ELECTRON-PARAMAGNETIC-RESONANCE INVESTIGATIONS OF MGSIF6-CENTER-DOT-6H(2)O-MN2-CRYSTALS( SINGLE)

EPR studies were performed on MgSiF6 . 6H(2)O single crystals using Mn 2+ paramagnetic probes substituted for Mg2+ ions. The spin-Hamiltonian parameters (SHPS) are determined accurately for the different phases: the monoclinic phase below T-c = 301 K, the rhombohedral phase above T-0 = 370 K and the intermediate phase between T-c and T-0. The sets o f SHPS are interpreted in the light of structural changes between thes e phases. The EPR line features in the intermediate phase are analysed in the framework of a static and an order-disorder model. We interpre t the EPR spectrum behaviours around T-0 - 20 K as the occurrence of a crossover between static and dynamic disorder in the material.