In-plane spin excitation anisotropy in the paramagnetic state of NaFeAs

Yu Song, Louis Pierre Regnault, Chenglin Zhang, Guotai Tan, Scott V. Carr, Songxue Chi, A. D. Christianson, Tao Xiang, Pengcheng Dai

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    35 Scopus citations

    Abstract

    We use unpolarized and polarized inelastic neutron scattering to study low-energy spin excitations in NaFeAs, which exhibits a tetragonal-to- orthorhombic lattice distortion at Ts≈58 K followed by a collinear antiferromagnetic (AF) order below TN≈45 K. In the AF ordered state (T<TN), spin waves are entirely c-axis polarized below ∼10 meV, exhibiting a gap of ∼4 meV at the AF zone center and disperse to ∼7 meV near the c-axis AF zone boundary. On warming to the paramagnetic state with orthorhombic lattice distortion (TN<T<T s), spin excitations become anisotropic within the FeAs plane. Upon further warming to the paramagnetic tetragonal state (T>Ts), spin excitations become more isotropic. Since similar magnetic anisotropy is also observed in the paramagnetic tetragonal phase of superconducting BaFe 1.904Ni0.096As2, our results suggest that the spin excitation anisotropy in superconducting iron pnictides originates from similar anisotropy already present in their parent compounds.

    Original languageEnglish
    Article number134512
    JournalPhysical Review B - Condensed Matter and Materials Physics
    Volume88
    Issue number13
    DOIs
    StatePublished - Oct 17 2013

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