Two-dimensional magnetic interactions in LaFeAsO

Ramazanoglu, M.; Lamsal, Jagat; Tucker, G. S.; Yan, Jiaqiang; Calder, Stuart; Guidi, T.; Perring, T. G.; McCallum, R. W.; Lograsso, Thomas A.; Kreyßig, A.; Goldman, A. I.; McQueeney, R. J.

doi:10.1103/physrevb.87.140509

Cited by 19 publications

(16 citation statements)

References 24 publications

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“…The highly one-dimensional nature of the fluctuations indicate that a highly anisotropic order is proximate in the chalcogenide superconductors. The anisotropy exceeds that observed in superconducting LaFeAsO [37] and CaFe 2 As 2 in the paramagnetic phase [38]. While the the results may indicate stripe-like fluctuations, as discussed in the context of the cuprates, [39,40] [42]) given the lack of spin-wave cones and the integrated intensity discussed below.…”

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confidence: 70%

Soft striped magnetic fluctuations competing with superconductivity inFe1+xTe

et al. 2014

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Neutron spectroscopy is used to investigate the magnetic fluctuations in Fe1+xTe -a parent compound of chalcogenide superconductors. Incommensurate "stripe-like" excitations soften with increased interstitial iron concentration. The energy crossover from incommensurate to stripy fluctuations defines an apparent hour-glass dispersion. Application of sum rules of neutron scattering find that the integrated intensity is inconsistent with an S=1 Fe 2+ ground state and significantly less than S=2 predicted from weak crystal field arguments pointing towards the Fe 2+ being in a superposition of orbital states. The results suggest that a highly anisotropic order competes with superconductivity in chalcogenide systems.Pnictide and chalcogenide superconductors have altered the view of what provides the basis for high temperature superconductivity. While the cuprate superconductors universally derive from Mott insulators which can, at least qualitatively, be understood in terms of a single electronic band, the parent phase of iron based superconductors has been less clear: Fe-based parent phases are either poorly metallic or semimetallic resulting in a debate over whether a localized or itinerant/spin density wave picture is more appropriate. [1, 2] Towards this goal, it is important to understand the magnetic excitation spectrum in starting materials as superconducting variants consist of fluctuating versions of this ground state.[3] Here we study Fe 1+x Te which is arguably the structurally simplest of the iron superconductors based upon single layers of tetrahedrally coordinated Fe 2+ ions. [4, 5] While the iron superconductors have been shown to display both localized [6, 7] and itinerant properties [8, 9], Fe 1+x Te hosts one of the most localized responses of all iron based superconductors evidenced by large ordered magnetic moments and calculated heavy band masses. [10] In this study, we combine neutron scattering data from spectrometers with overlapping dynamic ranges on two samples of Fe 1+x Te to understand the magnetic fluctuations. We report a one dimensional incommensurate excitation that softens with increased charge doping with interstitial iron and hence competes with unconventional chalcogenide superconductivity. We apply sum rules of neutron scattering to evaluate the spin and orbital ground state of the iron cations. The results represent a dynamical signature of a highly anisotropic striped order which competes with superconductivity in the chalcogenides. Superconductivity in Fe 1+xTe 1−y Ch y (where Ch is a chalcogenide ion) has been most commonly achieved through anion substitution on the Te site y with either sulfur or selenium. [11, 12] However, the cation concentration (interstitial iron x) in Fe 1+x Te 1−y Ch y is directly correlated with the anion concentration (y) and chemical techniques have been developed to independently tune x and y.[13] Several studies have found that changing the concentration of interstitial iron has analogous effects to anion doping for a fixed selenium concentrat...

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Soft striped magnetic fluctuations competing with superconductivity inFe1+xTe

et al. 2014

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“…3(a), a clear energy gap ≈8 meV at (220) in the low-E region is observed at 3.5 K and the gap drops smoothly with increasing temperature. In the damped simple harmonic oscillator approximation [23][24][25], the neutron-scattering cross section is given by…”

Section: Resultsmentioning

confidence: 99%

“…In the small-q limit, the spin waves around (220) zone center can be approximately described by an anisotropic linear dispersion relation [4,23]:…”

