Multiple lattice instabilities resolved by magnetic-field and disorder   sensitivities in cubic paramagnetic phase of the orbital-degenerate   frustrated spinel MgV$_2$O$_4$
  Ultrasound velocity measurements of the orbital-degenerate frustrated spinel MgV$_2$O$_4$ are performed in the 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, and concave temperature dependence with a characteristic minimum. These elastic anomalies suggest the coupling of lattice to coexisting orbital fluctuations and orbital-spin-coupled excitations. 
Tadataka Watanabe, Takashi Ishikawa, Shigeo Hara, A. T. M. Nazmul   Islam, Elisa M. Wheeler and Bella Lake
cond-mat.str-el cond-mat.mtrl-sci