Spin-Lattice Relaxation in Imperfect Cubic Crystals and in Non-cubic Crystals

Abstract

An examination is made of the spin-lattice relaxation in the solid state of nuclei whose energy level spacings in a magnetic field are rendered unequal by quadrupole interactions with the crystalline electric field. Attention is directed to two special cases: (1) when the main magnetic field is suddenly increased from zero, and (2) after saturation of the central line of the resonance spectrum; in the case of imperfect cubic crystals this is the only observed line. In general, 2I relaxation times characterize the relaxation behaviour, though in the two special cases the effective number is reduced. Detailed calculations of the relaxation behaviour have been made for spin number fraction three-twos and fraction five-twos for a quadrupolar relaxation mechanism. The behaviour in the two special cases differs and to a degree which depends on the relative strength of quadrupolar relaxation by transitions involving Δm = 1 and 2. The relevance of the results to the experiments of Day and Squire on potassium iodide is discussed. Magnetic relaxation is also treated and an expression is found for the 2I relaxation times.