High-field 19F NMR relaxation studies in the superionic conductor Mn:PbF2.

Abstract

The $^{19}\mathrm{F}$ NMR spin-lattice relaxation rate ${T}_{1}^{\mathrm{\ensuremath{-}}1}$ in ${\mathrm{Mn}}^{2+}$:${\mathrm{PbF}}_{2}$ was measured in applied fields such that \ensuremath{\gamma}${H}_{0}$>A, the ${\mathrm{Mn}}^{2+}$${\mathrm{\ensuremath{-}}}^{19}$F transferred hyperfine interaction. The results obtained generally agree with the predictions of the impact-model theory of nuclear relaxation in magnetically tagged superionic conductors. It is shown that for reasonable choices of the isotropic ${A}_{s}$ and anisotropic ${A}_{p}$ $^{19}\mathrm{F}$ transferred hyperfine interaction and the ${\mathrm{Mn}}^{2+}$ electron spin-lattice relaxation rate ${\ensuremath{\tau}}_{\mathrm{SL}{}^{\mathrm{\ensuremath{-}}1}}$, one can obtain agreement between theory and experiment at both low (T550 K) and high (T>700 K) temperatures, but not in the range 550T700 K, using the conductivity-determined hopping rate. This discrepancy is used to determine an ``NMR effective hopping rate.''