It turns out that assemblies of metallic nanoparticles,
"The work was inspired by the question [of] how the magnetic interaction between nanoparticles influences the magnetic behavior of the system as a whole, since such array structures are used, for example, in high density storage media," said Alexander Fabian, lead author of the study from Justus-Liebig University Giessen in Germany. "To study the influence of [the] shape of the nanoparticle assemblies, as well as the distance between them, we came up with the idea of a hierarchical design of the samples where the corresponding parameters can be varied systematically."
The round, metallic Fe304 nanocomponents Fabian and his colleagues used in their study were arranged to form differing shapes at three different length scales. Using electron beam lithography, a modernized lithography method that uses electrons to write the desired structure, they configured the nanoparticles into closely-packed shapes, such as triangles, with one side measuring about 10 particles in length. A shaped grid of the smaller-scale configurations, spaced approximately one micron apart, comprised the third hierarchy of the length scales.
"For the preparation of the samples we used lithographic methods, which allow the precise control of the distance and the shape of the nanoparticle assemblies," Fabian said. "For each of the three hierarchical levels, there are two contributions, namely the lattice-like part and the shape-like part. The high number of possibilities in sample design makes this a challenging aspect to find systems with the most promising physical properties."
Read more at: https://phys.org/news/2017-06-magnets.html#jCp
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