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

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.

9 pages, 5 figures, jpsj2 class file, to be published in J. Phy. Soc. Jpn. Vol.75 No.3 (2006); layout changed, unrelated figure removed