Low-temperature instabilities in the multiorbital magnet CuCr2Se4

Competing valence distributions across the interpenetrating sublattices of spinel materials have long been subject to debate. While many such compounds, like CuCr2Se4, 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 the sister compound CuCr2S4 is associated with the formation of a commensurate superstructure. However, it remains unclear which magnetic structure (conical or spin density wave) describes the observed superstructure. 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 neutron single crystal diffraction, we propose to track the evolution of the magnetic structure of a CuCr2Se4 crystal.