We investigated the dot size dependence of the magnetization reversal process in microfabricated L10-FePt (0 0 1) circular dots with perpendicular magnetization. Both the as-patterned and the post-annealed dots showed the gradual increase in coercivities (Hc) as the dot diameter (D) was reduced from 1 νm to 30 nm. The dots with D ≥ 500 nm formed a multiple domain structure at the remanent magnetization state whereas a single domain structure was observed for D ≤ 100 nm. Hc as a function of the angle between the applied magnetic field and the out-of-plane direction suggested that the magnetization reversal for D ≤ 100 nm occurred through incoherent magnetization rotation while domain wall propagation was the dominant magnetization reversal process for D ≥ 500 nm. The present results imply that local structural defects, e.g. the inhomogeneity of L10 ordering, the microfabrication damage and the distribution of the c-axis orientation of L10 ordered structure, act as sites where the magnetization vectors start to rotate, which gives rise to the incoherent magnetization rotation even in the case of small dots with D = 30 nm.
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