Nucleation and propagation of domains walls in a Co∕Pt multilayer wire

Abstract

The domain wall processes in Hall bar devices patterned from Co∕Pt multilayers with perpendicular magnetic anisotropy have been studied by Kerr microscopy and extraordinary Hall effect measurements. The samples are extremely thin (<2nm) so that they show full remanence and a square hysteresis loop with a coercive field of ∼25Oe. The Kerr microscope observations of the as-patterned Hall bars have shown an uncontrolled domain wall nucleation followed by rapid propagation, without significant pinning. This shows that the nucleation field exceeds any propagation and pinning fields in these samples. Controlled domain wall nucleation by irradiation of a selected area of the Co∕Pt multilayer structure with different doses of Ga+ ions on the multilayers has been studied proving the decrease of coercivity in such irradiated areas with respect to the rest of the sample. This method can be used to lower the nucleation field below any pinning fields that exist in the sample, enabling controlled wall positioning within the Hall bar in the future.