Magnetic vortices in tridimensional nanomagnetic caps observed using transmission electron microscopy and magnetic force microscopy

Magnetic domain formation on three-dimensional nanostructures was investigated. Co/Pd multilayers were deposited on polystyrene nanospheres (50--1000 nm) to form a magnetic cap with variable thickness. High resolution transmission electron microscopy and magnetic force microscopy images, allied with micromagnetic simulations, were used to correlate the three-dimensional shape of the caps with their domain structures. For smaller spheres (50--100 nm), the caps are segmented into nanopillars (10 nm) oriented toward the radial direction. For larger spheres (500--1000 nm), the cap is a continuous film with the magnetization forming a vortex at the top of the cap, with a core well larger than the ones observed in planar disks.