Al27 NMR local study of the Al0.5TiZrPdCuNi alloy in high-entropy alloy and metallic glass forms

Abstract

We report a $^{27}\mathrm{Al}$ nuclear magnetic resonance (NMR) local spectroscopic study of the NMR lineshape and Knight shift of a six-component ${\mathrm{Al}}_{0.5}\mathrm{TiZrPdCuNi}$ metallic alloy that can be prepared either as a crystalline high-entropy alloy (HEA) or as an amorphous metallic glass (MG) at the same chemical composition. For both structural modifications of the material (HEA and MG), we have determined the distribution of electric-field-gradient (EFG) tensors and the local electronic density of states (DOS) $g({\ensuremath{\varepsilon}}_{\mathrm{F}})$ at the Fermi level at the position of $^{27}\mathrm{Al}$ nuclei. A theoretical $I=\frac{5}{2}$ quadrupole-perturbed NMR spectrum, pertinent to both cubic HEAs and amorphous MGs, has been derived using the Gaussian isotropic model of the EFG tensor distribution, and excellent fits of the experimental spectra were obtained. The EFG distribution function of the MG state is about twice broader than that of the HEA state, reflecting the existence of a (distorted) crystal lattice in the latter and its absence in the former. The ${T}^{2}$ dependence of the Knight shift indicates that the DOS is changing rapidly with energy within the Fermi level region for both structural modifications. The local DOS at the $^{27}\mathrm{Al}$ sites of the HEA sample is $\ensuremath{\sim}10%$ larger than that of the MG state, indicating comparable degrees of disorder.