Thermally activated avalanches: Jamming and the progression of needle domains

Abstract

Large-scale computer simulations of a simple model with a square-lattice topology, a small shear deformation (${4}^{\ifmmode^\circ\else\textdegree\fi{}}$ shear angle), and open (free) boundary conditions show that domain boundary movements under adiabatic strain deformation lead to Vogel-Fulcher behavior at high temperatures. The activation energy is independent of temperature and details of the twin patterns. Below the Vogel-Fulcher temperature, no thermal activation was found and the time evolution of the domain pattern becomes athermal. The movement of domain boundaries is now dominated by the nucleation and growth of needle domains. Their movement occurs in fast jerks. The probability to observe jerks follows a power-law spectrum with energy exponents close to $\ensuremath{\alpha}\ensuremath{\approx}2$. At even lower temperatures, the boundary kinetics becomes erratic even in our large (${10}^{6}$atoms) system. The lateral movement of twin walls is found for our thin twin walls ($w=3$ layers) to operate by kinks which propagate along the twin wall. The needle domains nucleate either from the surface or from other existing twin walls. Intersections of twin walls constitute pinning centers which impede the free movement of the kinks in the walls. These intersection points then act as a pattern of intrinsic, self-induced defects which lead ultimately to the power-law distribution of the crackling noise of the domain walls.