Magnetization plateaux of S = 1/2 two-dimensional frustrated antiferromagnet Cs${}_2$CuBr${}_4$

Abstract

The field induced magnetic phase transitions of Cs${}_2$CuBr${}_4$ were investigated by means of magnetization process and neutron scattering experiments. This system undergoes magnetic phase transition at Neél temperature $T_{\mathrm{N}}=1.4$ K at zero field, and exhibits the magnetization plateau at approximately one third of the saturation magnetization for the field directions $H\parallel b$ and $H\parallel c$. In the present study, 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 $\mathbf{Q}=(0,0.575,0)$ at zero field. With increasing magnetic field parallel to the c-axis, the ordering vector increases continuously and is locked at $\mathbf{Q}=(0,0.662,0)$ in the plateau field range $13.1\mathrm{T}<H<14.4\mathrm{T}$. This indicates that the collinear \textit{up-up-down} spin structure is stabilized by quantum fluctuation at the magnetization plateau.

6 pages, 4 Postscript figures, uses iopams.sty and IOPART.CLS