Hierarchical geometric frustration in La3Cu2VO9
  The crystallographic structure and magnetic properties of the La3Cu2VO9 were investigated by powder neutron diffraction and magnetization measurements. The compound materializes geometric frustration at two spatial scales, within clusters and between clusters, and at different temperature scales. It is shown by exactly solving the hamiltonian spectrum that collective spins are formed on each clusters at low temperature before inter-clusters coupling operates. 
Julien Robert (LLN), Benjamin Canals (LLN), Virginie Simonet (LLN),   Rafik Ballou (LLN), C\'eline Darie (LC), Bachir Ouladd...