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Journal ArticleDOI

Evidence of a structural phase transition in superconducting SmFeAsO 1-x F x from 19 F NMR

16 Jan 2013-Journal of Physics: Condensed Matter (IOP Publishing)-Vol. 25, Iss: 2, pp 025701
TL;DR: The resistivity, magnetization and (19)F NMR results in a polycrystalline sample of SmFeAsO indicate the existence of a structural phase transition near 163 K in the sample, which also undergoes a superconducting transition.
Abstract: We report resistivity, magnetization and 19F NMR results in a polycrystalline sample of SmFeAsO0.86F0.14. The resistivity and magnetization data show a sharp drop at 48 K indicating a superconducting transition. The nuclear spin–lattice rate (1/T1) and spin–spin relaxation rate (1/T2) clearly show the existence of a structural phase transition near 163 K in the sample, which also undergoes a superconducting transition. This finding creates interest in exploring whether this is unique for Sm based systems or is also present in other rare-earth based 1111 superconductors.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a detailed review of phase diagrams for iron-based superconductors is presented, with the most studied 11-, 122-and 1111-type compound systems provided a correlation between experimental evidence and theory.

63 citations

Journal ArticleDOI
TL;DR: In this paper, the lattice properties at low temperatures of two samples of NdFeAsO1-xFx (x = 0.05 and 0.25) have been examined in order to investigate possible structural phase transition that may occur in the optimally doped superconducting sample with respect to the non-superconducting low-F concentration compound.
Abstract: The lattice properties at low temperatures of two samples of NdFeAsO1-xFx (x = 0.05 and 0.25) have been examined in order to investigate possible structural phase transition that may occur in the optimally doped superconducting sample with respect to the non-superconducting low-F concentration compound. In order to detect small modifications in the ion displacements with temperature micro-Raman and high resolution synchrotron powder diffraction measurements were carried out. No increase of the width of the (2 2 0) or (3 2 2) tetragonal diffraction peaks and microstrains could be found in the superconducting sample from synchrotron XRD measurements. On the other hand, the atomic displacement parameters deviate from the expected behavior, in agreement with modifications in the phonon width, as obtained by Raman scattering. These deviations occur around 150 K for both F dopings, with distinct differences among the two compounds, i.e., they decrease at low doping and increase for the superconducting sample. The data do not support a hidden phase transition to an orthorhombic phase in the superconducting compound, but point to an isostructural lattice deformation. Based on the absence of magnetic effects in this temperature range for the superconducting sample, we attribute the observed lattice anomalies to the formation of local lattice distortions that, being screened by the carriers, can only acquire long-range coherence by means of a structural phase transition at low doping levels. (C) 2016 Elsevier B.V. All rights reserved.

21 citations

Journal ArticleDOI
TL;DR: Direct comparison between the magnetic and structural properties indicates that the magnetic transition is always associated with structural symmetry breaking, although confined to a local scale at high Ru contents.
Abstract: Structural refinement, lattice micro-strain and spontaneous strain analyses have been carried out on selected members of the La(Fe1-xRux)AsO system using high-resolution neutron and synchrotron powder diffraction data. The obtained results indicate that the character of the tetragonal to orthorhombic structural transition changes from first order for x = 0.10, possibly to tricritical for x = 0.20, up to second order for x = 0.30; for x ≥ 0.40 symmetry breaking is suppressed, even though a notable increase of the lattice micro-strain develops at low temperature. By combining structural findings with previous muon spin rotation data, a phase diagram of the La(Fe1-xRux)AsO system has been drawn. Long-range ordered magnetism occurs within the orthorhombic phase (x ≤ 0.30), whereas short-range magnetism appears to be confined within the lattice strained region of the tetragonal phase up to x < 0.60. Direct comparison between the magnetic and structural properties indicates that the magnetic transition is always associated with structural symmetry breaking, although confined to a local scale at high Ru contents.

7 citations

Journal ArticleDOI
TL;DR: Using the self-consistent renormalization (SCR) theory of itinerant ferromagnets, it is shown that in the ab plane, the spin fluctuations are three-dimensional ferromagnetic in nature.
Abstract: 75As and 31P NMR studies are performed in PrCoAsO and NdCoPO respectively. The Knight shift data in PrCoAsO indicate the presence of an antiferromagnetic interaction between the 4f moments along the c axis in the ferromagnetic state of Co 3d moments. We propose a possible spin structure in this system. The 75As quadrupolar coupling constant, νQ, increases continuously with decrease of temperature and is found to vary linearly with the intrinsic spin susceptibility, Kiso. This indicates the possibility of the presence of a coupling between charge density and spin density fluctuations. Further, the 31P NMR Knight shift and spin–lattice relaxation rate (1/T1) in the paramagnetic state of NdCoPO indicate that the differences of LaCoPO and NdCoPO from SmCoPO are due to the decrement of the interlayer separation and not due to the moments of the 4f electrons. The nuclear spin–lattice relaxation time (T1) in NdCoPO shows weak anisotropy at 300 K. Using the self-consistent renormalization (SCR) theory of itinerant ferromagnets, it is shown that in the ab plane, the spin fluctuations are three-dimensional ferromagnetic in nature. From SCR theory the important spin-fluctuation parameters (T0, TA, ) are evaluated. The similarities and dissimilarities of the NMR results in As and P based systems with different rare earths are also discussed.

