Magnet
Rare earth (lanthanoid) elements have a partially occupied "f" electron shell (which can accommodate up to 14 electrons). The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore, these elements are used in compact high-strength magnets where their higher price is not a concern. The most common types of rare-earth magnets are samarium-cobalt and neodymium-iron-boron (NIB) magnets.
Single-molecule magnet
The archetype of single-molecule magnets is called "Mn". It is a polymetallic manganese (Mn) complex having the formula [MnO(OAc)(HO)], where OAc stands for acetate. It has the remarkable property of showing an extremely slow relaxation of their magnetization below a blocking temperature. [MnO(OAc)(HO)]·4HO·2AcOH, which is called "Mn-acetate" is a common form of this used in research.