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

A detailed investigation of the spin-lattice relaxation time, T-1, for Pb-2 07 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 independe nt of magnetic field strength and inversely proportional to the square of t he temperature. These are signatures of relaxation by a spin-phonon Raman s cattering mechanism. Nuclear spin-lattice relaxation in solid lead salts is more efficient for sites with smaller magnetic shielding anisotropy. A cou pling mechanism is proposed whereby phonons create a local magnetic field b y modulating the valence electron shell motion relative to the nuclear/elec tron core. Literature data suggest that spin-phonon scattering is a common relaxation pathway for other spin-1/2 heavy nuclei in solids.