Non-collinear antiferromagnetism in FeCrAs special issue on neutron scattering in Canada

FeCrAs undergoes a magnetic ordering transition at T_N 125 K. The magnetic structure of FeCrAs, which crystallizes in space group P6̄2m 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 Mssbauer 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.