Magnetic properties of large area cobalt nanomagnets

We have investigated the magnetization reversal process of cobalt nanomagnetic dot arrays with thickness t in the range from 5 to 90 nm and diameter d in the range from 150 to 250 nm. Large area cobalt nanomagnets were fabricated on Si(100) substrate using deep ultra-violet lithography at 248 nm exposure wavelength. We observed that the magnetic properties of the nanomagnets strongly depend on the thickness and diameter of Co dots due to the effect of the demagnetizing field. The onset of the formation of a magnetization vortex at remanence was found at a phase boundary of thickness and size (e.g., t = 20 nm, d = 250 nm; t = 40 nm, d = 150 nm). Above this boundary, vortex annihilation and nucleation fields markedly varied with the thickness and diameter of the dots. Our experimental results are in good agreement with a simple micromagnetic modelling.