Influence of nonstoichiometry on the Verwey transition in Fe3(1−δ)O4

Aragón, R.; Shepherd, J.; Koenitzer, J. W.; Buttrey, Douglas J.; Rasmussen, R. J.; Honig, J.M.

doi:10.1063/1.335156

Cited by 57 publications

(48 citation statements)

References 3 publications

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“…Consequently, it is not surprising that these surfaces, where reduction and oxidation ultimately take place, are based on these different phases, and that typical defects are related to excess or missing cations. Similar behaviour can be expected from oxides with similar bulk properties, for example those of Ni, Mn, and Co. (100) surface, which they propose to be stabilized by anti-site defects [572]. The first STM/AFM images of the Fe 3 O 4 (100) surface shown in Figure 29 reveal the large undulations observed in STM to be predominantly of electronic origin.…”

Section: Boron (B)mentioning

confidence: 52%

“…For more information regarding the Verwey transition the reader is directed to an extensive review by Walz [33] and the latest work by the Attfield group [73; 74]. Interestingly, the transition temperature is known to depend on a variety of factors, including stoichiometry [100], purity and strain. In this author's research group, the Verwey transition temperature of new Fe 3 O 4 single crystals is measured to assess the stoichiometry and purity of samples prior to using them for surface science studies.…”

Section: Surface Verwey Transitionmentioning

confidence: 99%

“…The authors propose that the promotional effect of Cu could be linked to providing sites to adsorb CO, thereby preventing poisoning of the surface by adsorbed water (see Figure 97). (100), and found that only pure Fe 3 O 4 (100) exhibited a (√2×√2)R45° reconstruction in RHEED, and that all Ti-containing films exhibit a bulk-terminated (and therefore polar) spinel surface. XPS was performed after a transfer through air and the surface was found to be oxidised, but significant Fe 2+ signal was recovered after heating to 623 K in UHV.…”

Section: Coppermentioning

confidence: 99%

“…At V max (the highest sample bias where electrons are emitted), E kin is maximised and both electrons originate from E F . The spin asymmetry at E F is then determined by: (100) surface, but hydrogen adsorption induces a drastic enhancement. Figure 13 adapted with permission from Ref.…”

Section: Fe 3 O 4 -Half-metallicitymentioning

confidence: 99%

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Iron oxide surfaces

Parkinson

2016

Surface Science Reports

488

463

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The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe 3 O 4 ), maghemite (γ-Fe 2 O 3 ), hematite (α-Fe 2 O 3 ), and wüstite (Fe 1-x O) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe 3 O 4 is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment, and because it is an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed.The best understood iron oxide surface at present is probably Fe 3 O 4 (100); the structure is known with a high degree of precision and the major defects and properties are well characterised. A major factor in this is that a termination at the Fe oct -O plane can be reproducibly prepared by a variety of methods, as long as the surface is annealed in 10 Such straightforward preparation of a monophase termination is generally not the case for other iron oxide surfaces. All available evidence suggests the oft-studied (√2×√2)R45° reconstruction results from a rearrangement of the cation lattice in the outermost unit cell in which two octahedral cations are replaced by one tetrahedral interstitial, a motif conceptually similar to well-known Koch-Cohen defects in Fe (0001) is the most studied hematite surface, but 2 difficulties preparing stoichiometric surfaces under UHV conditions have hampered a definitive determination of the structure. There is evidence for at least three terminations: a bulk-like termination at the oxygen plane, a termination with half of the cation layer, and a termination with ferryl groups. When the surface is reduced the so-called "bi-phase" structure is formed, which eventually transforms to a Fe 3 O 4 (111)-like termination. The structure of the bi-phase surface is controversial; a largely accepted model of coexisting Fe 1-x O and α-Fe 2 O 3 (0001) islands was recently challenged and a new structure based on a thin film of Fe 3 O 4 (111) on α-Fe 2 O 3 (0001) was proposed. The merits of the compet...

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Section: Boron (B)mentioning

confidence: 52%

Section: Surface Verwey Transitionmentioning

confidence: 99%

Section: Coppermentioning

confidence: 99%

Section: Fe 3 O 4 -Half-metallicitymentioning

confidence: 99%

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Iron oxide surfaces

Parkinson

2016

Surface Science Reports

488

463

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“…In the ZFC/FC curves the Verwey transition at 120 K was observed. This transition justified the nanoparticle core constituted by stoichiometric magnetite [44]. Magnetization-temperature curves show a saturation magnetization of about 64 emu/g which therefore much lower than the bulk value of magnetite 92 emu/g, observing additional remanence and coercivity.…”

Section: Resultsmentioning

confidence: 99%

Ultrafine Magnetite Nanopowder: Synthesis, Characterization, and Preliminary Use as Filler of Polymethylmethacrylate Nanocomposites

Russo

Acierno

Palomba

et al. 2012

Journal of Nanotechnology

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Magnetite (Fe 3 O 4 ) nanoparticles prepared by microwave-assisted hydrothermal synthesis have been characterized in terms of morphological and structural features. Electron micrographs collected in both scanning (SEM) and transmission (TEM) modes and evaluations of X-ray powder diffraction (XRD) patterns have indicated the achievement of a monodispersed crystallite structure with particles having an average size around 15-20 nm. Structural investigations by Micro-Raman spectroscopy highlighted the obtainment of magnetite nanocrystals with a partial surface oxidation to maghemite (γ-Fe 3 O 4 ). Preliminary attention has been also paid to the use of these magnetite nanoparticles as filler for a commercial polymethylmethacrylate resin. Hybrid formulations containing up to 3 wt% of nanoparticles were prepared by melt blending and characterized by calorimetric and thermogravimetric tests. For sake of comparison, same formulations containing commercial Fe 3 O 4 nanoparticles are also reported. Calorimetric characterization indicates an increase of both glass transition temperature and thermal stability of the nanocomposite systems when loaded with the synthesized magnetite nanoparticles rather then loaded with the same amount of commercial Fe 3 O 4 . This first observation represents just one aspect of the promising potentiality offered by the novel magnetic nanoparticles when mixed with PMMA.

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Atomic scale spin‐dependent STM on magnetite using antiferromagnetic STM tips

Murphy

Ceballos

Mariotto

et al. 2005

Microscopy Res & Technique

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STM tips made from antiferromagnetic MnNi have been used to investigate the atomic structure of the (001) and (111) surfaces of Fe 3 O 4 . The clean (001) surface displays a (√2 × √2)R45° superlattice, which is attributed to charge-ordering on the surface, where Fe 2+ -Fe 2+ and Fe 3+ -Fe 3+ dimers can be discriminated. The oxygenterminated (111) surface is characterized by an hexagonal superlattice with a periodicity of 42 Å. Oxygen vacancies are observed in atomically resolved images of this superlattice. In the presence of an external magnetic field of 60 mT, a significant change in the atomic corrugation in the topmost oxygen layer around each of these defects is observed. The results on both (001) and (111) surfaces are discussed in terms of possible spin polarized effects.

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Influence of nonstoichiometry on the Verwey transition in Fe3(1−δ)O4

Cited by 57 publications

References 3 publications

Iron oxide surfaces

Iron oxide surfaces

Ultrafine Magnetite Nanopowder: Synthesis, Characterization, and Preliminary Use as Filler of Polymethylmethacrylate Nanocomposites

Atomic scale spin‐dependent STM on magnetite using antiferromagnetic STM tips

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