TL2+ EPR STUDY OF THE DYNAMICS OF THE PROTON-GLASS TRANSITION IN RB1-X(NH4)XH2PO4

The temperature dependence of the Tl2+ EPR line shapes and second moments in Tl-doped Rb1-x(NH4)(x)H2PO4 between 160 and 10 K allows for a direct determination of the static and dynamic features of the glass transition in this system. The static features can be described by a random-field smearing of a random-bond Ising pseudo-spin-glass transition with a nominal glass temperature of T(G) = 30 K and a random-field contribution of T(f) = 60 K, whereas the dynamic features show up on a slowing down of the proton intra O-H ... O bond motion. The comparison of the theoretical and experimental line shapes provides a check of the validity of a recently developed dynamic approach to the local-polarization distribution and magnetic-resonance line shape in proton and deuteron glasses.