Magnetization reversal in nano-structures by domain wall propagation under magnetic field and electrical current

The magnetic domain wall is an essential concept for understanding magnetization reversal in a magnetic film or nano-structure, and can be involved in writing and transmitting information in a nano-device. It was shown theoretically that, in a defect-free magnetic nano-structure, confinement can strongly affect domain wall propagation under a magnetic field and/or a spin-polarized current. This was illustrated by a magneto-optical microscopy study of domain wall propagation in ultrathin Pt/Co/Pt films with perpendicular anisotropy. In these films, nano-tracks were patterned and irradiated at a very low dose with helium ions. These devices were shown to be model systems, ideal for the study of domain wall propagation under field, and appeared as promising systems for studying spin-transfer-induced propagation. However, for the whole range of the current pulses that we injected into these tracks, none of the experimentally observed propagation effects could be ascribed to spin transfer. Following a quantitative evaluation of the current and its polarization in the cobalt layer, this was attributed to an unfavorable balance between Joule heating and spin transfer. We also built a high resolution polar Kerr magnetometer which uses a highly focused laser beam. Its outstanding resolution, stability and sensitivity are well-adapted for the study of ultrathin magnetic nano-structures with perpendicular anisotropy, down to submicron scales. (author)