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Crossover from commensurate to incommensurate antiferromagnetism in stoichiometric NaFeAs revealed by single-crystal 23Na,75As-NMR experiments
We report results of 23Na and 75As nuclear magnetic resonance (NMR)
experiments on a self-flux grown high-quality single crystal of stoichiometric
NaFeAs. The NMR spectra revealed a tetragonal to twinned-orthorhombic
structural phase transition at T_O = 57 K and an antiferromagnetic (AF)
transition at T_AF = 45 K. The divergent behavior of nuclear relaxation rate
near T_AF shows significant anisotropy, indicating that the critical slowing
down of stripe-type AF fluctuations are strongly anisotropic in spin space. The
NMR spectra at low enough temperatures consist of sharp peaks showing a
commensurate stripe AF order with a small moment \sim 0.3 muB. However, the
spectra just below T_AF exhibits highly asymmetric broadening pointing to an
incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs
shows a certain similarity to the behavior of SrFe2As2 under high pressure.Comment: 5 pages, 5 figures, revised version to appear in J. Phys. Soc. Jp
Incipient reproductive isolation between Drosophila nasuta and Drosophila albomicans
International audienc
Non-magnetic pair-breaking effect on La(Fe_{1-x}Zn_{x})AsO_{0.85} studied by NMR and NQR
As and La NMR and nuclear quadrupole resonance (NQR) studies
on Zn-substituted LaFeAsO have been performed to investigate the
Zn-impurity effects microscopically. Although superconductivity in
LaFeAsO disappears by 3% Zn substitution, we found that NMR/NQR
spectra and NMR physical quantities in the normal state are hardly changed,
indicating that the crystal structure and electronic states are not modified by
Zn substitution. Our results suggest that the suppression of superconductivity
by Zn substitution is not due to the change of the normal-state properties, but
due to strong non-magnetic pair-breaking effect to superconductivity.Comment: 5 pages, 4 figures, This paper was chosen as "Paper of Editors'
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Orbital Properties of Sr3Ru2O7 and Related Ruthenates Probed by 17O-NMR
We report a site-separated O-NMR study of the layered perovskite
ruthenate SrRuO, which exhibits nearly two-dimensional transport
properties and itinerant metamagnetism at low temperatures. The local hole
occupancies and the spin densities in the oxygen orbitals are obtained by
means of tight-binding analyses of electric field gradients and anisotropic
Knight shifts. These quantities are compared with two other layered perovskite
ruthenates: the two-dimensional paramagnet SrRuO and the
three-dimensional ferromagnet SrRuO. The hole occupancies at the oxygen
sites are very large, about one hole per ruthenium atom. This is due to the
strong covalent character of the Ru-O bonding in this compound. The magnitude
of the hole occupancy might be related to the rotation or tilt of the RuO
octahedra. The spin densities at the oxygen sites are also large, 20-40% of the
bulk susceptibilities, but in contrast to the hole occupancies, the spin
densities strongly depend on the dimensionality. This result suggests that the
density-of-states at the oxygen sites plays an essential role for the
understanding of the complex magnetism found in the layered perovskite
ruthenates.Comment: 9 pages, 5 figures, to be published in Phys. Rev.
Mineralogia de argilas em cambissolos do Sudoeste da Amazônia brasileira.
bitstream/item/40418/1/Boletim-Pesquisa-34-CPATU.pd
Unconventional superconductivity and antiferromagnetic quantum critical behavior in the isovalent-doped BaFe2(As1-xPx)2
Spin dynamics evolution of BaFe(AsP) was probed as a
function of P concentration via P NMR. Our NMR study reveals that
two-dimensional antiferromagnetic (AF) fluctuations are notably enhanced with
little change in static susceptibility on approaching the AF phase from the
superconducting dome. Moreover, magnetically ordered temperature
deduced from the relaxation rate vanishes at optimal doping. These results
provide clear-cut evidence for a quantum-critical point (QCP), suggesting that
the AF fluctuations associated with the QCP play a central role in the
high- superconductivity.Comment: 5 pages, 3 figure
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