ABSTRACT
Nanocrystals ..............................................................355 12.2.5 Surface Ligand Exchange and Phase Transfer ...........................355
12.3 Superstructures of Magnetic Nanocrystals ................................................356 12.3.1 Two-and Three-Dimensional Ordered Superlattices .................356 12.3.2 Colloidal Crystals of Nanocrystals .............................................361 12.3.3 Template Synthesis of Inverse Opals..........................................361
12.4 Conclusions ................................................................................................364 Acknowledgments..................................................................................................364 References..............................................................................................................364
At the nanometer scale, many chemical and physical properties of solids become dramatically dependent on size. For ferromagnetic materials, this means that below some critical size, each particle can contain only a single magnetic domain. Changes in the magnetization can no longer occur through the motion of domain walls and instead require the coherent rotation of spins, resulting in larger coercivities. For a particle size smaller than the single domain size, the spins are increasingly affected by the thermal fluctuations and originally ferromagnetic material becomes superparamagnetic.1
