RKKY interaction and a pseudo-gap in terahertz conductivity spectra of the AuFe spin glass

Methods of terahertz BWT spectroscopy and optical ellipsometry in the range of frequencies from 0.3 THz to 1000 THz (10–33000 cm−1) at temperatures of 5–300 K were used for the first time to measure spectra of the electrodynamic response of a spin glass of composition Au-Fe (6 at % Fe). In the spin-glass state, at T < 100 K, dispersion of the dynamic conductivity has been discovered in the vicinity of a frequency of 0.5 THz, whose origin is ascribed to the appearance of a mobility gap in the subsystem of free electrons involved into RKKY interaction between the magnetic centers of Fe. It has been established that at 300 K the spectra of Au and AuFe have a shape typical of metals; the microscopic parameters of charge carriers, i.e., the relaxation frequency and plasma frequency, have been determined.