Incommensurate antiferromagnetic fluctuations in single-crystalline   LiFeAs studied by inelastic neutron scattering
  We present an inelastic neutron scattering study on single-crystalline LiFeAs devoted to the characterization of the incommensurate antiferromagnetic fluctuations at $\mathbf{Q}=(0.5\pm\delta, 0.5\mp\delta, q_l)$. Time-of-flight measurements show the presence of these magnetic fluctuations up to an energy transfer of 60 meV, while polarized neutrons in combination with longitudinal polarization analysis on a triple-axis spectrometer prove the pure magnetic origin of this signal. The normalization of the magnetic scattering to an absolute scale yields that magnetic fluctuations in LiFeAs are by a factor eight weaker than the resonance signal in nearly optimally Co-doped BaFe$_2$As$_2$, although a factor two is recovered due to the split peaks owing to the incommensurability. The longitudinal polarization analysis indicates weak spin space anisotropy with slightly stronger out-of-plane component between 6 and 12 meV. Furthermore, our data suggest a fine structure of the magnetic signal most likely arising from superposing nesting vectors. 
N. Qureshi, P. Steffens, D. Lamago, Y. Sidis, O. Sobolev, R. A.   Ewings, L. Harnagea, S. Wurmehl, B. B\"uchner and M. Braden
cond-mat.supr-con