Size dependence of the magnetization reversal process in microfabricated L 1 0 -FePt nano dots

Abstract

We investigated the dot size dependence of the magnetization reversal process in microfabricated L 1 0 -FePt (0 0 1) circular dots with perpendicular magnetization. Both the as-patterned and the post-annealed dots showed the gradual increase in coercivities ( H c ) as the dot diameter ( D ) was reduced from 1 µm 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. H c 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 L 1 0 ordering, the microfabrication damage and the distribution of the c -axis orientation of L 1 0 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.