Local symmetry lowering in the cubic intermetallics YbPdBi and YbNiSb

Abstract

A microscopic investigation of the cubic ternary alloys YbPdBi and YbNiSb, using 170Yb Mossbauer spectroscopy, reveals that the point symmetry at the site of the Yb3+ is far from cubic in both compounds. An analysis of the thermal variation of the quadrupolar 4f moment shows that the energy of the first crystal electric field transition is close to 20 K in YbPdBi and to 10 K in YbNiSb. Specific heat measurements are also presented in YbPdBi, and magnetic ordering is detected below 1 K in YbPdBi, with saturated Yb3+ moments of 1.25 mu B, and below 0.85 K in YbNiSb, with saturated moments of 1 mu B. A tentative explanation of the Yb site symmetry breaking is made in terms of a Jahn-Teller distortion within the Gamma 8 cubic quartet.