Johari–Goldstein relaxation as the origin of the excess wing observed in metallic glasses

Measurements of the shear loss modulus G″ of amorphous Zr65Al7.5Cu27.5 at 5.4 kHz were reported by Rösner, Samwer and Lunkenheimer. They observed that the measured G″ are in excess of the contribution from the α-relaxation, indicating the existence of an ‘excess wing’ in amorphous metals like that found in molecular glass-formers. They speculated that the excess wing found in amorphous metal is due to the presence of an unresolved Johari–Goldstein (JG) secondary relaxation. In this work, the coupling model is used to calculate the temperature TJG at which the JG relaxation frequency coincides with the experimental frequency of the isochronal measurement. The location of TJG is well within the temperature range where the excess wing of Zr65Al7.5Cu27.5 appears at 5.4 kHz. Hence, the result supports the assertion of Rösner et al. that the excess wing found in the metallic glass originates from the intrinsic JG relaxation.