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DF: Dielektrische Festkörper

DF 11: Electric, Electromechanical and Optical Properties II

DF 11.1: Hauptvortrag

Freitag, 31. März 2006, 10:50–11:30, M{\"U}L Elch

Universal domain wall dynamics in ferroics and relaxors — •Wolfgang Kleemann — Angewandte Physik, Universität Duisburg-Essen, Duisburg, Germany

Domain walls in random ferroic media reveal different dynamic modes. The complete series under external ac fields at decreasing frequencies, f, segmental relaxation, creep, slide and switching, is observed in quantum ferroelectric SrTi¹⁸O₃ [1], superferromagnetic CoFe/Al₂O₃ multilayers [2], and ultrathin ferromagnetic trilayers Pt/Co/Pt [3]. Dynamic scaling explains the transition from Cole-Cole-type segmental relaxation to creep with inverse power law dispersion as observed in periodically-poled KTiOPO₄ at f_m = f_m0exp(- E/k_BT), f_m0 = 3× 10⁹ Hz and E = 0.6 eV [4]. Segmental relaxation and creep are also observed in the uniaxial relaxor Sr_0.61Ba_0.39Nb₂O₆ [5], where wall pinning due to charge disorder-induced random electric fields is also responsible for the occurrence of nanopolar regions in the paraelectric regime, T > T_c ≈ 350 K. Their interfaces with the paraelectric environment reveal similar dynamic modes as pinned ferroic domain walls. [1] J. Dec et al., Ferroelectrics 298 (2004) 163. [2] X. Chen et al., Phys. Rev. Lett. 89 (2002) 137023. [3] O. Petracic et al., unpublished. [4] Th. Braun et al., Phys. Rev. Lett. 94 (2005) 117601. [5] W. Kleemann et al., Phys. Rev. B 65 (2002) 220101.