Direct observation of individual Barkhausen avalanches in nucleation-mediated magnetization reversal processes

We report the scaling behavior of Barkhausen avalanches [H. Barkhausen, Z. Phys. 20, 401 (1919).] along the hysteresis loop of a CoCrPt alloy film with perpendicular magnetic anisotropy for every field step of 200 Oe. Individual Barkhausen avalanches are directly observed via soft x-ray microscopy with a spatial resolution of 15 nm. The Barkhausen avalanches exhibit a power-law scaling behavior, where the scaling exponent of the power-law distribution drastically changes from 1 +/- 0.04 to 1.47 +/- 0.03 as the applied field approaches the coercivity of the CoCrPt film. We infer that this is due to the coupling of adjacent domains.