Geometrical Quadrupolar Frustration in DyB₄

Abstract

Physical properties of DyB₄ have been studied by magnetization, specific heat, and ultrasonic measurements. The magnetic entropy change and ultrasonic properties in intermediate phase II 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 C₄₄ in phase II suggest the existence of electric-quadrupolar (orbital) fluctuations of 4f-electrons. These unusual properties originate from a geometrical quadrupolar frustration.