Inelastic neutron scattering study of the spin dynamics in the breathing pyrochlore system LiGa_0.95In_0.05Cr₄O₈

The A-site ordered chromate spinels LiGa_1−xIn_xCr₄O₈ host a network of size-alternating spin-3/2 Cr³⁺ tetrahedra known as a 'breathing' pyrochlore lattice. For the x = 0.05 composition, the complex magneto-structural ordering observed in the parent x = 0 material is replaced by a single transition at T_f = 11 K, ascribed to the collinear nematic order caused by strong spin–lattice coupling. We present here an inelastic neutron scattering study of the spin dynamics in this composition. Above T_f, the dynamical scattering function S(Q,E) is ungapped and quasi-elastic, similar to undoped LiGaCr₄O₈. Below T_f, the spectral weight splits between a broad inelastic feature at 5.8 meV and toward the elastic line. The former feature can be ascribed to spin precessions within antiferromagnetic loops, lifted to finite energy by the effective biquadratic spin–lattice term in the spin Hamiltonian. (author)