Current-induced domain wall propagation and transformation

The current-driven motion of domain walls is the basis of several new concepts of radically new magnetic memory and logic devices. Although domain wall devices have been under consideration for more than 50 years, there are fundamental difficulties in manipulating domain walls with magnetic field: Neighboring walls, for instance, move in opposite directions. This is entirely different for current-driven wall motion. The current in the ferromagnetic nanowire becomes spin-polarized, and the spins exert a torque on the domain wall, which can be large enough to move the wall. Adjacent walls in this case move in the same direction, determined by the current.

We have studied the propagation of domain walls in NiFe nanowires with electric pulses in the microsecond range for both the vortex type [1,2] and the transverse type, demonstrating domain propagation up to 15 m/s. Furthermore, our unique spin-SEM setup makes it possible to study the transformation of the domain wall after current pulses. We found that vortex walls transformed after several pulses into the transverse state and then stopped propagating [1,2].

We also observed that transverse domain walls, which are encountered in narrower nanowires, kept their characteristic shape after a current pulse.

In part of our efforts in this field, we developed an extension for the OOMMF micromagnetic simulations framework, which allows the simulation of current-induced effects on magnetic domain wall.

 References

[1]	M. Kläui, P.-O. Jubert, R. Allenspach, A. Bischof, J. A. C. Bland, G. Faini, U. Rüdiger, C. A. F. Vaz, L. Vila and C. Vouille, Direct observation of domain-wall configurations transformed by spin currents, Phys. Rev. Lett. 95, 026601 (2005).
[2]	P.-O. Jubert, M. Kläui, A. Bischof, U. Rüdiger and R. Allenspach, Velocity of vortex walls moved by current, J. Appl. Phys. 99, 08G523 (2006).