Large diamagnetism and low-lying optical phonon modes in Pt–Cd γ-phase

Abstract

Multi-shell polyhedral clusters appear as building blocks in the crystal structures of quasicrystals and cage compounds. The multi-shell clusters in these materials are expected to provide characteristic features in the thermal, electronic, and magnetic properties, which still remain to be clarified. To shed light on this issue, we studied the electrical transport, heat capacity, and magnetic properties of Pt0.19Cd0.81 single crystals. Specific heat measurements and ab initio calculations of phonon modes revealed that the optical modes consist of extremely low-energy T2 triplet branches at as low as ~30 K and a highly dense continuum above ~50 K. The latter can account for a crossover behavior in the temperature dependence of the electrical resistivity. In the magnetic susceptibility, an anomalously large diamagnetic contribution attributable to the electrons’ orbital motion was observed. Possible origins, including the flow of ring currents in the multi-shell clusters and interband effects near possible Dirac points, are discussed.