Switching processes and switching reproducibility in ferromagnetic ring structures

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Abstract
We present an experimental study of the reproducibility of the different switching processes occurring in rings. Using superconducting quantum interference device and magnetoresistance measurements, we can measure hysteresis loops of arrays of rings and single structures at varying temperatures and thereby separate the influence of thermal excitations and defects (extrinsic and intrinsic). We find that the temperature dependence of the switching fields and their distributions can be correlated with the different physical processes occurring during different transitions. Measurements of the angular dependence of the switching fields of a single ring allow us to distinguish the contributions of extrinsic and intrinsic defects to the switching field distributions and, counterintuitively, it is established that transitions involving nucleation processes are less prone to defects and thermal excitations than processes involving domain-wall or vortex core depinning and propagation.