  Long spin relaxation times are a prerequisite for the use of spins in data
storage or nanospintronics technologies. An atomic-scale solid-state
realization of such a system is the spin of a transition metal atom adsorbed on
a suitable substrate. For the case of a metallic substrate, which enables
directly addressing the spin by conduction electrons, the experimentally
measured lifetimes reported to date are on the order of only hundreds of
femtoseconds. Here, we show that the spin states of iron atoms adsorbed
directly on a conductive platinum substrate have an astonishingly long spin
relaxation time in the nanosecond regime, which is comparable to that of a
transition metal atom decoupled from the substrate electrons by a thin
decoupling layer. The combination of long spin relaxation times and strong
coupling to conduction electrons implies the possibility to use flexible
coupling schemes in order to process the spin-information.
