Structure antiferroma gnetique de Fe1. 125Te accompagnee d'une deformation monoclinique

We review neutron scattering investigations of the crystal structures, magnetic structures, and spin dynamics of the iron-based RFe(As,P)O (R=La, Ce, Pr, Nd), (Ba,Sr,Ca)Fe 2 As 2 , and Fe 1+x (Te-Se) systems. On cooling from room temperature all the undoped materials exhibit universal behavior, where a tetragonal-to-orthorhombic/monoclinic structural transition occurs, below which the systems become antiferromagnets. For the first two classes of materials the magnetic structure within the a-b plane consists of chains of parallel Fe spins that are coupled antiferromagnetically in the orthogonal direction, with an ordered moment typically less than one Bohr magneton. Hence these are itinerant electron magnets, with a spin structure that is consistent with Fermi-surface nesting and a very energetic spin wave bandwidth ~0.2 eV. With doping, the structural and magnetic transitions are suppressed in favor of superconductivity, with superconducting transition temperatures up to ≈55 K. Magnetic correlations are observed in the superconducting regime, with a magnetic resonance that follows the superconducting order parameter just like the cuprates. The rare-earth moments order antiferromagnetically at low T like 'conventional' magnetic-superconductors, while the Ce crystal field linewidths are affected when superconductivity sets in. The application of pressure in CaFe 2 As 2 transforms the system from a magnetically ordered orthorhombic material to a 'collapsed' non-magnetic tetragonal system. Tetragonal Fe 1+x Te transforms to a low T monoclinic structure at small x that changes to orthorhombic at larger x, which is accompanied by a crossover from commensurate to incommensurate magnetic order.Se doping suppresses the magnetic order, while incommensurate magnetic correlations are observed in the superconducting regime.

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“…The (known) crystal structures at room temperature are all tetragonal [5][6][7][8][9], and are shown in Fig. 1.…”

Section: Crystal and Magnetic Structuresmentioning

confidence: 99%

“…For the Fe 1+x (Te-Se) system [9,[30][31][32][33], crystallographically there are two iron sites, one of which is partially occupied, while the (Te, Se) site is fully occupied. Hence the composition should be indicated as Fe 1+x (Te,Se).…”

Section: Fe 1+x (Te-se) Systemmentioning

confidence: 99%

Neutron studies of the iron-based family of high TC magnetic superconductors

Lynn

Dai

2009

Physica C: Superconductivity

154

163

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“…However, pure FeTe is not superconducting and the two end compounds of the "11" solid solution, FeSe and FeTe, even if structurally isomorphic, reveal to be substantially different. Both are off-stoichiometric, but whereas the off-stoichiometry in FeSe 1−y is preferably ascribed to Se-deficiency [11,12,13], in Fe 1+x Te excess Fe atoms occupy an additional site in the Fe-Te plane [14,15,16]. In Fe 1+x Te both magnetic (AFM) and structural (tetragonal to monoclinic) transitions occur at the same temperature T N 67 K [14], with the propagation vector aligned at 45 • from the nesting vector [17].…”

Section: Introductionmentioning

confidence: 99%

“…Both are off-stoichiometric, but whereas the off-stoichiometry in FeSe 1−y is preferably ascribed to Se-deficiency [11,12,13], in Fe 1+x Te excess Fe atoms occupy an additional site in the Fe-Te plane [14,15,16]. In Fe 1+x Te both magnetic (AFM) and structural (tetragonal to monoclinic) transitions occur at the same temperature T N 67 K [14], with the propagation vector aligned at 45 • from the nesting vector [17]. In the similar compound FeSe 1−y , however, only the structural transition (tetragonal to orthorhombic) occurs between 70 and 100 K and no magnetic ordering is observed at low temperature [11,12,13,18].…”

Section: Introductionmentioning

confidence: 99%

Effect of Fe excess on structural, magnetic and superconducting properties of single-crystalline Fe1+xTe1−ySey

