Nonlithographic fabrication of 25 nm magnetic nanodot arrayswith perpendicular anisotropy over a large area

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm 2 coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO 2 dot arrays formed on a Si wafer. At first, arrays of the SiO 2 dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO 2 dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO 2 dots are about 24, 43, and 17 nm, respectively. Then { Co ( 0.4 nm ) / Pt ( 0.08 nm ) } 8 MLs with a 3 nm Pt buffer layer is deposited onto the SiO 2 dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO 2 substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner-Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array.