NMR spin-echo spectra of icosahedral quasicrystals

Abstract

We report ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$ spin-echo spectra for the icosahedral quasicrystals ${\mathrm{Al}}_{86}$ ${\mathrm{Mn}}_{14}$ and ${\mathrm{Al}}_{72}$ ${\mathrm{Si}}_6$ ${\mathrm{Mn}}_{22}$ and for the amorphous and equilibrium crystalline forms of ${\mathrm{Al}}_{86}$ ${\mathrm{Mn}}_{14}$. The distribution of local electric-field-gradient magnitudes at the Al sites in icosahedral ${\mathrm{Al}}_{86}$ ${\mathrm{Mn}}_{14}$ is only slightly narrower than in the amorphous form, but the local asymmetry in the former is significantly restricted to lower values. A corresponding degree of order is not detectable for the Mn sites in icosahedral ${\mathrm{Al}}_{86}$ ${\mathrm{Mn}}_{14}$ for which the distribution of the local environments is comparable with that observed in amorphous material. Broad distributions are also inferred for both Al and Mn sites in icosahedral ${\mathrm{Al}}_{72}$ ${\mathrm{Si}}_6$ ${\mathrm{Mn}}_{22}$.