Geometrical quadrupolar frustration in DyB4

Physical properties of DyB4 have been studied by magnetization, specific heat, and ultrasonic measurements. The magnetic entropy change and ultrasonic properties in intermediate phase 11 indicate that the degeneracy of internal degrees of freedom is not fully lifted in spite of the formation of magnetic order. The ultrasonic attenuation and huge softening Of C-44 in phase 11 suggest the existence of electric-quadrupolar (orbital) fluctuations of 4f-electrons. These unusual properties originate from a geometrical quadrupolar frustration.