6 citations

01 Oct 2009
TL;DR: In this article, a new lattice framework is proposed to extract the relevant gluonic energy scale of QCD phenomena which is based on a 'cut' on link variables in momentum space.
Abstract: We propose a new lattice framework to extract the relevant gluonic energy scale of QCD phenomena which is based on a 'cut' on link variables in momentum space. This framework is expected to be broadly applicable to all lattice QCD calculations. Using this framework, we quantitatively determine the relevant energy scale of color confinement, through the analyses of the quark-antiquark potential and meson masses. The relevant energy scale of color confinement is found to be below 1.5 GeV in the Landau gauge. In fact, the string tension is almost unchanged even after cutting off the high-momentum gluon component above 1.5 GeV. When the relevant low-energy region is cut, the quark-antiquark potential is approximately reduced to a Coulomb-like potential, and each meson becomes a quasifree quark pair. As an analytical model calculation, we also investigate the dependence of the Richardson potential on the cut, and find the consistent behavior with the lattice result.

3 citations

References
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Journal ArticleDOI
TL;DR: In this article, the main formulas governing the analysis of the Bragg magnetic scattering are summarized and shortly discussed and the method of profile fitting without a structural model to get precise integrated intensities and refine the propagation vector(s) of the magnetic structure is discussed.
Abstract: In spite of intrinsic limitations, neutron powder diffraction is, and will still be in the future, the primary and most straightforward technique for magnetic structure determination. In this paper some recent improvements in the analysis of magnetic neutron powder diffraction data are discussed. After an introduction to the subject, the main formulas governing the analysis of the Bragg magnetic scattering are summarized and shortly discussed. Next, we discuss the method of profile fitting without a structural model to get precise integrated intensities and refine the propagation vector(s) of the magnetic structure. The simulated annealing approach for magnetic structure determination is briefly discussed and, finally, some features of the program FullProf concerning the magnetic structure refinement are presented and discussed. The different themes are illustrated with simple examples.

11,923 citations

Journal ArticleDOI
TL;DR: The response of the worldwide scientific community to the discovery in 2008 of superconductivity at T c'='26'K in the Fe-based compound LaFeAsO1−x F x has been very enthusiastic.
Abstract: The response of the worldwide scientific community to the discovery in 2008 of superconductivity at T c = 26 K in the Fe-based compound LaFeAsO1−x F x has been very enthusiastic. In short order, ot...

1,373 citations

01 Jan 1985

1,302 citations


"Evidence of a structural phase tran..." refers background in this paper

  • ...This implies dominant contribution of localized Sm 4f spin-fluctuation on the 1/T1 and 1/T2 processes [17, 18]....

    [...]

Journal ArticleDOI
13 Aug 2010-Science
TL;DR: It is revealed that the representative iron arsenide Ba(Fe1−xCox)2As2 develops a large electronic anisotropy at this transition via measurements of the in-plane resistivity of detwinned single crystals, with the resistivity along the shorter b axis ρb being greater than ρa.
Abstract: High-temperature superconductivity often emerges in the proximity of a symmetry-breaking ground state. For superconducting iron arsenides, in addition to the antiferromagnetic ground state, a small structural distortion breaks the crystal’s C 4 rotational symmetry in the underdoped part of the phase diagram. We reveal that the representative iron arsenide Ba(Fe 1 −x Co x ) 2 As 2 develops a large electronic anisotropy at this transition via measurements of the in-plane resistivity of detwinned single crystals, with the resistivity along the shorter b axis ρ b being greater than ρ a . The anisotropy reaches a maximum value of ~2 for compositions in the neighborhood of the beginning of the superconducting dome. For temperatures well above the structural transition, uniaxial stress induces a resistivity anisotropy, indicating a substantial nematic susceptibility.

627 citations

Journal ArticleDOI
TL;DR: In this article, a spin S quantum Heisenberg model on the Fe lattice of the rare-earth oxypnictide superconductors was studied, and it was shown that this model exhibits a sequence of two phase transitions: from a high-temperature symmetric pha
Abstract: We study a spin S quantum Heisenberg model on the Fe lattice of the rare-earth oxypnictide superconductors. Using both large S and large N methods, we show that this model exhibits a sequence of two phase transitions: from a high-temperature symmetric pha

450 citations