Ultrasound velocity measurements in orbital degenerate frustrated spinel MgV2O4

Ultrasound velocity measurements of the orbital degenerate frustrated spinel MgV2O4 are performed in the disorder free 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 coexisting two types of anomalous temperature dependence of the elastic moduli in the cubic paramagnetic phase Curie type softening with decreasing temperature, and softening with a characteristic minimum with decreasing temperature. These elastic anomalies should respectively originate from the coexisting orbital fluctuations and spin cluster excitation