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Intermittent collective dynamics of domain walls in the creep regime

13/07/2018, Salle S208, 11h

Alejandro B. Kolton

CONICET, Centro Atómico Bariloche, Argentina
Instituto Balseiro, Universidad Nacional de Cuyo, CNEA Argentina

We report a detailed study of the ultra slow domain wall motion controlling the magnetization reversal process in ferromagnetic thin films under weak applied fields, in the stationary creep regime, where the domain wall jumps between deep metastable states through thermally nucleated localized displacements. By determining the areas irreversibly reversed in consecutive time windows of different durations, we are able to resolve the non-gaussian statistics of the intermittent domain growth, for domain wall mean velocities as small as v≈1 nm/s. Our observations are quantitatively consistent with the existence of creep avalanches : roughly independent clusters with broad size and ignition-time distributions, each one composed by a large number of spatio-temporally correlated thermally activated elementary events. We experimentally confirm that the large scale geometry of domain walls is better described by depinning rather than equilibrium exponents.