Nuclear Relaxation in Aluminum

Nuclear spin-lattice relaxation times $T_1$ and phase memory times $T_2$ have been measured in 99.99% pure aluminum foil from 77°K to the melting point by the spin-echo method. At high temperature the line narrows due to self-diffusion, as previously observed by Seymour. The temperature dependence of the narrowing gives an activation energy of self-diffusion $E_D$ of 1.4±0.1 ev. From the measured "narrowing temperature" and Nowick's theoretical estimate of $D_0$, the same value of $E_D$ is found. As predicted theoretically, measurements show that $T_1$ arises from interaction with conduction electrons and is inversely proportional to temperature from 1°K to 930°K. At the highest temperatures, an unknown line broadening mechanism is found which is believed to represent quadrupole coupling to strain fields of dislocations. The measurements were made feasible only through the use of a phase-coherent detection system, a description of which is given.