Coexistence of the critical slowing down and glassy freezing in relaxor ferroelectrics

We have developed a dynamical model for the dielectric response in relaxor ferroelectrics that explicitly takes into account the coexistence of the critical slowing down and glassy freezing. The application of the model to the experiment in PbMg1/3Nb2/3O3 (PMN) allowed for the reconstruction of the nonequilibrium spin-glass state order parameter and its comparison with the results of recent NMR experiment [R. Blinc er al., Phys. Rev. Lett 83, 424 (1999)]. It is shown that the degree of the local freezing is rather small even at temperatures where the held-cooled permittivity exceeds the frequency-dependent permittivity by an order of magnitude. This observation indicates the significant role of the critical slowing down (accompanying the glass freezing) in the system dynamics. Also, the theory predicts an important interrelationship between the frequency-dependent permittivity and the zero-field-cooled permittivity, which proved to be consistent with the experiment in PMN.