Beyond the compact magnetic domain wall.

Domain wall dynamics in wide submicrometer wires is investigated to understand the fundamental mechanisms that limit wall mobility, both experimentally by magneto-optical Kerr effect and by micromagnetic simulations. It is found that the dynamic domain wall structure departs significantly from the current description of a compact entity when evolving along the wire. The wall is composed of several substructures, each one propagating and evolving in a different dynamic regime with very different velocities.

Dependence of domain-wall depinning threshold current on pinning profile.

We have investigated the threshold current density required for depinning a domain wall from constrictions in NiFe nanowires, which give rise to pinning potentials of fixed amplitude but variable profile. We observed it to vary linearly with the angle of the triangular constriction. These results are reproduced using micromagnetic simulations including the adiabatic and nonadiabatic spin-torque terms. By curve-fitting the calculated variations to the experimental results, we obtain the nonadiabaticity parameter beta=0.04(+/-0.005) and current spin polarization P=0.51(+/-0.02).

Control of domain wall polarity by current pulses.

Direct observation of current-induced propagation of purely transverse magnetic domain walls with spin-polarized scanning electron microscopy is reported in Fe30Ni70 nanowires. After propagation, the domain walls keep their transverse nature but switch polarity in some cases. For uniform Ni70Fe30 wires, the effect is random and illustrates domain-wall propagation above the Walker threshold. In the case of Ni{70}Fe_{30}/Fe wires, the transverse magnetization component in the wall is entirely determined by the polarity of the current pulse, an effect that is not reconciled by present theories even when taking into account the nonuniform Oersted field generated by the current.