Low-temperature ordered phases of the spin-$\frac{1}{2}$ XXZ chain system Cs$_2$CoCl$_4$

TL;DR

This paper investigates the low-temperature magnetic phases of the spin-1/2 XXZ chain system Cs$_2$CoCl$_4$ using high-resolution thermal expansion and specific heat measurements, revealing complex phase transitions under varying magnetic fields.

Contribution

It provides the first detailed experimental phase diagram of Cs$_2$CoCl$_4$ under different magnetic field orientations and identifies multiple phase transitions including a two-stage spin-flop transition.

Findings

Magnetic order is suppressed at about 2.1 T for fields along a or c.

An intermediate phase appears before saturation near 2.5 T.

Two additional transitions at 0.25 T and 0.7 T suggest a two-stage spin-flop transition.

Abstract

In this study the magnetic order of the spin-1/2 XXZ chain system Cs$_2$CoCl$_4$ in a temperature range from 50 mK to 0.5 K and in applied magnetic fields up to 3.5 T is investigated by high-resolution measurements of the thermal expansion and the specific heat. Applying magnetic fields along a or c suppresses $T_\textrm{N}$ completely at about 2.1 T. In addition, we find an adjacent intermediate phase before the magnetization saturates close to 2.5 T. For magnetic fields applied along b, a surprisingly rich phase diagram arises. Two additional transitions are observed at critical fields $\mu_0 H_{SF1}\simeq 0.25$ T and $\mu_0 H_{SF2}\simeq 0.7$ T, which we propose to arise from a two-stage spin-flop transition.