Nuclear magnetic resonance in intermetallic compounds

Abstract

The nuclear magnetic resonance absorption of aluminium and cobalt has been studied in the intermetallic compounds NiAl, CoAl, FeAl, Al₂NiCo, Al₂FeCo, Al₂FeNi and CoTi. The intensity measurements indicate a high degree of order in all the compounds studied, particularly NiAl and CoAl. The relatively large values of intensity at compositions appreciably different from the equiatomic value for these two series of compounds is accounted for by assuming that a large volume of the material remains ideally ordered and that the excess atoms, or vacancies, are not distributed at random. The Knight shift for ²⁷Al in the equiatomic compounds NiAl, CoAl and FeAl is +0·063 ± 0·003%, +0·034 ± 0·003%, and −0·390 ± 0·005% respectively, and for ⁵⁹Co in CoAl and CoTi the values are +0·110 ± 0·003% and +2·250 ± 0·003%. The Knight shift is independent of composition in the β′ phase region for NiAl and FeAl, but varies in CoAl becoming negative at lower values of aluminium content. The negative Knight shifts are explained by an exchange polarization interaction between unfilled d shells and core electrons.