Molecular magnets are systems where a permanent magnetization and magnetic hysteresis can be achieved (although usually at extremely low temperatures) not through a three-dimensional magnetic ordering, but as a purely one-molecule phenomenon.
The requisites for such a system are:
The combination of these properties can lead to an energy barrier , so that, at low temperatures, the system can be trapped in one of the high-spin energy wells.
Molecular magnets exhibit an increasing product (magnetic susceptibility times temperature) with decreasing temperature, and can be characterized by a shift both in position and intensity of the a.c. magnetic susceptibility.
The first molecular magnet was a dodecanuclear manganese complex, which is held together by oxo-bridges and acetate anions.
Molecular magnets are interesting both from a purely theoretical point of view, for their quantum behavior, and from a practical point of view, as candidates for quantum computing qubits.