Drastic Change of Magnetic Phase Diagram in Doped Quantum Antiferromagnet TlCu$_{1-x}$Mg$_x$Cl$_3$

TL;DR

This study investigates how doping TlCuCl₃ with Mg alters its magnetic phase diagram, revealing that impurity- and field-induced magnetic orders become indistinguishable and the original gapped spin liquid state is eliminated.

Contribution

It provides experimental evidence that doping with Mg destroys the gapped spin liquid state and causes impurity- and field-induced magnetic orders to merge in TlCuCl₃.

Findings

Impurity- and field-induced magnetic phases are identical in doped TlCuCl₃.

The original gapped spin liquid state is eliminated by minimal doping.

Doping causes a drastic change in the magnetic phase diagram.

Abstract

TlCuCl$_3$ is a coupled spin dimer system, which has a singlet ground state with an excitation gap of $\Delta/g\mu_{\mathrm B}$ = 5.5 T. TlCu$_{1-x}$Mg$_x$Cl$_3$ doped with nonmagnetic Mg$^{2+}$ ions undergoes impurity-induced magnetic ordering. Because triplet excitation with a finite gap still remains, this doped system can also undergo magnetic-field-induced magnetic ordering. By specific heat measurements and neutron scattering experiments under a magnetic field, we investigated the phase diagram in TlCu$_{1-x}$Mg$_x$Cl$_3$ with $x\sim 0.01$, and found that impurity- and field-induced ordered phases are the same. The gapped spin liquid state observed in pure TlCuCl$_3$ is completely wiped out by the small amount of doping.