Magnetic-Field-Directed Self-Assembly Of Programmable Mesoscale Shapes

User-programmed meso-to microscale 2D shapes using magnetic nanoparticles as building blocks with magnetic-field-directed self-assembly are created. The assembly templates are magnetically recorded using perpendicular magnetic recording (PMR) media. The results demonstrate that PMR can template user-designed features in two dimensions down to 30 nm in size, i.e., the nanoparticle diameter. It has been also shown that the nanoparticles assemble onto transitions between oppositely magnetized regions in the medium. At these transitions, the magnetic field gradients are extremely large (25 MT m(-1) 2 nm above the medium) and change rapidly with height (approximate to 10(15) T/m/m within 20 nm of the surface). It is found that 30 nm diameter particles assemble into 1-2 layers with feature widths ranging from 30 to 350 nm. It is hypothesized that large lateral growth can occur because the magnetic forces parallel to the disk extend up to 150 nm on either side of a recorded transition, falling off more slowly with distance than the vertical magnetic forces. Once lateral growth saturates, a second layer of nanoparticles begins to assemble on top of the first layer, suggesting strong potential for controlling layer-by-layer assembly through appropriate design of the medium and its resulting field gradient profiles.