Molecule-regulated magnetism at surfaces: from metal-organic network to molecule/ferromagnetic semiconductor hybrids

For two very different systems, namely single magnetic atoms at surfaces and ferromagnetic (Ga,Mn)As thin films, potentials of molecular coordination to influence magnetic properties are discussed.

Metal-organic networks where single 3d metal atoms are forced into a 2D regular array by molecule spacers mark the limit of non-ferromagnetic systems where the magnetic properties of each magnetic center is driven by ligand field effects. Lateral coordination with the molecular ligands yields unsaturated yet stable coordination bonds, which enable chemical modification of the electronic and magnetic properties of the 3d atoms independently from the substrate. The easy magnetization direction of the 3d centrer can be switched by oxygen adsorption, thus opening a way to control the magnetic anisotropy in supramolecular layers akin to that used in metallic thin films.

Also in ferromagnetic semiconductor epilayers magnetic properties can be influenced by molecules, although the physics behind the effect is entirely different. We observe that the adsorption of flourescein molecules and its derivates on thin film surfaces enable the manipulation of magnetic properties like the Curie temperature and the coercivity of (Ga,Mn)As. Moreover, the effect is partly reversible under the influence of light. The effects are discussed in terms of changes in the (Ga,Mn)As carrier density.