Viennois

Giannini

Marel

et al. 2010

Journal of Solid State Chemistry

119

137

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Single crystals of Fe 1+x Te 1−y Se y have been grown with a controlled Fe excess and Se doping, and the crystal structure has been refined for various compositions. The systematic investigation of magnetic and superconducting properties as a function of the structural parameters shows how the material can be driven into various ground states, depending on doping and the structural modifications. Our results prove that the occupation of the additional Fe site, Fe2, enhances the spin localization. By reducing the excess Fe, the antiferromagnetic ordering is weakened, and the superconducting ground state is favored. We have found that both Fe excess and Se doping in synergy determine the properties of the material and an improved 3-dimensional phase diagram is proposed.

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“…We define the coefficients for NN biquadratic exchange, λ 1 ≡ λ 12,12 = λ 14,14 = λ 23,23 = λ 34,34 ; NNN biquadratic exchange, λ 2 ≡ λ 13,13 = λ 24,24 ; NN ring exchange [38] λ 3 = λ 12,34 = λ 14,32 ; and λ 4 = λ 13,24 involving a "diagonal" ring exchange.…”

Section: A Modelmentioning

confidence: 99%

Emergent Ising degrees of freedom above a double-stripe magnetic ground state

Zhang

Flint

2017

Phys. Rev. B

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Double-stripe magnetism [ Q = ( π / 2 , π / 2 ) ] has been proposed as the magnetic ground state for both the iron-telluride and BaTi 2 Sb 2 O families of superconductors. Double-stripe order is captured within a J 1 − J 2 − J 3 Heisenberg model in the regime J 3 ≫ J 2 ≫ J 1 . Intriguingly, besides breaking spin-rotational symmetry, the ground-state manifold has three additional Ising degrees of freedom associated with bond ordering. Via their coupling to the lattice, they give rise to an orthorhombic distortion and to two nonuniform lattice distortions with wave vector ( π , π ) . Because the ground state is fourfold degenerate, modulo rotations in spin space, only two of these Ising bond order parameters are independent. Here, we introduce an effective field theory to treat all Ising order parameters, as well as magnetic order, and solve it within a large-N limit. All three transitions, corresponding to the condensations of two Ising bond order parameters and one magnetic order parameter are simultaneous and first order in three dimensions, but lower dimensionality, or equivalently weaker interlayer coupling, and weaker magnetoelastic coupling can split the three transitions, and in some cases allows for two separate Ising phase transitions above the magnetic one. Double-stripe magnetism [Q = (π/2,π/2)] has been proposed as the magnetic ground state for both the iron-telluride and BaTi 2 Sb 2 O families of superconductors. Double-stripe order is captured within a J 1 -J 2 -J 3 Heisenberg model in the regime J 3 J 2 J 1 . Intriguingly, besides breaking spin-rotational symmetry, the ground-state manifold has three additional Ising degrees of freedom associated with bond ordering. Via their coupling to the lattice, they give rise to an orthorhombic distortion and to two nonuniform lattice distortions with wave vector (π,π). Because the ground state is fourfold degenerate, modulo rotations in spin space, only two of these Ising bond order parameters are independent. Here, we introduce an effective field theory to treat all Ising order parameters, as well as magnetic order, and solve it within a large-N limit. All three transitions, corresponding to the condensations of two Ising bond order parameters and one magnetic order parameter are simultaneous and first order in three dimensions, but lower dimensionality, or equivalently weaker interlayer coupling, and weaker magnetoelastic coupling can split the three transitions, and in some cases allows for two separate Ising phase transitions above the magnetic one. Disciplines Condensed Matter Physics

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Structure antiferroma gnetique de Fe1. 125Te accompagnee d'une deformation monoclinique

Cited by 112 publications

References 9 publications

Neutron studies of the iron-based family of high TC magnetic superconductors

Neutron studies of the iron-based family of high TC magnetic superconductors

Effect of Fe excess on structural, magnetic and superconducting properties of single-crystalline Fe1+xTe1−ySey

Emergent Ising degrees of freedom above a double-stripe magnetic ground state

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