Exchange forces between domain wall and electric current in permalloy films of variable thickness

Abstract

Wall displacements are induced by large current pulses crossing a wall, in Ni81Fe19 films. In films of thickness w<35 nm containing Néel walls, the sense of wall motion is found to be independent of the magnetization sense in the two domains adjacent to the wall, and is identical to the sense of motion of the electronlike charge carriers. This shows that the wall motion is not caused by stray magnetic fields, but rather by s-d exchange forces generated by conduction electrons. The value ≂5×107 A cm−2 of the needed current density agrees with predictions of a theory based on s-d exchange. In the case of cross-tie walls in films with 35 nm <w<86 nm, the sense of wall motion does depend on the sense of the domain magnetizations. The force of the circumferential magnetic field of the current is probably important, here.