Spin Excitation Anisotropy as a Probe of Orbital Ordering in the Paramagnetic Tetragonal Phase of Superconducting<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>BaFe</mml:mi><mml:mn>1.904</mml:mn></mml:msub><mml:msub><mml:mi>Ni</mml:mi><mml:mn>0.096</mml:mn></mml:msub><mml:msub><mml:mi>As</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>

Luo, Huiqian; Wang, Meng; Zhang, Chenglin; Lu, Xiaochen; Regnault, L.P.; Zhang, Rui; Li, Shiliang; Hu, Jiangping; Dai, Pengcheng

doi:10.1103/physrevlett.111.107006

Cited by 64 publications

(104 citation statements)

References 34 publications

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“…The spin reorientation observed in Ba 1-x Na x Fe 2 As 2 is in agreement with the anisotropies found in pure and in doped BaFe 2 As 2 [18,19,23]. The analysis of the gaps of magnetic excitations in pure BaFe 2 As 2 indicates that rotating the moment into the c direction corresponds to the lower anisotropy energy in contrast to the expectation for a layered magnet.…”

Section: Pacs Numberssupporting

confidence: 62%

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Spin reorientation inBa0.65Na0.35Fe2As2studied by single-crystal neutron diffraction

et al. 2015

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We have studied the magnetic ordering in Na doped BaFe2As2 by unpolarized and polarized neutron diffraction using single crystals. Unlike previously studied FeAs-based compounds that magnetically order, Ba1−xNaxFe2As2 exhibits two successive magnetic transitions: For x=0.35 upon cooling magnetic order occurs at ∼70 K with in-plane magnetic moments being arranged as in pure or Ni, Co and K-doped BaFe2As2 samples. At a temperature of ∼46 K a second phase transition occurs, which the single-crystal neutron diffraction experiments can unambiguously identify as a spin reorientation. At low temperatures, the ordered magnetic moments in Ba0.65Na0.35Fe2As2 point along the c direction. Magnetic correlations in these materials cannot be considered as Ising like, and spin-orbit coupling must be included in a quantitative theory. PACS numbers:There are two promising explanations for the appearance of high-temperature superconductivity in FeAsbased materials [1]. Orbital fluctuations may result in a s ++ superconducting state [2,3] and can reflect the fact that highest superconducting transition temperatures arise in materials with almost ideal FeAs 4 tetrahedrons [4] and, thus, with highest orbital degeneracy. On the other hand, there are strong magnetic fluctuations associated with the antiferromagnetic (AFM) order in the parent compounds which can explain a s ± superconducting state [5].Magnetism and orbital degrees of freedom are closely tied in FeAs-based compounds. Although the structural distortion accompanying AFM order in the parent materials remains small [6][7][8] its electronic signatures are rather strong as seen in the anisotropic resistance [9,10], in angle-resolved photoemission studies (ARPES) [11,12] or optical spectroscopy [13]. In addition the magnon dispersion in the AFM state is fully anisotropic [14] inspiring theoretical models of orbital order driving magnetic interaction similar to those applied to manganates [15][16][17]. Studying the interplay between orbital and magnetic degrees of freedom seems crucial for the understanding of FeAs-based materials.Here we focus on spin-space anisotropies arising from the spin-orbit coupling between spin and orbital moments and which thus allow for a direct view on orbital contributions. In AFM BaFe 2 As 2 , polarized neutron scattering shows that it costs more energy to rotate the magnetic moment within the planes than perpendicular to them [18]. Magnetic anisotropy clearly persists into the superconducting range of the phase diagrams [19][20][21][22][23].So far all AFM ordered FeAs-based compounds exhibit a single magnetic transition to a magnetic structure where moments are aligned parallel to the in-plane

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Section: Pacs Numberssupporting

confidence: 62%

“…In AFM BaFe 2 As 2 , polarized neutron scattering shows that it costs more energy to rotate the magnetic moment within the planes than perpendicular to them [18]. Magnetic anisotropy clearly persists into the superconducting range of the phase diagrams [19][20][21][22][23].…”

Section: Pacs Numbersmentioning

confidence: 99%

Spin reorientation inBa0.65Na0.35Fe2As2studied by single-crystal neutron diffraction

et al. 2015

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“…A possible cause for this difference is that whereas divergent longitudinal fluctuations in BaFe 2 As 2 just above T N have M a > M b ≈ M c [57], anisotropic fluctuations in the normal state of BaFe 2 As 2 -derived superconductors near optimal doping exhibit M a ≈ M c > M b [34,52]. The differing character of polarization may account for the different effects on the nematic susceptibility.…”

