Broken C_{4} symmetry in the tetragonal state of uniaxial strained BaCo_{0.9}Ni_{0.1}S_{1.9}

Abstract

A compound with large anions is known to show large compressibility, whereby a novel response may emerge from the degenerated state by a uniaxial pressure. Neutron scattering study of BaCo_{0.9}Ni_{0.1}S_{1.9} crystal reveals that the tetragonal insulating state has two magnetic domains with in-plane anisotropic antiferromagnetic wave vectors Q_{1}=(π,0) and Q_{2}=(0,π). The magnetic order with in-plane broken C_{4} symmetry is realized as a twin of these two domains in the tetragonal state without any strain. One magnetic domain with Q_{2} becomes dominant under a weak strain without any appreciable structural distortion. Correspondingly, the in-plane broken C_{4} symmetry is also observed in the in-plane magnetic excitation of the tetragonal state.