Large hidden orbital moments in magnetite

Goering, E.

doi:10.1002/pssb.201147119

Cited by 22 publications

(23 citation statements)

References 63 publications

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“…This argument follows the conclusions of Ref. [9] where it was suggested that the particular stoichiometry could have a large effect on the magnetic moments.…”

supporting

confidence: 55%

“…While the A sites are populated by Fe +3 cations, the B sites have equal populations of (nominally) Fe 3+ [2]. There are many experimental determinations of the magnetite spin and orbital moment, even considering only measurements on single crystals [3][4][5][6][7][8][9][10]. But the wide range of values obtained, from reduced magnetic moments of 1.7 μ B to a value similar to the bulk value 4.3 μ B , together with the observation of significant orbital moment in some cases, have been a cause of concern.…”

mentioning

confidence: 99%

“…But the wide range of values obtained, from reduced magnetic moments of 1.7 μ B to a value similar to the bulk value 4.3 μ B , together with the observation of significant orbital moment in some cases, have been a cause of concern. The large spread of results prompted a detailed study by Goering [9] which points to large orbital moments which are compensated or not depending on the detailed structure and stoichiometry of the magnetite near surface region. The surface role is emphasized by differences between polished and cleaved samples [6].…”

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confidence: 99%

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Spin and orbital magnetic moment of reconstructed2×2R45∘magnetite(001)

et al. 2015

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The surface of a magnetite single crystal with (001) orientation has been prepared by sputtering/annealing cycles providing the √ 2 × √ 2R45• reconstruction. The distribution of magnetic domains on the surface has been imaged by x-ray magnetic dichroism in a photoemission microscope. The easy axes are along the surface in-plane 110 directions. The near-surface magnetic moment was determined by applying the sum rules to XMCD spectra obtained with different kinetic energies of the secondary electrons. A reduced total moment of 3.3 μ B and a ratio of about 0.10 between orbital and spin moment was found, which we attribute to the surface reconstruction.

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“…This argument follows the conclusions of Ref. [9] where it was suggested that the particular stoichiometry could have a large effect on the magnetic moments.…”

supporting

confidence: 55%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Spin and orbital magnetic moment of reconstructed2×2R45∘magnetite(001)

et al. 2015

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“…Over recent years experiments have reported large differences in the magnetic moment, and/or no orbital moment at all [109; 112-114]. In 2011 Goering [115] revisited the topic via XMCD and XAS experiments, and concluded that the simple picture of integer Fe 3+ and Fe 2+ cations is not reasonable, and that the situation is more band-like.…”

Section: Surface Magnetismmentioning

confidence: 99%

Iron oxide surfaces

Parkinson

2016

Surface Science Reports

462

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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“…The presence of integer m spin and vanishing orbital moment (m orb ) of magnetite are expected as an indication for a B-site minority electron conduction mechanism, and its accompanied full spin polarization at the E F . However, concerning with that, controversial results have been reported utilizing techniques such superconducting quantum interference device (SQUID) magnetometer, 11,38 XMCD, 12,27,30,39,38 and magnetic Compton scattering (MCS) 33,34 and calculations with local density approximation (LDA), 30 LDA+U, 30 local spin density approximation (LSDA)+U, 2 and moment analysis etc.. 12 The fundamental magnetic properties of Fe 3 O 4 show strong dependence on the sample preparation methodology. By simultaneous oxidation, Babu et al 32 34 and all the way down to −0.001μ B /f.u.…”

mentioning

confidence: 99%

X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100)

Liu

Song

Maltby

et al. 2015

Journal of Applied Physics

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Abstract:The spin and orbital magnetic moments of the Fe 3 O 4 epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism (XMCD). The ultrathin film retains a rather large total magnetic moment, i.e. (2.73±0.15)μ B /f.u., which is ~ 70% of that for the bulk-like Fe 3 O 4 . A significant unquenched orbital moment up to (0.54±0.05) μ B /f.u. was observed, which could come from the symmetry breaking at the Fe 3 O 4 /MgO interface. Such sizable orbital moment will add capacities to the Fe 3 O 4 -based spintronics devices in the magnetization reversal by the electric field.

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Large hidden orbital moments in magnetite

Cited by 22 publications

References 63 publications

Spin and orbital magnetic moment of reconstructed2×2R45∘magnetite(001)

Spin and orbital magnetic moment of reconstructed2×2R45∘magnetite(001)

Iron oxide surfaces

X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100)

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