Section: Discussionmentioning

confidence: 92%

“…It is noteworthy that anisotropic fluctuations typically appear above T c [Figs. 7(c) and 7(e)], and develop into an anisotropic resonance mode or become partially gapped inside the superconducting state [34][35][36][37]42,52]. BaFe 2 As 1.4 P 0.6 appears to be an exception, with anisotropic spin fluctuations only present in the superconducting state [44].…”

Section: Discussionmentioning

confidence: 99%

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Temperature and polarization dependence of low-energy magnetic fluctuations in nearly optimally doped NaFe0.9785Co0.0215As

et al. 2017

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We use unpolarized and polarized neutron scattering to study the temperature and polarization dependence of low-energy magnetic fluctuations in nearly optimally doped NaFe 0.9785 Co 0.0215 As, with coexisting superconductivity (T c ≈ 19 K) and weak antiferromagnetic order (T N ≈ 30 K, ordered moment ≈0.02 μ B /Fe). A single spin resonance mode with intensity tracking the superconducting order parameter is observed, although energy of the mode only softens slightly upon approaching T c . Polarized neutron scattering reveals that the single resonance is mostly isotropic in spin space, similar to overdoped NaFe 0.935 Co 0.045 As but different from optimal electron-, hole-, and isovalently doped BaFe 2 As 2 compounds, all featuring an additional prominent anisotropic component. Spin anisotropy in NaFe 0.9785 Co 0.0215 As is instead present at energies below the resonance, which becomes partially gapped below T c , similar to the situation in optimally doped YBa 2 Cu 3 O 6.9 . Our results indicate that anisotropic spin fluctuations in NaFe 1−x Co x As appear in the form of a resonance in the underdoped regime, become partially gapped below T c near optimal doping, and disappear in overdoped compounds.

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Spin reorientation transition in Na‐doped BaFe₂As₂ studied by single‐crystal neutron diffraction

Waßer

Wurmehl

Aswartham

et al. 2016

Physica Status Solidi (b)

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Several hole‐doped BaFe2As2 compounds were recently shown to exhibit a second magnetic phase transition in the concentration range close to the full suppression of antiferromagnetic (AFM) order. At this additional transition ordered magnetic moments reorient from in‐plane to out‐of‐plane alignment associated with a suppression of the orthorhombic distortion. We have studied the magnetic properties of such a representative hole‐doped system, Ba1–xNaxFe2As2 with 0.25 ≤ x ≤ 0.40, by neutron diffraction on large single crystals. With increasing Na substitution (0.25 ≤ x ≤ 0.39) the AFM transition temperature sharply decreases, while the spin‐reorientation transition temperature is rather constant, until both magnetic phases are completely suppressed at x = 0.40. For all studied Na concentrations the additional transition is related to the spin reorientation, which, however, is complete only in the middle of the concentration range of the out‐of‐plane phase. In the superconducting state, the intensities of magnetic Bragg reflections become heavily suppressed; this effect seems to increase for larger Tc and reaches ∼50% in Ba0.61Na0.39Fe2As2. In samples with coexisting in‐plane and out‐of‐plane ordering, this superconductivity induced suppression of ordered moments is significantly stronger for the out‐of‐plane components indicating that this phase more strongly competes with superconductivity.

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Spin Excitation Anisotropy as a Probe of Orbital Ordering in the Paramagnetic Tetragonal Phase of SuperconductingBaFe1.904Ni0.096As2

Cited by 64 publications

References 34 publications

Spin reorientation inBa0.65Na0.35Fe2As2studied by single-crystal neutron diffraction

Spin reorientation inBa0.65Na0.35Fe2As2studied by single-crystal neutron diffraction

Temperature and polarization dependence of low-energy magnetic fluctuations in nearly optimally doped NaFe0.9785Co0.0215As

Spin reorientation transition in Na‐doped BaFe₂As₂ studied by single‐crystal neutron diffraction

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Spin Excitation Anisotropy as a Probe of Orbital Ordering in the Paramagnetic Tetragonal Phase of SuperconductingBaFe1.904Ni0.096As2

Cited by 64 publications

References 34 publications

Spin reorientation inBa0.65Na0.35Fe2As2studied by single-crystal neutron diffraction

Spin reorientation inBa0.65Na0.35Fe2As2studied by single-crystal neutron diffraction

Temperature and polarization dependence of low-energy magnetic fluctuations in nearly optimally doped NaFe0.9785Co0.0215As

Spin reorientation transition in Na‐doped BaFe2As2 studied by single‐crystal neutron diffraction

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Spin reorientation transition in Na‐doped BaFe₂As₂ studied by single‐crystal neutron diffraction