We present a comprehensive neutron scattering study of the breathing pyrochlore magnet LiGaCr4S8. We observe an unconventional magnetic excitation spectrum with a separation of high and low-energy spin dynamics in the correlated paramagnetic regime above a spin-freezing transition at 12(2) K. By fitting to magnetic diffuse-scattering data, we parameterize the spin Hamiltonian. We find that interactions are ferromagnetic within the large and small tetrahedra of the breathing pyrochlore lattice, but antiferromagnetic further-neighbor interactions are also essential to explain our data, in qualitative agreement with density-functional theory predictions [Ghoshet al.,npj Quantum Mater.4, 63 (2019)]. We explain the origin of geometrical frustration in LiGaCr4S8 interms of net antiferromagnetic coupling between emergent tetrahedral spin clusters that occupy a face-centered lattice. Our results provide insight into the emergence of frustration in the presence of strong further-neighbor couplings, and a blueprint for the determination of magnetic interactions in classical spin liquids.
@article{arxiv.2002.09749,
title = {Cluster Frustration in the Breathing Pyrochlore Magnet LiGaCr4S8},
author = {Ganesh Pokharel and Hasitha Suriya Arachchige and Travis J. Williams and Andrew F. May and Randy S. Fishman and Gabriele Sala and Stuart Calder and Georg Ehlers and David S. Parker and Tao Hong and Andrew Wildes and David Mandrus and Joseph A. M. Paddison and Andrew D. Christianson},
journal= {arXiv preprint arXiv:2002.09749},
year = {2020}
}