Ground state order and spin-lattice coupling in tetrahedral spin systems Cu2Te2O5X2

TL;DR

This study investigates the magnetic and thermal properties of Cu2Te2O5X2 (X=Br,Cl) single crystals, revealing strong spin-lattice coupling and complex magnetic states in the Cl variant, with less definitive behavior in the Br variant.

Contribution

It provides detailed experimental insights into the spin-lattice interactions and magnetic ground states of Cu2Te2O5X2, highlighting the differences between Br and Cl samples.

Findings

Cl-sample exhibits a transition at 18.5 K with complex magnetic behavior.

Strong spin-lattice coupling observed in Cl-sample, not in Br-sample.

Cl-sample shows signs of antiferromagnetic order and a possible excitation gap.

Abstract

High-resolution ac susceptibility and thermal conductivity measurement on Cu2Te2O5X2(X=Br,Cl) single crystals are reported. For Br-sample, sample dependence prevents to distinguish between possibilities of magnetically ordered and spin-singlet ground states. In Cl-sample a three-dimensional transition at 18.5 K is accompanied by almost isotropic behavior of susceptibility and almost switching behavior of thermal conductivity. Thermal conductivity studies suggest the presence of a tremendous spin-lattice coupling characterizing Cl- but not Br-sample. Below the transition Cl-sample is in a complex magnetic state involving AF order but also the elements consistent with the presence of a gap in the excitation spectrum.