Thermal relaxation in soft magnetic patterned elements

The thermal decay of Ni80Fe20 nominally rectangle bar arrays with different sizes (1×5, 1×10, 1×15, and 2×10 μm2) and thicknesses (7.9, 10.0, 18.3, and 43.5 nm) has been studied. Observation of the remanent domain structure using magnetic force microscopy showed that the bars were uniformly magnetized with simple end curling in the thinnest samples, with simple end curling and end vortices in the intermediate samples, and with only end vortices in the thickest samples. The 1 μm wide elements switched abruptly from the “up” polarized domain to the “down” polarized domain state during reversal. Time-dependent coercivity measurements were analyzed using Sharrock’s formula to extract the intrinsic switching fields and the thermal sensitivity factors. The latter increased from 113 to 243 in the 7.9-nm-thick samples to 167–628 in the 18.3 nm samples, but decreased precipitously to 66–94 for the 43.5 nm samples. This behavior is correlated to the element’s size and the end domain structure.