Automotive domain wall propagation in ferromagnetic rings

In this work, we demonstrate experimentally that spontaneous domain wall propagation in asymmetric ferromagnetic rings exists without the presence of external driving magnetic fields . Depending on the size and geometry of rings, the automation occurs by relaxation of domain walls in the onion state to the energetically favored vortex state, a process during which both walls annihilate . Micromagnetic simulations have been carried out for magnetic rings with different dimensions. Our experimentally obtained angular dependences of spontaneous domain wall velocities can be understood in terms of minimalization of magnetostatic energy.