4f²配位系PrIr₂Zn₂₀における反強多極子秩序

抄録

A cubic 4f² system PrIr₂Zn₂₀ exhibits a superconducting transition at 0.05 K below a quadrupolar transition at 0.11 K. We have conducted neutron diffraction measurements in magnetic fields B ≤ 5 T down to 0.04 K to determine the order parameter expected for the non-Kramers ground state doublet. Field-induced magnetic reflection appears at Q = (1/2, 1/2, –3/2) together with some of its equivalents in B || [1 −1 0]. Thus, the antiferroquadrupole order is characterized by the propagation vector q = (1/2, 1/2, 1/2). The magnetic-structure-factor analysis revealed that the magnetic moments are induced along the [1 1 1] axis on the Pr-ion diamond sublattice. In contrast, no reflections appear for B || [0 0 1] as well as in zero field. The results indicate that the O₂²-type quadrupole is the primary order parameter which entangles with other various multipolar degrees of freedom. Such entanglements should play the role in the enriched B-T phase diagram of PrIr₂Zn₂₀ including the non-Fermi liquid state and field-induced Fermi liquid state.