Wang, Z.; Kamenskyi, D.; Cepas, O.; Schmidt, M.; Quintero-Castro, D.L.; Islam, A.T.M.N.; Lake, B.; Aczel, A.A.; Dabkowska, H.A.; Dabkowski, A.B.; Luke, G.M.; Wan, Y.; Loidl, A.; Ozerov, M.; Wosnitza, J.; Zvyagin, S.A.; Deisenhofer, J.: High-field electron spin resonance spectroscopy of singlet-triplet transitions in the spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8. Physical Review B 89 (2014), p. 174406/1-6
10.1103/PhysRevB.89.174406

Abstract:
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.