Unusual Dynamical Properties of Self-Interstitials Trapped at Co Impurities in Al

Abstract

M\"ossbauer spectroscopy was used to study the dynamics of Al self-interstitials trapped at $^{57}\mathrm{Co}$ impurities. When a single interstitial atom is trapped at the $^{57}\mathrm{Co}$ atom, the Debye-Waller factor decreases rapidly by more than a factor 4 in the temperature interval between 13 and 20 K. We try to explain this anomaly by the following model: The $^{57}\mathrm{Co}$ atom jumps between six different positions, thereby forming mixed Co-Al dumbbells with changing Al partners.