Nuclear Magnetic Relaxation and Atomic Diffusion in Aluminum Alloys

The rotating-frame nuclear magnetic relaxation time $T_{1\rho }$ and local field $H_L$ have been measured for ${\mathrm{Al}}^{27}$ in a series of dilute aluminum-base alloys and in pure Al. The local field in the alloys is found to include both a magnetic dipole contribution, discussed previously by Slichter et al., and an electric quadrupole contribution. The latter is a direct consequence of solute perturbations of the structure and is of particular interest here. We have measured $T_{1\rho }$ between 24 and 660°C and associated it with time fluctuations of both the magnetic-dipolar and electric-quadrupolar interactions. From the magnitude and temperature dependence of the quadrupolar contribution, the solute atomic jump rate is estimated. The energy of migration for Zn, Mg, and Ag solutes is found to be much smaller than that of Al in aluminum metal.