The
Lanthanides are commonly known as
rare earth metals, presumably due to their
scarcity. They should not be confused with the higher-numbered (though similarly offset in the
periodic table, a likely source for the confusion)
actinide series, which are all radioactive; the only
radioactive lanthanide is element 61,
Promethium.
The "rare earth" lanthanide metals can be used to make very powerful magnets, since they have strong paramagnetic properties. When cooled to low temperatures, the rare earths have ferromagnetic properties as well.