Domain wall pinning and controlled magnetic switching in narrow ferromagnetic ring structures with notches (invited)

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Abstract
We present a magnetoresistance study of controlled spin switching and domain wall pinning effects in mesoscopic narrow ferromagnetic Permalloy ring structures containing notches. It is found that notches create an attractive potential well for the transverse domain walls present in these structures. The strength and size of this potential well is measured and found to stretch far beyond the physical dimensions of the notch. Measuring the resistance, a minimum at remanence is found to occur when a transverse domain wall is pinned at the notch, in agreement with the results of numerical simulations of the anisotropic magnetoresistance. Applying a field in the direction corresponding to a potential well edge, a magnetic state with a very wide domain wall is stabilized, leading to a dip in the magnetoresistance at such angles. Using notches of different sizes, it is demonstrated that controlled switching is achieved, which means that the circulation direction of the vortex state can be selected.