To understand the magnetic configuration of the low dimensional material, we also perform the micromagnetic simulation utilizing the OOMMF code from NIST. With the simulator, we revisit the magnetic phase diagram of Co nanodots in hexagonal shape (Fig.a).In contrast to previous 3 phase diagram, we find there is a broad region where both the single domain state and vortex state can coexist. We also investigate the domain wall width reduction effect under the nanometer size constrained in Co system (Fig. b)