A Single-Crystal Neutron Diffraction Study on Magnetic Structure of the Quasi-One-Dimensional Antiferromagnet SrCo_2V_2O_8

The magnetic structure of the spin-chain antiferromagnet SrCo_2V_2O_8 is determined by single-crystal neutron diffraction experiment. The system undergoes a long-range magnetic order below the critical temperature T_\rm N=4.96 K. The moment of 2.16 \mu__\rm B per Co at 1.6 K in the screw chain running along the c axis alternates in the c axis. The moments of neighboring screw chains are arranged antiferromagnetically along one in-plane axis and ferromagnetically along the other in-plane axis. This magnetic configuration breaks the four-fold symmetry of the tetragonal crystal structure and leads to two equally populated magnetic twins with the antiferromagnetic vector in the a or b axis. The very similar magnetic state to the isostructural BaCo_2V_2O_8 warrants SrCo_2V_2O_8 as another interesting half-integer spin-chain antiferromagnet for investigation on quantum antiferromagnetism.