Magnetization plateaux of the S = 1/2 two-dimensional frustrated antiferromagnet Cs2CuBr4

The field induced magnetic phase transitions of Cs2CuBr4 were investigated by means of a magnetization process and neutron scattering experiments. This system undergoes a magnetic phase transition at N?el temperature TN = 1.4?K at zero field, and exhibits a magnetization plateau at approximately one third of the saturation magnetization for the field directions and . In the present study, an additional symptom of the two-third magnetization plateau was found in the field derivative of the magnetization process. The magnetic structure was found to be incommensurate with the ordering vector Q = (0,0.575,0) at zero field. With increasing magnetic field parallel to the c-axis, the ordering vector increases continuously and is locked at Q = (0,0.662,0) in the plateau field range 13.1?T< H<14.4?T. This indicates that the collinear up?up?down spin structure is stabilized by quantum fluctuation at the magnetization plateau.