  The author reviews the present understanding of the hole-mediated
ferromagnetism in magnetically doped semiconductors and oxides as well as the
origin of high temperature ferromagnetism in materials containing no valence
band holes. It is argued that in these systems spinodal decomposition into
regions with a large and a small concentration of magnetic component takes
place. This self-organized assembling of magnetic nanocrystals can be
controlled by co-doping and growth conditions. Functionalities of these
multicomponent systems are described together with prospects for their
applications in spintronics, nanoelectronics, photonics, plasmonics, and
thermoelectrics.
