Watanabe, T.; Ishikawa, T.; Hara, S.; Islam, A.T.M.N.; Wheeler, E.M.; Lake, B.: Multiple lattice instabilities resolved by magnetic-field and disorder sensitivities in MgV2O4. Physical Review B 90 (2014), p. 100407/1-6

Ultrasound velocity measurements of the orbitally degenerate frustrated spinel MgV2O4 are performed in a high-purity single crystal which exhibits successive structural and antiferromagnetic phase transitions, and in the disorder-introduced single crystal which exhibits spin-glass-like behavior. The measurements reveal that two types of unusual temperature dependence of the elastic moduli coexist in the cubic paramagnetic phase, which are resolved by magnetic-field and disorder sensitivities: huge Curie-type softening with decreasing temperature (convex temperature dependence), and concave temperature dependence with a characteristic minimum. These elastic anomalies suggest the coupling of the lattice to coexisting orbital fluctuations and spin-cluster excitations.