Nuclear Magnetic Resonance in Dilute Alloys of Mn, Fe, and Cu in Aluminum

Abstract

We have studied the nuclear magnetic resonance of ${\mathrm{Al}}^{27}$ nuclei in very dilute alloys of Mn (\ensuremath{\le}0.049 at.%), Fe(\ensuremath{\le}0.045 at.%), and Cu(\ensuremath{\le}0.30 at.%) in Al. The room-temperature results show line intensities that decrease rapidly with increasing impurity concentration. This decrease is attributed to a wipe-out from the resonance of the ${\mathrm{Al}}^{27}$ nuclei in the vicinity of the impurity, as a result of the interaction of the ${\mathrm{Al}}^{27}$ quadrupole moment with the local oscillating electric-field gradients. The experimental results indicate a wipe-out for the Al:Mn and Al:Fe alloys that is considerably larger than that for the corresponding Al:Cu alloys. This large electrostatic interaction in the case of the transition-metal impurities with unfilled $d$ shells is in agreement with the Friedel-Anderson model for such alloys, which describes the screening in terms of resonant scattering of the host-metal conduction electrons by virtual $d$ states localized at the impurity site. Using this model, one predicts an increase in the oscillating field gradient on going from Al:Cu to Al:Mn in agreement with experiment. Linewidth measurements in the liquid-helium temperature range show no temperature or magnetic-field dependence, indicating there is no local moment on the impurities.