Anomalously high velocity of the domain walls driven by the electric current in bilayer permalloy-niobium structures

The motion of domain walls in bilayer permalloy-niobium strips under the effect both of the electric current flowing along the strips and of the applied magnetic field has been studied in a wide temperature range. On cooling from room to liquid helium temperature, the same structures exhibit hundredfold growth in the velocity of domain walls whose motion is induced by the transport current. At the same time, the hundredfold decrease in this velocity and the increase in the coercivity is observed if the motion is driven by the applied magnetic field. It is found that the maximum velocity of domain walls far exceeds the Walker limit.