Phase diagram and spin Hamiltonian of weakly-coupled anisotropic S=1/2 chains in CuCl2*2((CD3)2SO)

TL;DR

This study investigates the magnetic phase diagram of CuCl2*2((CD3)2SO), revealing how external magnetic fields influence magnetic order, energy gaps, and phase transitions due to anisotropic interactions and staggered fields.

Contribution

It provides the first detailed phase diagram and analysis of the spin Hamiltonian for weakly-coupled anisotropic S=1/2 chains in this compound, highlighting the effects of field direction and strength.

Findings

Magnetic order appears below 0.93K with a moment of 0.44μB.

Fields along different axes either strengthen or suppress magnetic order, inducing energy gaps.

Critical exponents match 3D Heisenberg behavior for thermal transitions, but differ for quantum-driven transitions.

Abstract

Field-dependent specific heat and neutron scattering measurements were used to explore the antiferromagnetic S=1/2 chain compound CuCl2 * 2((CD3)2SO). At zero field the system acquires magnetic long-range order below TN=0.93K with an ordered moment of 0.44muB. An external field along the b-axis strengthens the zero-field magnetic order, while fields along the a- and c-axes lead to a collapse of the exchange stabilized order at mu0 Hc=6T and mu0 Hc=3.5T, respectively (for T=0.65K) and the formation of an energy gap in the excitation spectrum. We relate the field-induced gap to the presence of a staggered g-tensor and Dzyaloshinskii-Moriya interactions, which lead to effective staggered fields for magnetic fields applied along the a- and c-axes. Competition between anisotropy, inter-chain interactions and staggered fields leads to a succession of three phases as a function of field applied along the c-axis. For fields greater than mu0 Hc, we find a magnetic structure that reflects the symmetry of the staggered fields. The critical exponent, beta, of the temperature driven phase transitions are indistinguishable from those of the three-dimensional Heisenberg magnet, while measurements for transitions driven by quantum fluctuations produce larger values of beta.