Nuclear magnetic resonance in random fields: cluster formation and local dynamics of a deuteron glass

NMR data show that the deuteron "pseudo spin-glass" transition in Rbi- X(ND4)*D2P04 is not just a simple kinetic slowing down process but is characterized by a gradual condensation of randomly polarized clusters as expected if we deal with a percolation transition in eigenstate space. The results provide novel information on the temperature dependence and distribution of local random fields and their dynamics. The spin-lattice and motional-narrowing data further suggest that the "pseudospin" O- D- -O deuteron intrabond motion determines the freezing dynamics.