  The slow dynamics and concomitant memory (aging) effects seen in nanomagnetic
systems are analyzed on the basis of two separate paradigms : superparamagnets
and spinglasses. It is argued that in a large class of aging phenomena it
suffices to invoke superparamagnetic relaxation of individual single domain
particles but with a distribution of their sizes. Cases in which interactions
and randomness are important in view of distinctive experimental signatures,
are also discussed.
