Are there superspin glasses?

The effect of magnetostatic and exchange interactions on the spin structure of interacting nanoparticles and granular nanomagnets is investigated by model calculations. Effective exchange stiffnesses for inhomogeneous media are defined and determined for some geometries and interactions, and it is argued that typical ensembles of interacting small nanoparticles are micromagnetic systems rather than superspin glasses or superferromagnets. The spin structures of granular magnets often have the character of interaction domains, with far-reaching implications for magnetic phenomena such as hysteresis-loop overskewing.