Schematics of dislocation movement in the presence of a magnetic field. Panel (a) shows surmounting the previous obstacle and moving forward; panel (b) displays the motions close to the obstacles, in the cases of L > L * (e) and L < L * (f), with L being the distance between dislocation and obstacles, and L * the critical one; panel (c) refers to the stay at the obstacles; panel (d) indicates the surmounting the obstacles and moving forward.