Arrays of ordered nanostructures in Fe-Pt thin films by self-assembling of polystyrene nanospheres

Large-area arrays of dots having diameter ranging in the interval 80-400nm were obtained by polystyrene nanosphere (PN) lithography in L10-FePt thin films. Fe53Pt47 thin films (thickness 10 nm) were epitaxially deposited by rf sputtering on a MgO(100) substrate heated at 400°C to promote the formation of the L10 tetragonal phase. Patterned films were obtained by assembling PN nanospheres monolayer with starting mean diameter of 100 and 500 nm on a continuous thin film; subsequently, the PNs size has been reduced by reactive ion etching, obtaining a final dots diameter of 80 and 400nm, respectively. The patterning process resulted to disorder the tetragonal phase therefore reducing the coercive field. A post-annealing at 550 °C for 1 h resulted to be effective in re-inducing the precipitation of the ordered phase. The effect of patterning (i.e., dot diameter and mutual distance) on the magnetic properties is discussed in the light of the presence of the high-anisotropy L10 tetragonal phase, by means of both structural and magnetic characterization techniques.