Magnetism of C₆Eu. II. Instability of the Triangular Spin Structure in the hcp-Like Antiferromagnet

Abstract

Possible spin structures of the hcp-like triangular antiferromagnet are examined and the phase diagram is given. It is found that the well known triangular spin structure is unstable against an infinitesimal inter-layer exchange coupling, and two kinds of incommensurate structures appear according to the sign of the intra-layer next nearest neighbor exchange interaction.