Investigation of the oxohalogenide Cu4Te5O12Cl4 with weakly coupled Cu(II) tetrahedra

TL;DR

This study investigates the crystal structure and magnetic properties of Cu4Te5O12Cl4, revealing weakly coupled Cu tetrahedra, antiferromagnetic frustration, and a magnetic transition at 13.6 K, with insights into exchange interactions and quantum fluctuations.

Contribution

The paper provides detailed structural and magnetic characterization of Cu4Te5O12Cl4, highlighting differences from similar compounds and elucidating exchange pathways and magnetic excitations.

Findings

Weakly coupled Cu tetrahedra structure identified

Antiferromagnetic long-range order at 13.6 K observed

Magnetic excitation at approximately 50 K energy scale detected

Abstract

The crystal structure of the copper(II) tellurium(IV) oxochloride Cu$_{4}$Te$_{5}$O$_{12}$Cl$_{4}$ (Cu-45124) is composed of weakly coupled tetrahedral Cu clusters and shows crystallographic similarities with the intensively investigated compound Cu$_{2}$Te$_{2}$O$_{5}$X$_{2}$, with X~=~Cl, Br (Cu-2252). It differs from the latter by a larger separation of the tetrahedra within the crystallographic ab plane, that allows a more direct assignment of important inter-tetrahedra exchange paths and the existence of an inversion center. Magnetic susceptibility and specific heat evidence antiferromagnetic, frustrated correlations of the Cu spin moments and long range ordering with $T_{c}$=13.6 K. The entropy related to the transition is reduced due to quantum fluctuations. In Raman scattering a well structured low energy magnetic excitation is observed at energies of $\approx$50K (35cm$^{-1})$. This energy scale is reduced as compared to Cu-2252.