DYNAMICS OF DOMAIN-WALLS IN ELASTIC FERROMAGNETS AND FERROELECTRICS

The dynamics of a ferromagnetic or ferroelectric system interacting with longitudinal and transverse acoustic waves are described by a sine-Gordon equation coupled to DAlembert equations. Within the framework of this model, we study the dynamics of 2 kinks that represent domain walls in the corresponding physical systems. It is demonstrated that driven oscillations of a kink coupled to its shadows in the acoustic subsystems are governed by a non-Newtonian equation of motion. The emission of the acoustic waves accompanying the small oscillations is investigated. Next we consider a kink-antikink collision and find a threshold for annihilation of the kink-antikink pair into a breather on account of acoustic losses. In some cases, we reveal transparency windows inside the annihilation range. The acoustic losses in the kink-antikink and kink-kink collisions are also calculated when the colliding kinks are ultrarelativistic. In the kink-kink collision the losses prove to be much smaller than in the kink-antikink one. For the dc-driven damped model, we obtain the kinks velocity-drive characteristic (VDC) and demonstrate that it has sharp steplike peculiarities at the values of the velocity equal to sound velocities, so that the VDC is hysteretic. © 1990 The American Physical Society.