Complex magnetostructural order in the frustrated spinel LiInCr4O8.

We present a neutron scattering study of the chromate spinel LiInCr4O8, which realizes a "breathing" pyrochlore lattice of S = 3/2 spins. High-resolution neutron diffraction reveals a phase separation into a mixture of minority cubic and majority tetragonal phases below 18 K, followed by apparent magnetic order in a complex two-up two-down pattern in the latter around 12 K. The spin-spin correlation length appears to remain small down to 1.7 K. Above both transitions, time-of-flight neutron spectroscopy shows that the response is inelastic rather than quasielastic, consistent with the relatively large alternation in sizes of adjacent Cr tetrahedra. Finally, a remarkable softening of the inelastic mode is observed preceding the structural transition, implying proximity to a critical point. [ABSTRACT FROM AUTHOR]