Crossover from impurity-induced ordered phase to uniform antiferromagnetic phase under hydrostatic pressure in the doped spin-gap system TlCu$_{1-x}$Mg$_x$Cl$_3$

TL;DR

This study investigates how hydrostatic pressure induces a transition from impurity-induced magnetic order to a uniform antiferromagnetic phase in a doped spin-gap system, revealing a crossover at approximately 1.3 kbar.

Contribution

It demonstrates the pressure-driven crossover from impurity-induced order to a uniform antiferromagnetic phase in TlCu$_{1-x}$Mg$_x$Cl$_3$, highlighting the role of gap shrinkage and exchange interactions.

Findings

Impurity-induced magnetic ordering at ambient pressure with $T_N=2.5$ K.

Increase in $T_N$ with pressure due to enhanced exchange interactions.

Transition to a uniform antiferromagnetic phase at around 1.3 kbar.

Abstract

Magnetic phase transition under hydrostatic pressure in TlCu$_{0.988}$Mg$_{0.012}$Cl$_3$ was investigated by magnetization measurements. The parent compound TlCuCl$_3$ is a coupled spin dimer system, which undergoes a pressure-induced quantum phase transition from a gapped ground state to an antiferromagnetic state at $P_{\rm c} = 0.42$ kbar due to the shrinkage of the gap. At ambient pressure, the present doped system exhibits impurity-induced magnetic ordering at $T_{\rm N}=2.5$ K. With increasing pressure, $T_{\rm N}$ increases. This is because the effective exchange interaction $J_{\rm eff}$ between unpaired spins is enhanced by the shrinkage of the gap. With a further increase in pressure, the present system undergoes a phase transition to a uniform antiferromagnetic phase due to the closing of the triplet gap in the intact dimers. The crossover from the impurity-induced ordered phase to the uniform antiferromagnetic phase occurs at $P \simeq 1.3$ kbar.