Internal magnetic fields in hcp-iron

Taylor, R. D.; Cort, G.E.; Willis, J.O.

doi:10.1063/1.330289

Cited by 45 publications

(35 citation statements)

References 14 publications

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“…Mössbauer spectroscopy shows no evidence of magnetism in hcp Fe (Taylor et al, 1982(Taylor et al, , 1991. X-ray absorption spectroscopy also has been interpreted to show lack of magnetism (Rueff et al, 1999), but due to the absence of an absolute calibration, and sensitivity of the spectrum to changes in the density of states, the experiments show only that magnetic moments are lower in ǫ-Fe than α-Fe, a result consistent with theory.…”

Section: Hcpsupporting

confidence: 73%

Non-collinear magnetism in iron at high pressures

Cohen

2004

Physics of The Earth and Planetary Interiors

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Using a first principles based, magnetic tight-binding total energy model, the magnetization energy and moments are computed for various ordered spin configurations in the high pressure polymorphs of iron (fcc, or γ-Fe, and hcp, or ǫ-Fe), as well ferromagnetic bcc iron (α-Fe). For hcp, a non-collinear, antiferromagnetic, spin configuration that minimizes unfavorable ferromagnetic nearest neighbor ordering is the lowest energy state and is more stable than non-magnetic ǫ iron up to about 75 GPa. Accounting for non-collinear magnetism yields better agreement with the experimental equation of state, in contrast to the non-magnetic equation of state, which is in poor agreement with experiment below 50 GPa.

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Section: Hcpsupporting

confidence: 73%

Non-collinear magnetism in iron at high pressures

Cohen

2004

Physics of The Earth and Planetary Interiors

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“…The magnetic structure of the hcp phase has been the subject of a scientific debate for three decades (6), leading to contradictory results from experiments and theory. Although experiments are interpreted to show the absence of magnetism in hcp iron (6)(7)(8)(9)(10), computations based on density functional theory find an antiferromagnetic (afm) ground state stable to Ϸ50 GPa (11), similar to magnetism in the double hcp phase (5). The possible presence of magnetism in hcp iron as further substantiated in this article has important implications.…”

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confidence: 72%

Magnetism in dense hexagonal iron

Steinle‐Neumann

Stixrude

Cohen

2003

Proc. Natl. Acad. Sci. U.S.A.

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The magnetic state of hexagonal close-packed iron has been the subject of debate for more than three decades. Although Mö ssbauer measurements find no evidence of the hyperfine splitting that can signal the presence of magnetic moments, density functional theory predicts an antiferromagnetic (afm) ground state. This discrepancy between theory and experiment is now particularly important because of recent experimental findings of anomalous splitting in the Raman spectra and the presence of superconductivity in hexagonal close-packed iron, which may be caused by magnetic correlations. Here, we report results from first principles calculations on the previously predicted theoretical collinear afm ground state that strongly support the presence of afm correlations in hexagonal close-packed iron. We show that anomalous splitting of the Raman mode can be explained by spinphonon interactions. Moreover, we find that the calculated hyperfine field is very weak and would lead to hyperfine splitting below the resolution of Mö ssbauer experiments. P hysical properties of iron are of great importance to many fields in the sciences, as iron is one of the most abundant and stable elements in the universe and the very basis for the steel industry. Hexagonal close-packed (hcp) iron, the form stable at high pressure, plays a central role in geophysics, as the Earth's inner core is thought to be primarily composed of this phase (1, 2), and in our understanding of impact and explosive phenomena in iron and steel (3). The magnetic state of iron has a major influence on the physics of iron and iron alloys, including the relative stability of the iron polymorphs (4, 5). The magnetic structure of the hcp phase has been the subject of a scientific debate for three decades (6), leading to contradictory results from experiments and theory. Although experiments are interpreted to show the absence of magnetism in hcp iron (6-10), computations based on density functional theory find an antiferromagnetic (afm) ground state stable to Ϸ50 GPa (11), similar to magnetism in the double hcp phase (5). The possible presence of magnetism in hcp iron as further substantiated in this article has important implications. In geophysics many experiments are carried out on potentially magnetic hcp iron and are then extrapolated to pressures of Earth's core, into the nonmagnetic region of the hcp stability field at high pressure, and may consequently not be valid. The possible presence of magnetism in hcp iron also plays an important role in the discussion of the recently observed superconductivity of hcp iron (12, 13): Magnetic correlations in hcp iron appear to be necessary to explain the observed pressure dependence of its superconductivity (14-16).The two lower-pressure polymorphs of iron are both magnetic. The phase stable around ambient conditions, body-centered cubic (bcc), owes its stability entirely to the presence of ferromagnetism (4). Heating above the Curie temperature causes the spins to disorder and the net magnetization to vanish, but the ind...

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“…Similar results were obtained for non-stoichiometric insulator Fe 1+x S [26] and many other low-spin ferrous and insulating compounds like cyanides. The situation is somewhat different for the superconducting high-pressure hexagonal -Fe [27], where the external field being able to destroy superconductivity induces a hyperfine field on the iron nucleus far beyond the limit of the Knight shift [28]. The Knight shift for the iron-based superconductors investigated up to now by 57 Fe (14.41-keV line) Mössbauer spectroscopy is below detection limit by this method.…”

Section: Discussionmentioning

confidence: 96%

Mössbauer spectroscopy evidence for the lack of iron magnetic moment in superconducting FeSe

Błachowski

Ruebenbauer

Żukrowski

et al. 2010

Journal of Alloys and Compounds

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a b s t r a c tSuperconducting FeSe has been investigated by measurements of the magnetic susceptibility versus temperature and Mössbauer spectroscopy at various temperatures including strong external magnetic fields applied to the absorber. It was found that isomer shift exhibits sharply defined increase at about 105 K leading to the lowering of the electron density on iron nucleus by 0.02 electron a.u. −3 . Above jump in the electron density is correlated with the transition from the P4/nmm to the Cmma structure, while decreasing temperature. Mössbauer measurements in the external magnetic field and for temperatures below transition to the superconducting state revealed null magnetic moment on iron atoms. Hence, the compound exhibits either Pauli paramagnetism or diamagnetic behavior. The principal component of the electric field gradient on the iron nucleus was found as negative on the iron site.

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Internal magnetic fields in hcp-iron

Abstract: The magnetic behavior of hcp-~e (epsilon iron) ha~been investi

Cited by 45 publications

References 14 publications

Non-collinear magnetism in iron at high pressures

Non-collinear magnetism in iron at high pressures

Magnetism in dense hexagonal iron

Mössbauer spectroscopy evidence for the lack of iron magnetic moment in superconducting FeSe

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