Synthesis, physical and magnetic properties of CuAlCr$_4$S$_8$: a new Cr-based breathing pyrochlore

TL;DR

This study synthesizes and characterizes a new CuAlCr4S8 breathing pyrochlore, revealing its magnetic transition at 20 K, positive thermal expansion, and the influence of pressure on its magnetic properties, highlighting the role of the breathing factor.

Contribution

It introduces a new Cr-based breathing pyrochlore with detailed physical and magnetic property analysis, emphasizing the tunability of magnetic ground states via the breathing ratio.

Findings

Sharp antiferromagnetic transition at 20 K

Pressure shifts the magnetic transition by up to 3.2 K

Breathing ratio of 1.0663(8) comparable to other sulfur pyrochlores

Abstract

We present the synthesis and physical properties of a new breathing pyrochlore magnet CuAlCr$_4$S$_8$ with the help of synchrotron x-ray diffraction (XRD), magnetization under ambient and applied hydrostatic pressure, heat capacity, and muon spin relaxation/rotation ($\mu$SR) measurements. CuAlCr$_4$S$_8$ exhibits positive thermal expansion with concave upward temperature dependence. We observed a sharp antiferromagnetic ordering transition of a purely magnetic nature at 20 K, which shifts by as much as 3.2 K on the application of 600 MPa pressure. The breathing factor (B$_f$ = $J'/J$) in breathing pyrochlores can be an important parameter to tune the magnetic ground states of the pyrochlore lattice. The breathing factor can be modulated through breathing ratio, the ratio of sizes of the two tetrahedra, by using different elements at A and A' sites in the breathing pyrochlore structure. We find that CuAlCr$_4$S$_8$ has a breathing ratio of 1.0663(8), which is comparable to other sulfur breathing pyrochlores.