Geometrical quadrupolar frustration in DyB$_4$

TL;DR

This paper investigates DyB4, revealing that geometrical quadrupolar frustration leads to persistent internal degeneracy and orbital fluctuations, despite magnetic ordering, as evidenced by magnetization, heat, and ultrasonic measurements.

Contribution

It uncovers the role of geometrical quadrupolar frustration in DyB4, highlighting its impact on magnetic and orbital properties in the intermediate phase.

Findings

Degeneracy remains in phase II despite magnetic order

Ultrasonic attenuation indicates electric-quadrupolar fluctuations

Significant softening of elastic constant C44 observed in phase II

Abstract

Physical properties of DyB$_4$ have been studied by magnetization, specific heat, and ultrasonic measurements. The magnetic entropy change and the ultrasonic properties in the 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 the huge softening of $C_{44}$ in phase II suggests existence of electric-quadrupolar (orbital) fluctuations of the 4$f$-electron. These unusual properties originate from the geometrical quadrupolar frustration.