Focused MOKE Study of Self-Assembly Nanoscale Fe $_{64}$ Ni $_{36}$ Dot Arrays

Using nanosphere lithography (NSL) technique, we have fabricated well defined triangular shaped Fe₆₄Ni₃₆ dot arrays with feature size down to 30 nm on silicon substrate. In-plane focused magneto-optical Kerr effect (MOKE) measurements show that these nanoscale dot arrays have an enhanced coercivity of around 200 Oe compared with that of the continuous thin film of 50 Oe. In combining with micromagnetic calculations, we found that the magnetization process follows two steps, the rotation of the top corner and then a switching of the bottom base, which controls the coercivity of the dots.