²⁰⁷Pb nuclear magnetic resonance study in PbWO₄:Mn²⁺ and PbWO₄:Dy³⁺ single crystals

Abstract

In this exploration, the nuclear magnetic resonance of the $^{207}Pb$ nucleus in $PbWO_4:Mn^{2+}$ and $PbWO_4:Dy^{3+}$ Single Crystals using FT-NMR spectrometer is investigated. The line width of the resonance line for the $^{207}Pb$ nucleus decreases as temperature increases due to motional narrowing. The chemical shift of $^{207}Pb$ NMR spectra also increases as temperature decreases for both crystals. The spinlattice relaxation times $T_1$ of $^{39}K$ nucleus were calculated as a function of temperature (180 K~400 K). The $T_1$ of $^{207}Pb$ nucleus decreases as temperature increases. The dominant relaxation mechanism at the studied temperature range can be deduced as the Raman process, which is the coupling between lattice vibrations and the nuclear spins. This deduction is substantiated by the fact that the nuclear spin-lattice relaxation rate $1/T_1$ of the $^{207}Pb$ nucleus in $PbWO_4:Mn^{2+}$ and $PbWO_4:Dy^{3+}$ single crystal is proportional to $T^2$, or temperature squared. The activation energies for the $^{207}Pb$ nucleus in $PbWO_4:Mn^{2+}$ and $PbWO_4:Dy^{3+}$ single crystals are $E_a=49{\pm}1meV$ and $E_a=47{\pm}2meV$, respectively.

Figure 1. Saturation recovery traces of the ²⁰⁷Pb nucleus in a PbWO₄:Dy³⁺ single crystal as a function of delay time at 300 K.

Figure 2. Typical NMR spectra of the ²⁰⁷Pb nucleus (a) in PbWO₄:Mn²⁺ (b) in PbwO₄:Dy³⁺ single crystals at several temperatures operating at ωo/2π = 83.538 MHz.

Figure 3. Resonance frequency of the ²⁰⁷Pb nuclei in PbWO₄:Mn²⁺ and PbWO₄:Dy³⁺ single crystals as a function of temperature. The zero point is the Larmor frequency 83.538 MHz.

Figure 4. Peak to peak intensity of the ²⁰⁷Pb NMR line in PbWO₄:Mn²⁺ and PbWO₄:Dy³⁺ single crystals as a function of temperature.

Figure 5. Linewidth (FWHM) of the ²⁰⁷Pb NMR line in PbWO₄:Mn²⁺ and PbWO₄:Dy³⁺ single crystals as a function of temperature.

Figure 6. Magnetization recovery traces for ²⁰⁷Pb nuclei in PbWO₄:Mn²⁺ and PbWO₄:Dy³⁺ crystals. The curves are fitted with eq. (1).

Figure 7. Temperature dependence of the spin-lattice relaxation rate 1/T₁ for the ²⁰⁷Pb in PbWO₄:Mn²⁺ and PbWO₄:Dy³⁺ single crystals. The solid line is fits obtained by assuming Raman processes.

Figure 8. The spin-lattice relaxation time of the ²⁰⁷Pb nucleus vs. the reciprocal temperature in the experimental temperature region. The slope of the solid line represents the activation energy.