Incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs studied by inelastic neutron scattering

TL;DR

This study investigates incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs using inelastic neutron scattering, revealing their energy range, magnetic origin, and weak anisotropy, with implications for understanding magnetic interactions in this superconductor.

Contribution

It provides the first detailed characterization of incommensurate magnetic fluctuations in LiFeAs, including their energy dependence, magnetic nature, and anisotropy, using advanced neutron scattering techniques.

Findings

Magnetic fluctuations persist up to 60 meV energy transfer.

Fluctuations are eight times weaker than in Co-doped BaFe2As2.

Weak spin space anisotropy with slightly stronger out-of-plane component.

Abstract

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.