Nanocrystallites embedded in substrates (granular materials) prepared
by ion implantation have many unusual properties in comparison with bu
lk materials. Features are found such as high magnetic coercivity, siz
e effect of the effective magnetic moment per atom, dependence of the
interface magnetic hyperfine field on the Co concentration, nonlinear
photoluminescence as well as charge transfer. We show that CEMS and em
ission Mossbauer spectroscopy are powerful tools for studying these gr
anular systems.