Ni80Fe20 nanodisks by nanosphere lithography for biomedical applications

Abstract

A novel nanofabrication technique based on self-assembling of polystyrene nanospheres and aimed to obtain magnetic nanodisks suspended in ethanol is here presented. Free-standing Ni80Fe20 disks having lateral dimension around 650 nm and thickness 30 nm were obtained by using nanosphere lithography on a sputtered continuous thin film. The multi-step nanofabrication process will be explained, in detail. The process end-product can be used as suitable magnetic carriers having nearly monodispersed size and simultaneously displaying high saturation magnetization and low-coercivity. Magnetisation reversal has been studied by room-temperature hysteresis loop measurements in either dot arrays attached on a substrate or in liquid-dispersed free-standing nanodisks. In both samples, the reversal is marked by magnetic vortex nucleation/annihilation. Such a behavior is confirmed for Ni80Fe20 dot arrays by measuring magnetic domain configuration, while numerical simulation is used for confirming magnetization reversal process in nanodisks.