Section: Resultsmentioning

confidence: 99%

Magnetic excitations and anomalous spin-wave broadening in multiferroic FeV2O4

et al. 2014

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We report on the different roles of two orbital-active Fe2+ at the A site and V3+ at the B site in the magnetic excitations and on the anomalous spin-wave broadening in FeV2O4. FeV2O4 exhibits three structural transitions and successive paramagnetic (PM)-collinear ferrimagnetic (CFI)-noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM-orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbitcoupling-induced anisotropy at the Fe2+ site. While there is no measurable increase in the energy gap from the orbital ordering of V3+ at the orthorhombic/CFI-tetragonal/NCFI transition, anomalous spin-wave broadening is observed in the orthorhombic/CFI state due to V3+ spin fluctuations at the B site. The spinwave broadening is also observed at the zone boundary without softening in the NCFI/ferroelectric phase, which is discussed in terms of magnon-phonon coupling. Our study also indicates that the Fe2+ spins without the frustration at the A site may not play an important role in inducing ferroelectricity in the tetragonal/NCFI phase of FeV2O4. We report on the different roles of two orbital-active Fe 2+ at the A site and V 3+ at the B site in the magnetic excitations and on the anomalous spin-wave broadening in FeV 2 O 4 . FeV 2 O 4 exhibits three structural transitions and successive paramagnetic (PM)-collinear ferrimagnetic (CFI)-noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM-orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbit-coupling-induced anisotropy at the Fe 2+ site. While there is no measurable increase in the energy gap from the orbital ordering of V 3+ at the orthorhombic/CFI-tetragonal/NCFI transition, anomalous spin-wave broadening is observed in the orthorhombic/CFI state due to V 3+ spin fluctuations at the B site. The spin-wave broadening is also observed at the zone boundary without softening in the NCFI/ferroelectric phase, which is discussed in terms of magnon-phonon coupling. Our study also indicates that the Fe 2+ spins without the frustration at the A site may not play an important role in inducing ferroelectricity in the tetragonal/NCFI phase of FeV 2 O 4 .

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“…Of the 11, 111, 122, 1111, 245 families of materials, spin waves in the AF parent compounds throughout the Brillouin zone were mapped out for the 11 (Lipscombe et al, 2011;Zaliznyak et al, 2011), 111 , 122 (Diallo et al, 2009;Ewings et al, 2011;Harriger et al, 2011;Zhao et al, 2009), and 245 (Chi et al, 2013;Wang et al, 2011c;Xiao et al, 2013) families of materials due to the availability of large single crystals needed for inelastic neutron scattering experiments. Although single crystals of the 1111 family of materials are still not large enough to allow a determination of the entire spin wave spectra, measurements of low-energy spin waves reveal that the system is highly two-dimensional with weak magnetic exchange coupling along the c axis (Ramazanoglu et al, 2013). In the Sections III A and B, we describe spin wave measurements in the parent compounds of different families of iron-based superconductors and discuss their relationship with superconductivity.…”

Section: Spin Excitations and Their Relationship With Supercondumentioning

confidence: 99%

Antiferromagnetic order and spin dynamics in iron-based superconductors

2015

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High-transition temperature (high-Tc) superconductivity in the iron pnictides/chalcogenides emerges from the suppression of the static antiferromagnetic order in their parent compounds, similar to copper oxides superconductors. This raises a fundamental question concerning the role of magnetism in the superconductivity of these materials. Neutron scattering, a powerful probe to study the magnetic order and spin dynamics, plays an essential role in determining the relationship between magnetism and superconductivity in high-Tc superconductors. The rapid development of modern neutron time-of-flight spectrometers allows a direct determination of the spin dynamical properties of iron-based superconductors throughout the entire Brillouin zone. In this review, we present an overview of the neutron scattering results on iron-based superconductors, focusing on the evolution of spin excitation spectra as a function of electron/hole-doping and isoelectronic substitution. We compare spin dynamical properties of iron-based superconductors with those of copper oxide and heavy fermion superconductors, and discuss the common features of spin excitations in these three families of unconventional superconductors and their relationship with superconductivity.

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Two-dimensional magnetic interactions in LaFeAsO

Cited by 19 publications

References 24 publications

Soft striped magnetic fluctuations competing with superconductivity inFe1+xTe

Soft striped magnetic fluctuations competing with superconductivity inFe1+xTe

Magnetic excitations and anomalous spin-wave broadening in multiferroic FeV2O4

Antiferromagnetic order and spin dynamics in iron-based superconductors

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