Researchers from the US Ames Laboratory discovered that rare-earth minerals dysprosium and gadolinium react strongly with graphene, while lead does not. The researchers deposited a few atoms of each material on graphene, which then started to move on their own (self-assembly) - to form "islands" on the graphene. The lead atoms moved quickly when cooled down, while the dysprosium moved slowly, even when heated up.
The fact that lead moved quickly means that it does not have a strong interaction with the graphene sheet. The rare-earth atoms does have a strong inteaction - they act like tiny magnets. It turns our that these tiny islands are good nanomagnets. This discovery may lead to applications in magnetic memory, for example.