Coercive field enhancement in Co nanodisks: Single-domain to vortex switching.

Magnetic multi-layered nanodisks (ND) show great promise as these are relatively easy to assemble and control, facilitating biological and storage applications. In the present work, Ti/Co/Nb ND were fabricated with a varying Co layer thickness between 6 and 14 nm. Using vibrating sample magnetometry and micromagnetic simulations (OOMMF), their magnetic properties were investigated. Our results reveal a peak in coercive field at a critical thickness that separates the two magnetic phases; single domain and vortex phase. This peak is characterized by a substantially larger coercive field and allows to establish an explicit phase diagram as a function of diameter and thickness of the ND. This opens the possibility to investigate such enhancement in other ferromagnetic materials too.