Collinear nematic phase in the breathing pyrochlore spinel LiGa0.95In0.05Cr4O8 | LQMEC Synergy

The LiGa1−xInxCr4O8 family has proven to manifest a wide range of magnetic behaviours as a function of the substitution (and hence bond disorder), x. The end member compositions LiGaCr4 O8 (Bf = 0.6) and LiInCr4O8 (Bf = 0.1) exhibit a series of complex magneto-structural transitions resulting in magnetically ordered phases. We have shown that the Néel order is suppressed by even vestigial doping at A′ site; for x = 0.05, magnetic order is replaced with a second-order transition to a possible classical spin nematic phase at Tf ∼ 11 K. Subsequent inelastic neutron scattering experiments reveal a quasi-elastic response at high temperature, as commonly observed in the pyrochlore antiferromagnets. At lower temperatures, this is replaced by an inelastic mode showing a strong resemblance to the broad resonant mode observed in lightly Cd-doped ZnCr2O4. The structure factor of the feature is consistent with “weathervane” modes on hexagonal antiferromagnetic loops, which are abundant in the nematic state. The finite energy of the excitation is proposed to be generated by the biquadratic term in the effective magneto-elastic Hamiltonian, which is also responsible for the onset of the nematic state.