Depinning of Domain Walls by Magnetic Fields and Current Pulses in Tapered Nanowires With Anti-Notches

The influence of the size of anti-notches on the domain wall propagation in Permalloy nanowires with edge taper is investigated. The critical magnetic fields and current pulses required for a domain wall to pass a symmetrical circular anti-notch obstacle were estimated by high-resolution in-situ Kerr microscopy experiments and by micromagnetic simulations. The nanowires, made using electron beam lithography and ion beam etching, had an average width of 220 nm and the anti-notches consisted of circular features that increased the wire width from 5% to 35%. The critical magnetic flux densities for domain walls to pass the obstacles increased with anti-notch diameter, from 0.6 mT to 3.4 mT in the simulations and 0.3 mT to 1.5 mT in the experiment. The critical current densities ranged from $0.5 \times {10^{12}}\ \text{A/m}^{2}$ to $10 \times {10^{12}}\ \text{A/m}^{2}$ in the simulations, with a strong dependence on the domain wall type, but the experiment yielded higher critical current densities of $6 \times {10^{12}}\ \text{A/m}^{2}$ to $25 \times {10^{12}}\ \text{A/m}^{2}$ .