Magnetic‐Field‐Directed Self‐Assembly of Programmable Mesoscale Shapes

Abstract

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 (≈1015 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.

Smart Nanostructures for Cargo Delivery: Uncaging and Activating by Light

“…106,107 Self-assembly of nanoparticles can be achieved using various external stimuli such as temperature, 108 pH, 109 and the presence of biomolecules 110,111 and magnetic fields. 112 In self-assembled structures, a high level of order and intermolecular specific interactions are required. 106 …”

Thermoreversible magnetic nanochains

“…Such architectures are of interest for many applications, like drug delivery, bioanalysis, data and energy storage, sensors, and catalysis. [1][2][3][4][5][6][7][8][9][10] Recently, the magnetic field (MF)-assisted 11 self-assembly of magnetic colloids into organized nanostructures like fibers, chains, tubes, and circles [12][13][14] has attracted enormous attention. The studies demonstrated that a nanoscopic and mesoscopic orientational order can be achieved by application of an MF; however, the current strategies and the resulting assemblies do have specific stability aspects, which might be not compatible with some coveted applications.…”

Control and manipulation of nanoparticles for fabrication of metal matrix composites

“…As a result, the peak magnetic field gradient regions are located at the periphery of the protrusions [40][41][42]183]. For the deposition process, 0.2 ml of suspension is introduced on a 50 µm aluminum substrate, which is fixed on top of the patterned iron disc.…”

“…Magnetic manipulation of nanoparticles can be a promising approach to selectively deposit nanoparticles if the applied magnetic field is precisely modulated. Conventionally, magnetically directed surface-patterning has been limited to magnetic particles [40][41][42]. In this work, a novel approach has been demonstrated to manipulate not only magnetic particles but also a mixture of magnetic and nonmagnetic particles.…”

“…Magnetically directed surface-patterning has been a promising approach for direct assembly of nanoparticles in custom user-defined shapes. Magnetic nanoparticle in a spatially variable magnetic field will be driven and pulled towards the highest field gradient regions; this phenomena is called magnetophoresis [42,182]. [41].…”