Commensurate Itinerant Antiferromagnetism in BaFe2As2: 75As-NMR Studies on a Self-Flux Grown Single Crystal

Kitagawa, Kentaro; Katayama, Naoyuki; Ohgushi, Kenya; Yoshida, Makoto; Takigawa, Masaharu

doi:10.1143/jpsj.77.114709

Cited by 278 publications

(508 citation statements)

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Section: Nmrmentioning

confidence: 99%

“…Such a spectrum proves a quasi-static and spatially disordered field distribution in NaCaCo 2 F 7 . Collinear and non-collinear long-range ordered states can be ruled out, because in single crystals those would induce a distinct line splitting in the ordered state [18][19][20].Analysis of the 23 Na NMR spectra 23 Na NMR spectra were taken on the geodesic between (1 1 1) and (1 0 0) directions. To describe the data, a physical model is constructed, by taking into account the crystal structure and the nearest neighbors environments.…”

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Spin freezing in the disordered pyrochlore magnet NaCaCo2F7 : NMR studies and Monte Carlo simulations

et al. 2017

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We present results of 23 Na and 19 F nuclear magnetic resonance (NMR) measurements on NaCaCo2F7, a frustrated pyrochlore magnet with a Curie-Weiss temperature, ΘCW ≈ −140 K, and intrinsic bond disorder. Below 3.6 K both the 23 Na and 19 F spectra broaden substantially in comparison to higher temperatures accompanied by a considerable reduction (80 %) of the NMR signal intensity: This proves a broad quasi-static field distribution. The 19 F spin-lattice relaxation rate 19 (1/T1) exhibits a peak at 2.9 K already starting to develop below 10 K. We attribute the spin freezing to the presence of bond disorder. This is corroborated by large-scale Monte-Carlo simulations of a classical bond-disordered XY model on the pyrochlore lattice. The low freezing temperature, together with the very short magnetic correlation length not captured by the simulations, suggesting that quantum effects play a decisive role in NaCaCo2F7.PACS numbers: 75.10. Nr, 75.40.Gb, The pyrochlore lattice is one of the canonical lattices exhibiting geometric frustration. Pyrochlore oxides with the general formula R 2 T 2 O 7 (R = rare earth ion, T = Ti, Sn, Mo, Ir etc.) are characterized by strong frustration of the rare-earth magnetic moments and have been found to display a variety of fascinating low-temperature phases, including classical and quantum spin-ice regimes, quantum order-by-disorder, and exotic spin liquids [1][2][3].NaCaCo 2 F 7 is a recently synthesized A 2 B 2 X 7 -type pyrochlore [4]. Here, the B site hosts high-spin Co 2+ in CoF 6 octahedra, whereas the A site contains a random distribution of Na and Ca ions, giving rise to exchange (bond) disorder for the magnetic degrees of freedom. Bond disorder can lift degeneracies and lead to new unconventional ground states, both long-range ordered [5,6] and glassy [7][8][9][10].The uniform susceptibility of NaCaCo 2 F 7 displays a Curie-Weiss law with a characteristic temperature Θ CW ≈ −140 K and a moment of 6.1 µ B per Co, the latter suggesting an orbital contribution in addition to the S = 3/2 state of Co 2+ . Despite the Θ CW ≈ −140 K, the material does not display a long-range-ordered magnetic state down to temperatures of 0.6 K [4]. Instead, ac and dc susceptibility data indicate a spin freezing at T f ≈ 2.4 K [4], yielding a frustration index of f = Θ CW /T f ≈ 56. The observed entropy loss at the freezing transition is low, suggesting that magnetic entropy remains present at least down to 0.6 K. Inelastic neutron scattering (INS) results [11] for NaCaCo 2 F 7 show diffuse elastic scattering below 2.4 K. The momentum-space structure of the spin correlations below 2.5 meV has been interpreted in terms of XY-like antiferromagnetic clusters, indicating a local easy-plane anisotropy at low energies, whereas a signal corresponding to collinear correlations was found above this energy. The XY character together with the short detected correlation length of 16Å [11] appears to be at odds with the theoretical suggestion [6] that bond disorder in an XY pyrochlore magnet induces long-range m...

