Saturation narrowing, dispersion signal saturation and spin-lattice relaxation NMR measurements in solids

Abstract

Nuclear magnetic resonance lock-in absorption mode and dispersion mode spectra of polycrystalline samples of calcium fluoride, potassium caproate (KC 6), and lithium stearate (LiC 18) have been obtained at room temperature for various levels of saturation. The linewidths narrow and the line shapes change in both the absorption and dispersion mode spectra on saturation. This behavior is indicated by Redfield theory Phys. Rev. 98, 1787 (1955), and agrees with the magnetic resonance saturation theory of Provotorov ( Zh. Eksp. Tear. Fiz. 41, 1582 (1961), Sov. Phys.-JETP 14, 1126 (1962)). When the saturation level is high, absorption of energy from the modulation field (modulation saturation) can also perturb the lock-in spectra. An important prediction of Provotorov theory is that the mechanism causing saturation narrowing does not affect the signal at the center of resonance (within certain limiting conditions) and so the signals at this point are expected to saturate according to the normal saturation factor: Z(0) = [ I + γ 2 H 1 2 πg(0) T 1] −1. Progressive saturation plots of the lock-in dispersion signal u 1(0) in CaF 2, KC 6, and LiC 118 verify this prediction and yield spin-lattice relaxation time ( T 1) values of 0.42, 4.I, and 17.4 sec, respectively.