Ferromagnetism in germanium clathrate: Ba8Mn2Ge44

A unique magnetic nanosystem, constructed from Ge-20 dodecahedrons and Mn, is presented, which shows a ferromagnetic transition around 10 K. In this s ystem with the formula Ba8MnxGe46-x (x=1-2), the Mn atoms can be incorporat ed with accurate control in position of the crystal lattice. The spontaneou s magnetization is approximately linearly proportional to the amount of Mn introduced and is maximized at x=2. Magnetic measurements reveal that the d electrons are almost localized on Mn atoms but also affected by conduction electrons spreading over the clathrate network. (C) 2000 American Institut e of Physics. [S0003-6951(00)04547-2].