Analysis by Representation Theory of Helical Spin Structures. Application to Dy and MnP

Abstract

We have extended representation analysis of magnetic structures to arbitrary wave vectors k by defining ``k components of spins'' which transform like Bloch waves. The theory provides all possible isotropic and anisotropic couplings which are compatible with k. Applied to the helical structure of Dy the theory shows that antisymmetric coupling cannot be ruled out. For MnP the possible presence of antisymmetric coupling provides an explanation which is different from that recently forwarded by Takeuchi and Motizuki.