Breathing pyrochlore magnet CuGaCr4S8 : Magnetic, thermodynamic, and dielectric properties

We investigate the crystallographic and magnetic properties of a chromium-based thiospinel ${\mathrm{CuGaCr}}_{4}{\mathrm{S}}_{8}$. From a synchrotron x-ray diffraction experiment and structural refinement, Cu and Ga atoms are found to occupy the tetrahedral A sites in an alternate way, yielding breathing pyrochlore Cr network. ${\mathrm{CuGaCr}}_{4}{\mathrm{S}}_{8}$ undergoes a magnetic transition associated with a structural distortion at 31 K in zero magnetic field, indicating that the spin-lattice coupling is responsible for relieving the geometrical frustration. When applying a pulsed high magnetic field, a sharp metamagnetic transition takes place at 40 T, followed by a 1/2-magnetization plateau up to 103 T. These phase transitions accompany dielectric anomalies, suggesting the presence of helical spin correlations in low-field phases. The density functional theory calculations suggest that ${\mathrm{CuGaCr}}_{4}{\mathrm{S}}_{8}$ is dominated by antiferromagnetic and ferromagnetic exchange couplings within small and large tetrahedra, respectively, in analogy with ${\mathrm{CuInCr}}_{4}{\mathrm{S}}_{8}$. We argue that A-site-ordered Cr thiospinels serve as an excellent platform to explore diverse magnetic phases along with pronounced magnetoelastic and magnetodielectric responses.