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

TL;DR

This study investigates the magnetic phase transitions and magnetization plateaux in the frustrated S=1/2 two-dimensional antiferromagnet Cs$_2$CuBr$_4$, revealing a two-third plateau and the stabilization of an up-up-down spin structure due to quantum fluctuations.

Contribution

It provides experimental evidence of a two-third magnetization plateau and details the magnetic structure evolution in Cs$_2$CuBr$_4$, highlighting the role of quantum fluctuations in stabilizing specific spin configurations.

Findings

Discovery of a two-third magnetization plateau.

Incommensurate magnetic structure at zero field.

Locking of the ordering vector in the plateau range.

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 Ne\'{e}l 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 $\boldsymbol{Q}=(0, 0.575, 0)$ at zero field. With increasing magnetic field parallel to the c-axis, the ordering vector increases continuously and is locked at $\boldsymbol{Q}=(0, 0.662, 0)$ 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.