Neutron Diffraction Study of Successive Magnetic Phase Transitions of Distorted-Triangular-Lattice Antiferromagnet RbFeBr3

The successive magnetic phase transitions of the distorted-triangular-lattice antiferromagnet RbFeBr 3 have been investigated by single-crystal neutron diffraction measurements. The intermediate magnetic phase ( T N2 = 2.0 K< T < T N1 = 5.6 K) appears as a partially disordered (PD) spin structure. An inclusive understanding of a distortion model of this crystal with the symmetry P 6 3 c m , which enables the spontaneous electric polarization and the PD spin structure with a weak ferromagnetic moment, was established.