Superstructures of self-assembled cobalt nanocrystals

Uniform three-dimensional superstructures of spherical cobalt nanocrystals are produced by the interplay between dipolar interaction and applied magnetic field. An anomalous low-temperature magnetic behavior is observed, indicating that uncompensated surface spins become ordered below 10 K, as evidenced by the presence of two magnetic phases that superimpose in hysteresis loops as compared to measurements at 20 K. The approach discussed here provides a framework for applications such as high-performance mesomagnets, microelectronic and magnetic devices fabrication, and can be extended to other nanocomposite materials fabrication if cobalt particles can act as carriers for other nanoparticles. © 2004 American Institute of Physics. @DOI: 10.1063/1.1723687#