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The nucleation of reversed magnetic domains in Pt/Co/AlO(x) microstructures with perpendicular anisotropy was studied experimentally in the presence of an in-plane magnetic field. For large enough in-plane field, nucleation was observed preferentially at an edge of the sample normal to this field. The position at which nucleation takes place was observed to depend in a chiral way on the initial magnetization and applied field directions. A quantitative explanation of these results is proposed, based on the existence of a sizable Dzyaloshinskii-Moriya interaction in this sample. Another consequence of this interaction is that the energy of domain walls can become negative for in-plane fields smaller than the effective anisotropy field.

International audience; We report experimental evidence of thermal effects on the displacement of vortex walls in NiFe nanostrips. With the use of nanosecond current pulses, a unidirectional motion of the magnetic domain walls towards the hotter part of the nanostrips is observed, in addition to current-induced domain wall motion. By tuning the heat dissipation in the samples and modeling the heat diffusion, we conclude that this unidirectional motion can only be explained by the presence of a temperature profile along the nanostrip. A quantitative analysis of the experiments shows that, on top of the classical thermodynamic pressure on the domain wall, another force, probably the magnonic spin Seebeck effect, is displacing the domain walls.

We study spin-diffusion effects within a continuously variable magnetization distribution, integrating with micromagnetics the diffusive model of Zhang and Li [Phys. Rev. Lett. 93, 127204 (2004)]. Current-driven wall motion is, in the steady velocity regime, shown to be adequately described by an effective nonlocal nonadiabatic parameter. This parameter is found to be 20% larger than its local counterpart for a vortex wall in a NiFe nanostrip and hardly modified for a transverse wall. This may account for the yet unexplained experimental evidence that vortex walls move more easily under current when compared with transverse walls. It is shown that this effective parameter can be derived from the domain wall structure at rest.

The magnetic susceptibility of self-organized two-dimensional Co nanodots on Au(111) has been measured as a function of their size in the 2-7 nm diameter range. We show that the activation energy for the thermal reversal displays a power law behavior with the dot volume. Atomic scale simulations based on the Heisenberg Hamiltonian show that this behavior is due to a deviation from the macrospin model for dot size as small as 3 nm in diameter. This discrepancy is attributed to finite temperature effects through the thermal excitation of spin-wave modes inside the particles.