Silicon clathrate with an f-electron system.

A novel crystal of Ba6Ce2Au4Si42 with Ba and Ce encapsulated into silicon-polyhedral clusters is self-assembled from the state of elemental mixture. Each atom in the crystal is arranged in its well-defined position with a nanoscale period, causing unique interactions between the conduction and the magnetic electrons originating from the independent sources of Ba and Ce, respectively. In this system, the long-distant magnetic f electrons can interact with each other through nanoscale spacing with isotropic three dimensionality, leading to the occurrence of a unique spontaneous spin ordering at 6.5 K.