Nuclear magnetic relaxation in liquid metals, alloys and salts

Abstract

Both the longitudinal relaxation time T 1 and the spin-spin relaxation time T 2 have been measured in liquid alloy systems with pulsed echo techniques. It has been found that T 2 is frequently shorter than T 1 in these metallic liquids and that this must be ascribed to the presence of microscopic solid surfaces from nonmetallic impurities. The influence of the electron coupled exchange interaction AI 1· I 2 on relaxation mechanisms is negligible as it is averaged out in liquid samples. This has in particular been verified in liquid thallium salts. Electric quadrupole relaxation has been observed for gallium and for sodium alloys in the liquid phase. The temperature dependence for the relaxation time in gallium is given by ( 1 T 1 ) 69 = 4.40T + 9.60 × 10 7 η T sec. The last term is caused by the quadrupole interaction due to the existence of molecular association. This association in Na-Tl alloys breaks down with increasing temperature. When the Knight shift and relaxation time T 1 for Na 23 in Tl, Hg and Pb are measured as a function of concentration, the importance of exchange and correlation corrections on the Korringa relation are evident. These corrections are themselves strongly concentration dependent in the liquid alloy due to short range order and changes in electronic structure. The temperature dependence of the shift and relaxation for Na 23 in NaTl has been measured between room temperature and 310°C. There are important changes at some solid state transitions, but the change at the melting point is small.