Possible spin singlet quadrumerization in Pb(2)Re(2)O(7-δ).

Abstract

A single crystal of pyrochlore Pb(2)Re(2)O(6.75) was prepared by hydrothermal synthesis, and its magnetic and transport properties were investigated. Pb(2)Re(2)O(6.75) shows the metallic conduction with an anomalous second-order structural phase transition at T(s)=294 K, in which the magnetization and the structure change similarly to that at 200 K of the superconductor Cd(2)Re(2)O(7). A three-dimensional Ising-like order parameter probed by the atomic displacement suggests that an unconventional spin singlet state is possibly realized in the ground state of Pb(2)Re(2)O(6.75), in which four spins make a quadrumer in order to remove the spin frustration of the pyrochlore lattice.