Combining self-assembled SiO{sub 2} nanoparticle arrays with magnetic film deposited onto the particles, enables an elegant possibility to create magnetic nanostructure arrays with defined magnetic properties. In this regard, materials such as CoPt alloy are of particular interest due to their large magnetic anisotropy required for thermal stability in the high density magnetic recording applications. In order to induce high perpendicular magnetic anisotropy in CoPt alloys, the L1{sub 0} phase with (001) texturing is required. For this purpose, a 10 nm thick MgO(001) seed layer was introduced. Results on planar amorphous SiO{sub 2} substrates reveal an uniaxial out-of-plane magnetic anisotropy and saturation magnetization for the CoPt alloy grown at 450 C of about 5x10{sup 5} J/m{sup 3} and 800 kA/m. These properties were transfered to CoPt alloy deposited onto arrays of SiO{sub 2} particles with diameters down to 50 nm. The formed CoPt nanocaps are in a magnetic single domain state with a large out-of-plane coercivity, which increases with decreasing particle size. In this presentation, the structural and magnetic properties are discussed and compared to the planar film.