Low- and High-Temperature Magnetic Resonance and Relaxation of NaF:Mn2+

In single NaF crystals with ${10}^{18}$ to ${10}^{19}$ ${\mathrm{Mn}}^{2+}$ per ${\mathrm{cm}}^3$, and in reagent-grade powder, the ${\mathrm{F}}^{19}$ NMR line-width is studied from 300 to 1000°K, and the spin-lattice relaxation time from 2 to 1380°K (at 27 Mc/sec, with supplementary low-temperature work at 13 and 39 Mc/sec). The ${\mathrm{Mn}}^{2+}$ EPR spectrum at 9 Gc/sec, which is observed from 2 to 1000°K, with saturation-relaxation measurements below 100°K, indicates positive-ion vacancy diffusion above 250°C, and ${\mathrm{Mn}}^{2+}$ diffusion above 425°C. The NMR results yield a jump rate ${\nu }_{\mathrm{Na}}=8.8\mathrm{}\times {10}^{16}\exp [-2\mathrm{} \mathrm{eV}/kT]$ ${\sec }^{-1\mathrm{}}$ in the intrinsic region, and in the extrinsic region, an energy of activation of 0.52 eV for vacancy jumps, with a frequency factor not less than 1.1×${10}^{13}$ ${\sec }^{-1\mathrm{}}$. Negative-ion diffusion with an apparent activation energy of 3.5 eV is found above 950°C. The relaxation of isolated ${\mathrm{Mn}}^{2+}$ ions changes from the direct to the Raman process near 60°K. The calculated ${\mathrm{F}}^{19}$ relaxation rate due to this ${\mathrm{Mn}}^{2+}$ relaxation is at a maximum and of the observed order of magnitude in the range 150 to 200°K. The ${\mathrm{F}}^{19}$ relaxation from 2 to 150°K is attributed to the effects of ${\mathrm{Mn}}^{2+}$ pairs or clusters and shows a change from "rapid diffusion" to "slow diffusion" near 4°K.