We present the magnetic structure of the itinerant monoarsenide, FeAs, with the B31 structure. Powder neutron diffraction confirms incommensurate modulated magnetism with wavevector q=(0.395±0.001)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 ± 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.
@article{arxiv.1012.5311,
title = {Non-collinear spin-density wave antiferromagnetism in FeAs},
author = {E. E. Rodriguez and C. Stock and K. Krycka and C. F. Majkrzak and K. Kirshenbaum and N. P. Butch and S. R. Shanta and J. Paglione and M. A. Green},
journal= {arXiv preprint arXiv:1012.5311},
year = {2011}
}