Non-collinear spin-density wave antiferromagnetism in FeAs

TL;DR

This paper investigates the magnetic structure of FeAs, revealing a non-collinear spin-density wave with incommensurate modulation, temperature-dependent propagation vector, and mixed itinerant-localized magnetic behavior, advancing understanding of magnetism in iron arsenides.

Contribution

It provides the first detailed characterization of FeAs's magnetic structure as a non-collinear spin-density wave, highlighting the interplay between itinerant and localized magnetism.

Findings

Incommensurate wavevector q = (0.395±0.001)c* at 4 K

Spin amplitude along b-axis is 15±5% larger than along a-axis

Magnetic propagation vector varies with temperature

Abstract

We present the magnetic structure of the itinerant monoarsenide, FeAs, with the B31 structure. Powder neutron diffraction confirms incommensurate modulated magnetism with wavevector $\mathbf{q} = (0.395\pm0.001)\mathbf{c}^*$ at 4 K, but cannot distinguish between a simple spiral and a collinear spin-density wave structure. Polarized single crystal diffraction confirms that the structure is best described as a non-collinear spin-density wave arising from a combination of itinerant and localized behavior with spin amplitude along the b-axis direction being (15 $\pm$ 5)% larger than in the a-direction. Furthermore, the propagation vector is temperature dependence, and the magnetization near the critical point indicates a two-dimensional Heisenberg system. The nature of the magnetism in the simplest iron arsenide is of fundamental importance in understanding the interplay between localized and itinerant magnetism and superconductivity.