Non-collinear antiferromagnetism in FeCrAs Special issue on Neutron Scattering in Canada.

FeCrAs undergoes a magnetic ordering transition at TN ≃ 125 K. The magnetic structure of FeCrAs, which crystallizes in space group [Formula: see text] and is isostructural to Fe2P, was determined by constant wavelength neutron powder diffraction. A single basis function was found to describe the intensity distribution in the magnetic satellite reflections, which are associated with propagation vector k = (1/3, 1/3, 0), representing a K-point zone-boundary ordering. The magnetic intensity could be modelled by moments from Cr only, which lie on the 3g-sites, in pyramidal coordination by As, whereas the moments on Fe, in tetrahedral coordination on the 3f-sites, were found to be so small as to be zero within error. This agrees with previous Mössbauer spectroscopy measurements on this compound. The magnetic structure is characterized by non-collinear antiferromagnetic order of the moments, all of which lie in the hexagonal plane. This does not appear to have been observed in other monopnictides with Fe2P structure but is consistent with geometric frustration of antiferromagnetic interactions.