Exchange interaction between electric current and magnetic domain wall containing Bloch lines

Bloch lines are boundaries between regions of a magnetic domain wall with opposite chiralities. An electric current exerts a force on Bloch lines through the s-d exchange interaction, in metallic ferromagnets. This large ‘‘s-d gyroscopic force’’ is normal to the drift velocity ve of the electron gas and to the Bloch line itself. We consider a current crossing a plane domain wall which contains Bloch lines, all of the same sense of twist. At a critical value of ‖ve‖, the Bloch lines start to move along the wall. At a larger critical value, the wall itself starts to move, in the direction of ve. This should happen at current densities ≂106 A/cm2, for Bloch walls in Ni-Fe films. The effective viscous coupling between electron gas and a Bloch wall is ≂100 times larger than the coupling arising from s-d exchange in the absence of Bloch lines. Small magnetic bubble domains move at right angle to the direction of a uniform current.