Using reverse micelles as nanoreactors facilitates the preparation of bimetallic Cr-III-Ni-II, cyanide-bridged nanoparticles that behave as superparamagnets with a blocking temperature of 5.5 K. The Figure presents a plot of magnetization vs. field for various temperatures. Redispersion in an organic solution allows the articles to be diluted in a polymer matrix (inset of Figure) leading to a shift of the blocking temperature down to 2 K.