Analysis and Control of the Initial Electrodeposition Stages of Co-Pt Nanodot Arrays

We have fabricated Co-Pt nanodot arrays by combining electrodeposition with electron beam lithography (EBL) for applications in ultra-high density magnetic recording media, such as bit-patterned media (BPM). In this work, we analyzed the initial nucleation and growth of Co-Pt inside nanopores to achieve nanodot arrays with high deposition uniformity, as well as magnetic properties. At −900 mV (vs. Ag/AgCl), multiple nuclei of 2.0-3.0 nm in size were randomly distributed, even in nanopores with a 10 nm diameter, which could result in a lack of uniformity in the magnetic properties. The number of nuclei was then reduced by applying a less negative potential (>−700 mV vs. Ag/AgCl) to deposit a single nucleus inside each nanopore. As a result, a single grain of 5.0-10 nm in size was successfully deposited inside the nanopore, which could induce uniform magnetic properties in each nanodot. In addition, at less negative potentials, the coercivity of the Co-Pt films increased, which was induced by the epitaxial-like growth of Co-Pt from the Ru substrate. Cross-sectional TEM analysis suggested that Co-Pt deposited with a less negative potential was single crystalline with uniform hcp lattice fringes in the direction perpendicular to the Ru interface, indicating the formation of highly uniform nanodot arrays with high perpendicular magnetic anisotropy.