The Successive Magnetic Phase Transition of Hexagonal Antiferromagnet CsMnI₃Observed by Optical Birefringence

Abstract

Birefringence measurement was made on a triangular lattice antiferromagnet CsMnI 3 at temperatures around the Néel point of 11.42 K. The birefringence for light propagating along the hexagonal c -axis shows that CsMnI 3 has an intermediate ordered phase in the temperature region between 8.20±0.03 K and 11.42 K. Below 8.20 K CsMnI 3 takes the orthorhombic spin structure of the triangular spin arrangement with the spin moments restricted in a plane perpendicular to the basal plane.