Barkhausen noise in relaxor ferroelectrics

Relaxor ferroelectrics form a diverse class of materials which typically show cooperative freezing into a non-ergodic glassy state without long-range ferroelectric order. We discuss Barkhausen noise techniques in the non-ferroelectric regimes of the relaxors as a probe of the types of glassy order present. Preliminary data on PMN/PT (10% and 32%) show dipole moment step sizes which shrink abruptly upon cooling into the relaxor regime. This is similar to previous results on PMN, but with interesting differences possibly due to the larger ferroelectric correlations in PMN/PT: namely, a history dependence of the noise and a smaller dynamic step size despite larger static ferroelectric correlations. In light of these noise results and aging behavior in PMN/PT and SBN:La, we discuss a tentative new picture we recently proposed of freezing in PMN and related relaxors (analogous to that in reentrant spin glasses) as well as constraints on theoretical models for the relaxors.