3 O 4 in the temperature range around T v . Thus, in terms of the Ihle-Lorenz formalism, cf equations ( 8), (9) [166], only the Coulomb interactions U 1 and U 2as determined from a Madelung approximation over nearest and more distant neighbourshave been accounted for, whereas kinetic (T ik ) and phononic ( ) contributions were neglected.…”

Section: Progress In Theoretical Model Designing (Since 1979)mentioning

confidence: 99%

The Verwey transition - a topical review

Walz¹

2002

J. Phys.: Condens. Matter

700

651

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This review encompasses the story of the Verwey transition in magnetite over a period of about 90 years, from its discovery up to the present. Despite this long period of thorough investigation, the intricate multi-particle system Fe3O4 with its various magneto-electronic interactions is not completely understood, as yet - although considerable progress has been achieved, especially during the last two decades. It therefore appeared appropriate to subdivide this retrospect into three eras: (I) from the detection of the effect to the Verwey model (1913-1947), being followed by a period of: (II) checking, questioning and modification of Verwey's original concepts (1947-1979). Owing to prevailing under-estimation of the role of crystal preparation and qualitiy control, this period is also characterized by a series of uncertainties and erroneous statements concerning the reaction order (one or two) and type of the transition (multi-stage or single stage). These latter problems, beyond others, could definitely be solved within era (III) (1979 to the present) - in favour of a first-order, single-stage transition near 125 K - on the basis of experimental and theoretical standards established in the course of a most inspiring conference organized in 1979 by Sir Nevill Mott in Cambridge and solely devoted to the present topic. Regarding the experimental field of further research, the remarkable efficiency of magnetic after-effect (MAE) spectroscopy as a sensitive probe for quality control and investigation of low-temperature (4 KTv) into a Wigner crystal (T

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Section: Progress In Theoretical Model Designing (Since 1979)mentioning

confidence: 99%

The Verwey transition - a topical review

Walz¹

2002

J. Phys.: Condens. Matter

700

651

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“…1,5 For the basic understanding of Verwey transition, it has been formulated that the interionic Coulomb interactions at octahedral Fe sublattice are playing an important role. Brabers, Walz, and Kronmuller, 6,7 have presented a mean-field approach to Verwey transition based on an effective interionic Coulomb potential and explained the various aspects. In their model they have pointed out that the Verwey transition is strongly dependent upon the bandwidth and interionic Coulomb interaction.…”

Section: Introductionmentioning

confidence: 99%

Swift heavy ion irradiation-induced modifications in structural, magnetic and electrical transport properties of epitaxial magnetite thin films

Kumar

Khan

Srivastava

et al. 2006

Journal of Applied Physics

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The effect of swift heavy ion ͑SHI͒ irradiation ͑190 MeV Ag͒ on structural, electrical transport and magnetic properties of epitaxial magnetite ͑Fe 3 O 4 ͒ thin films ͑thickness ϳ70 nm͒ grown on MgO͗100͘ oriented substrate have been investigated. The x-ray diffraction shows that at low fluence values up to 5 ϫ 10 11 ions/ cm 2 , the strain in the films is relaxed, whereas, at higher fluence range 1 ϫ 10 12 -1 ϫ 10 13 ions/ cm 2 , the epitaxial relationship with the substrate is lost along with a phase transformation from magnetite to more oxidized magnetite phase ͑i.e., maghemite͒. The Verwey transition temperature measured by electrical transport is found to increase from 109 to 117 K with the low fluence SHI irradiation, which is related to the irradiation induced strain relaxation and structural modifications. At higher fluences the system did not show Verwey transition and the resistance is also increased. The similar results were obtained by magnetization studies. The observed magnetization at 1 T field is increased at low fluence suggesting the reduction of areas with frustrated exchange interactions associated with the cationic arrangement at the anti phase boundaries. At higher fluences it decreases monotonically, indicating the emergence of other phases. The observed modifications are explained on the basis of structural strain and disorder induced by swift heavy ions, which lead to modification of the interionic Coulomb potential at octahedral sublattices and bandwidth in this system.

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“…The transition is of the first order, but this attribute applies only to a small nonstoichiometry range with respect to both oxygen and aliovalent dopants (6,7). Attempts have been made (8)(9)(10)(11)(12)(13) to present a theoretical model dealing with both the first-and higher-order Verwey transition. These mean-field approximations describe the transition as an entropy-driven ordering accompanied by a volume effect.…”

Section: Introductionmentioning

confidence: 99%