ON THE LIMITING VELOCITY AND FORCED MOTION OF FERROMAGNETIC DOMAIN-WALLS IN AN EXTERNAL-FIELD PERPENDICULAR TO THE EASY-MAGNETIZATION AXIS

A theory is constructed for the dynamics and braking of domain walls i n ferromagnets when a magnetic field is applied perpendicular to the a xis of easy magnetization (i.e., a transverse field H-perpendicular to ). The theory is valid for velocities upsilon up to the limiting domai n wall velocity upsilon(c). The Landau-Lifshitz equations in the dissi pationless approximation are used to investigate the motion of domain walls and the change in the character of the wall motion as its veloci ty upsilon approaches upsilon(c). The force acting on a domain wall du e to viscous friction is calculated within the framework of generalize d relaxation theory, and the dependence of the domain wall velocity up silon on the forcing field H-z is investigated. Calculations of the br aking force show that the contributions of various dissipation mechani sms to the friction force have different dependences on the domain wal l velocity, which affects the form of the function upsilon=upsilon(H-z ). The shapes of the curves upsilon(H-z) differ very markedly from one another for different values of the held H-perpendicular to. The theo ry developed here can be used to describe the experimental results, in particular the almost linear behavior of upsilon=upsilon(H-z) for sma ll H-perpendicular to and its strongly nonlinear behavior when H(perpe ndicular to)similar to H-a, whereas these data cannot be reconciled wi thin the standard theory based on relaxation terms of Hilbert type. (C ) 1997 American Institute of Physics. [S1063-7761(97)01409-1].