Theoretical Investigation of the Magnetic Order in FeAs
  The magnetic structure of the iron monoarsenide FeAs is studied using first-principles calculations. We consider the collinear and non-collinear (spin-spiral wave) magnetic ordering and magnetic anisotropy. It is analitically shown that a magnetic triaxial anisotropy results in a sum of two spin-spiral waves with opposite directions of wave vectors and different spin amplitudes, so that the magnetic moments in two perpendicular directions do not equal each other. 
Dobysheva Lyudmila V. and Arzhnikov Anatoly K
cond-mat.mtrl-sci