Nuclear magnetic resonance intensities in alloys

Abstract

The steady state magnetic resonances of 63Cu, 27A1 and 7Li have been studied in the majority constituents of the Cu-Ni, Cu-Au, Al-Zn and Li-Mg alloy systems, over wide ranges of composition, magnetic field and temperature. Nuclear electric quadrupole effects are most prominent. The line widths, shapes and frequencies can be qualitatively understood in simple cases, but the predictions of the general statistical problem have not been obtained. Initial intensity reductions in copper alloys are consistent with screening of excess charge by conduction electrons and enhancement by antishielding factors. The field gradients seem to be primarily of charge origin when there is a valence difference, but those arising from size differences can be comparable. The intensity falls markedly less rapidly above about 20 per cent solute in Cu-Ni and Cu-Au, and increases very strongly at about 40 per cent Ni. The anomalous intensity is believed to arise from non-cubic configurations of solute atoms which give rise to small field gradients at the central nucleus. The influence of order in Cu-Au on the intensity is described better by the conventional long range order than short range order, because the former distinguishes between the Cu and Au sublattices. The predictions are compared with effects of heat treatment.