Morphology-dependent multi-step ferromagnetic reversal processes in Co thin films on crescent-shaped antidot arrays

We report on the anomalous hysteresis loops and isolation of nanodomains in Co films deposited on hexagonally ordered antidot arrays produced by anodization of alumina templates. Using the Magneto-optic Kerr effect and vibrating sample magnetometry, we analyzed how the magnetization varied with depth from the antidot surface. Our results show that the multi-step reversal of the hysteresis loops was associated both with the feature size of the antidot array and with the growth morphology. Magnetic force microscopy showed that as the pore diameter increased, the magnetic domains became more distinct and separate, following the topography of the hexagonal array. The porous regions exhibited highly stable vortex-like magnetic domains, and the perpendicular magnetic moments observed around the circumference of magnetic nanotubes. These domain configurations indicate that the three-dimensional magnetic profile was caused by the growth morphology.