Regensburg 2007 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 4: Internal Symposium “Order/Disorder versus/with Displacive Behaviour”

DF 4.5: Vortrag

Dienstag, 27. März 2007, 11:40–12:00, H11

Domain states and critical behaviour of random field Ising model systems — •Wolfgang Kleemann — Angewandte Physik, Universität Duisburg-Essen, 47048 Duisburg, Germany

The charge-disordered three-dimensional uniaxial relaxor ferroelectric Sr0.61Ba0.39Nb2O6 splits up into metastable polar nanoregions (PNRs) and paraelectric interfaces upon cooling from above Tc. The frozen PNRs are verified by piezoresponse force microscopy, respond domain-like to dynamic light scattering and dielectric excitation, reveal non-ergodicity at via global aging, and coalesce into polar nanodomains below Tc. Contrastingly, the percolating system of unperturbed interfaces becomes ferroelectric with two-dimensional Ising model-like non-asymptotic critical exponents, , and , as corroborated by ac calorimetry, second harmonic generation, and susceptometry, respectively [1,2]. Signatures of the crossover into the asymptotic critical behavior of the three-dimensional random-field Ising model (RFIM) will be discussed and compared to corresponding features of the dilute axial antiferromagnet in an external magnetic field (DAFF). [1] W. Kleemann, J. Dec, V. V. Shvartsman, Z. Kutnjak, Th. Braun, Phys. Rev. Lett. 97 (2006) 065702. [2] W. Kleemann, J. Phys.: Cond. Matter 18 (2006) L253.