Dipolar-glass model for lead magnesium niobate

The static polarization of lead magnesium niobate has been studied using a standard Sawyer-Tower circuit. The square-to-slim-loop hysteresis transition was phenomenologically modeled by modifying N\'eel's equation for the magnetization of a superparamagnet to a similar relationship for a superparaelectric. A temperature-dependent internal dipole field was included to account for cluster interactions. The slim-loop polarization curves were found to scale to E/(T-Tf), where E is the electric field and Tf the freezing temperature. A glassy character was subsequently proposed to exist in the zero-field-cooled state with local dipole fields between superparaelectric moments controlling the kinetics of the polarization reversals and the freezing process. Recent quasielastic-neutron-scattering results have been interpreted to support this model.