Superstructures of the multiorbital magnet CuCr2S4

Competing valence distributions across the interpenetrating sublattices of thiospinel materials have long been subject to debate. While many such compounds, like CuCr2S4, are simple (room temperature) ferromagnets, we were recently able to observe multiple low-temperature transitions by local magnetic probes. Moreover, using neutron powder diffraction, we discovered that at least one of the transitions in CuCr2S4 is associated with the formation of a commensurate superstructure. However, it remains unclear whether this should be assigned fully to structural or magnetic degrees of freedom, or to both. To understand the mechanisms of these transitions, we need to clarify whether (and how) they arise from the frustration of charge/valence and magnetic degrees of freedom on the spinel lattice. Using low-temperature high-resolution X-ray powder diffraction, we propose to track the evolution of the structure, quantify magnetoelastic coupling and determine the origin of the superstructure.