Thermoelectric properties of magnetite at the Verwey transition

Kuipers, A. J. M.; Brabers, V.A.M.

doi:10.1103/physrevb.14.1401

Cited by 116 publications

(40 citation statements)

References 37 publications

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“…To investigate the presence of impurities and confirm the non-stoichiometric Fe 3 O 4 nanowires' character, the study of the thermoelectric properties at the Verwey transition (T v ) has been envisaged. Kuipers et al analysed thermoelectric power measurements on pure and doped magnetite crystals, and concluded that minor changes in stoichiometry have a deep influence on whether p-or n-type conduction is observed below T v [17]. Figure 2(b) displays the evolution of the absolute thermoelectric power with the temperature.…”

Section: Structural Propertiesmentioning

confidence: 99%

Magnetotransport properties depending on the nanostructure of Fe₃O₄nanowires

Abid

Abid²,

Serrano-Guisan³

et al. 2006

J. Phys.: Condens. Matter

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We have studied the magnetic behaviour of Fe 3 O 4 nanowires (NWs) with two different diameter ranges, above 150 nm and below 60 nm, made by electrodeposition techniques into a polymeric template. The nanowires were characterized using various techniques, in particular Mössbauer and thermoelectrical power measurements. The stoichiometric distribution of Fe cations showed clearly the presence of the magnetite inverse spinel electronic structure. Structural analysis performed using high-resolution transmission electron microscopy revealed two kinds of nanowire morphologies depending on the size. For nanowires above 150 nm in diameter, a contiguous network of well-bound nanoparticles was obtained. Instead, with a diameter of 60 nm, a polycrystalline structure was observed. The largest nanowires presented a magnetoresistance (MR) greater than 10%, whereas the thinner nanowires had almost none.

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Section: Structural Propertiesmentioning

confidence: 99%

Magnetotransport properties depending on the nanostructure of Fe₃O₄nanowires

Abid

Abid²,

Serrano-Guisan³

et al. 2006

J. Phys.: Condens. Matter

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“…However, dc passes through a maximum around 300 K and then decreases with increasing temperature like a metal. Metal models feature various explanations 8,16,17 for the ''anomalous'' variation of dc above T V . Unfortunately, a direct and model-free separation of the charge carrier number and mobility entering dc above T V has not been achieved.…”

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confidence: 99%

“…Unfortunately, a direct and model-free separation of the charge carrier number and mobility entering dc above T V has not been achieved. Analysis of temperaturedependent thermopower data assumed a zero gap 17 and then inferred an activated mobility. Different Hall effect studies 14,[18][19][20] reach differing conclusions about the number and sign of the carriers, e.g., at 300 K, ranging from 1 4 electron/Fe 3 O 4 molecule 14 to one hole/Fe 3 O 4 molecule.…”

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confidence: 99%

Single-particle gap above the Verwey transition inFe3O4

et al. 1997

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The Verwey transition in magnetite, Fe 3 O 4 , has been studied using temperature-dependent high-resolution photoemission spectroscopy. On heating through the transition temperature T V the band gap is not collapsed, but is merely reduced by ϳ50 meV, showing that a metal-insulator transition does not occur. The change in the gap is perfectly consistent with the two orders of magnitude conductivity jump at T V . Thus even above T V short-range charge ordering rather than site equivalency dominates the single-particle excitations and the electrical properties. We also point out important implications for efforts to model the electrical transport above T V . ͓S0163-1829͑97͒03419-X͔ Magnetite, Fe 3 O 4 , is the archetype mixed valent 3d transition metal compound. Fe 3 O 4 crystallizes in an inverted cubic spinel structure in which tetrahedral A sites contain onethird of the Fe ions as Fe 3ϩ , while octahedral B sites contain the remaining Fe ions, with equal numbers of Fe 3ϩ and Fe 2ϩ in B3 and B2 sites, respectively. Below 860 K, magnetite is ferrimagnetic with the A-site magnetic moments aligned antiparallel to the B-site moments. Immediately apparent is the fundamental tension between the mixed valence of the B sites and their crystallographic equivalence in this crystal structure. This tension is manifested in a first order phase transition, the so-called Verwey transition 1 at T V Ϸ120 K, in which the dc conductivity abruptly increases by two orders of magnitude on heating through T V . 2 Although a large number of papers 3,4 have been published since its discovery in 1941, the Verwey transition was the subject of an entire international workshop 3 as recently as 1979 and continues as a paradigm of the classic condensed matter problem-how to describe electron motion if the kinetic energy, electron-electron interactions, and electron-lattice interaction are all comparably important.Verwey and Haayman 1 interpreted the transition as an order-disorder transformation of Fe ions on the B sites. Indeed, studies by electron and neutron diffraction and nuclear magnetic resonance [5][6][7] show that below T V the B2 and B3 sites are structurally distinguishable in a distorted crystal PHYSICAL REVIEW B CONDENSED MATTER THIRD SERIES, VOLUME 55, NUMBER 19 15 MAY 1997-I BRIEF REPORTSBrief Reports are accounts of completed research which, while meeting the usual Physical Review B standards of scientific quality, do not warrant regular articles. A Brief Report may be no longer than four printed pages and must be accompanied by an abstract. The same publication schedule as for regular articles is followed, and page proofs are sent to authors.

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“…26 The single crystals have been annealed and cooled under equilibrium conditions to obtain highly stochiometric single crystals. 27 The vacancy concentration of the used Fe 3−x O 4 single crystal is smaller than x Ͻ 10 −6 , proven by measuring magnetic after spectra.…”

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confidence: 99%