Magnetic properties of Mn-doped Ge46 and Ba8Ge46 clathrates

We present a detailed study of the magnetic properties of unique cluster assembled solids, namely Mn-doped Ge-46 and Ba8Ge46 clathrates using density functional theory. We find that ferromagnetic ground states may be realized in both compounds when doped with Mn. In Mn2Ge44, ferromagnetism is driven by hybridization-induced negative exchange splitting, a generic mechanism operating in many diluted magnetic semiconductors. However, for Mn-doped Ba8Ge46 clathrates incorporation of conduction electrons via Ba encapsulation results in RKKY-like magnetic interactions between the Mn ions. We show that our results are consistent with the major experimental observations for this system.