A new mechanism for spin-lattice relaxation of heavy nuclei in the solid state:: 207Pb relaxation in lead nitrate

A detailed investigation of the spin-lattice relaxation time, T-1, for Pb-207 in solid lead nitrate has been undertaken in an effort to understand the mechanism of relaxation. The results show that the Pb-207 T-1 is independent of magnetic field strength and inversely proportional to the square of the temperature. These are signatures of relaxation by a spin-phonon Raman scattering mechanism. Nuclear spin-lattice relaxation in solid lead salts is more efficient for sites with smaller magnetic shielding anisotropy. A coupling mechanism is proposed whereby phonons create a local magnetic field by modulating the valence electron shell motion relative to the nuclear/electron core. Literature data suggest that spin-phonon scattering is a common relaxation pathway for other spin-1/2 heavy nuclei in solids.