Coercive field enhancement in single-domain to vortex switching in magnetic Co nanodisks

The impressive magnetic properties at the nanoscale have given special attention to the magnetic nanodisks (ND). Among the most prominent applications stand data storage or magneto plasmonic devices. For the present work, we have focused in Cobalt (HCP), using the colloidal lithography technique we have obtained circular ND varying the Cobalt layer from 5-15nm and diameters of 170nm. Here we have studied experimentally, by vibrating sample magnetometry (VSM). Theoretically studies of nanodisks by micromagnetic simulations (OOMMF) have been performed in a wide range of thicknesses between 5-15 nm and diameters between 100-500 nm. From the hysteresis loop measurements, the coercive field as a function of thickness shows an unexpected peak at a critical thickness. Simulations predict the appearance of such peak and indicate that is strongly dependent on the dimensions of the Co layer. The fabrication and subsequent magnetic measurements confirm those results, such as the presence of magnetic single domain and vortex states in the ND. Finally the critical thickness where the hysteresis loop shows the highest coercive field turns out to be the value of thickness which separates the single domain state from the vortex state, due to dipolar exchange energies, and shape anisotropy.