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 system with the formula Ba8MnxGe46-x (x=1-2), the Mn atoms can be incorporated with accurate control in position of the crystal lattice. The spontaneous 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 Institute of Physics. [S0003-6951(00)04547-2].