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Section: Nmrmentioning

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Spin freezing in the disordered pyrochlore magnet NaCaCo2F7 : NMR studies and Monte Carlo simulations

et al. 2017

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“…By using a hyperfine coupling constant of 1.88 T per m B obtained in the undoped parent compound 17 , the averaged ordered magnetic moment /SS is deduced. As seen in Fig.…”

Section: Electrical Resistivity Measurementsmentioning

confidence: 99%

“…Such change was indeed confirmed in the parent compounds BaFe 2 As 2 (ref. 17) and LaFeAsO (ref. 27).…”

Section: Electrical Resistivity Measurementsmentioning

confidence: 99%

Quantum criticality in electron-doped BaFe2−xNixAs2

et al. 2013

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A quantum critical point is a point in a system's phase diagram at which an order is completely suppressed at absolute zero temperature (T). The presence of a quantum critical point manifests itself in the finite-T physical properties, and often gives rise to new states of matter. Superconductivity in the cuprates and in heavy fermion materials is believed by many to be mediated by fluctuations associated with a quantum critical point. In the recently discovered iron-pnictide superconductors, we report transport and NMR measurements on BaFe 2 À x Ni x As 2 (0rxr0.17). We find two critical points at x c1 ¼ 0.10 and x c2 ¼ 0.14. The electrical resistivity follows r ¼ r 0 þ AT n , with n ¼ 1 around x c1 and another minimal n ¼ 1.1 at x c2 . By NMR measurements, we identity x c1 to be a magnetic quantum critical point and suggest that x c2 is a new type of quantum critical point associated with a nematic structural phase transition. Our results suggest that the superconductivity in carrier-doped pnictides is closely linked to the quantum criticality.

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“…In the AFM state of iron pnictides, it was reported that Fe ordered moments lying in the ab plane with stripe correlations induce an internal magnetic field H int along the c-axis at the As and P sites owing to the off-diagonal term of the hyperfine coupling tensor. 23,24) In such a commensurate stripe-type AFM ordered state, the powder pattern of I = 1/2 becomes nearly rectangular. 25) However, the obtained spectra show a Lorentzian-like shape, indicative of the distribution of H int .…”

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Relationship between Superconductivity and Antiferromagnetism in LaFe(As₁₋_xP_x)O Revealed by ³¹P-NMR

et al. 2014

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Commensurate Itinerant Antiferromagnetism in BaFe₂As₂: ⁷⁵As-NMR Studies on a Self-Flux Grown Single Crystal

Cited by 278 publications

References 15 publications

Spin freezing in the disordered pyrochlore magnet NaCaCo2F7 : NMR studies and Monte Carlo simulations

Spin freezing in the disordered pyrochlore magnet NaCaCo2F7 : NMR studies and Monte Carlo simulations

Quantum criticality in electron-doped BaFe2−xNixAs2

Relationship between Superconductivity and Antiferromagnetism in LaFe(As₁₋_xP_x)O Revealed by ³¹P-NMR

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Commensurate Itinerant Antiferromagnetism in BaFe2As2: 75As-NMR Studies on a Self-Flux Grown Single Crystal

Cited by 278 publications

References 15 publications

Spin freezing in the disordered pyrochlore magnet NaCaCo2F7 : NMR studies and Monte Carlo simulations

Spin freezing in the disordered pyrochlore magnet NaCaCo2F7 : NMR studies and Monte Carlo simulations

Quantum criticality in electron-doped BaFe2−xNixAs2

Relationship between Superconductivity and Antiferromagnetism in LaFe(As1−xPx)O Revealed by 31P-NMR

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Commensurate Itinerant Antiferromagnetism in BaFe₂As₂: ⁷⁵As-NMR Studies on a Self-Flux Grown Single Crystal

Relationship between Superconductivity and Antiferromagnetism in LaFe(As₁₋_xP_x)O Revealed by ³¹P-NMR