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Title: Electronic properties of LaO1-xFxFeAs in the normal state probed by nmr/nqr
Authors: Grafe, H.-J.Lang, G.Hammerath, F.Paar, D.Manthey, K.Koch, K.Rosner, H.Curro, N. J.Behr, G.Werner, J.
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Issue Date: 2009
Published in: New Journal of Physics, Volume 12
Publisher: Milton Park : Taylor & Francis
Abstract: We report 139La, 57Fe and 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on powders of the new LaO1−xFxFeAs superconductor for x=0 and 0.1 at temperatures up to 480 K, and compare our measured NQR spectra with local density approximation (LDA) calculations. For all three nuclei in the x=0.1 material, it is found that the local Knight shift increases monotonically with an increase in temperature, and scales with the macroscopic susceptibility, suggesting a single magnetic degree of freedom. Surprisingly, the spin lattice relaxation rates for all nuclei also scale with one another, despite the fact that the form factors for each site sample different regions of q-space. This result suggests a lack of any q-space structure in the dynamical spin susceptibility that might be expected in the presence of antiferromagnetic correlations. Rather, our results are more compatible with simple quasi-particle scattering. Furthermore, we find that the increase in the electric field gradient at the As cannot be accounted for by LDA calculations, suggesting that structural changes, in particular the position of the As in the unit cell, dominate the NQR response.
Keywords: Antiferromagnetic correlations; Electric field gradients; Form factors; Knight shifts; Local density-approximation; Magnetic degrees; NMR/NQRNormal state; Nuclear quadrupole resonance measurements; Q spaces; Quasi particles; Spin susceptibilities; Spin-lattice relaxation rates; Structural changes; Unit cells
DDC: 530
License: CC BY-NC-SA 3.0 Unported
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