Magnetization processes in mesoscopic systems: Nucleation, magnetization reversal and hysteresis.

The magnetization nucleation mechanisms taking place in "perfect" submicronic cobalt dots obtained by means of 3D Micromagnetic simulations are shown. Attention is focused on the study of the transition from parallel-to-plane to perpendicular-to-plane magnetization occurring as the thickness of the dot is increased. Simulations show different nucleation and magnetization reversal mechanisms as thickness varies. For a 35 nm dot, nucleation of stripe domains takes place, these domains bending as a result of the need for a lateral flux closure when the applied field is reduced to zero. For 25 nm thick dots no stripe domains are present and a full inplane magnetization configuration has been obtained for which flux closure takes place with the formation of two distorted vortices at both sides of the dot.