Spectroscopy of metallic spin glasses.

We have measured the a.c. non-linear susceptibilities x(3)', x(5)' and x(7)' of very dilute AgMn spin glasses above and below the transition temperature T(g) as a function of frequency, temperature and magnetic field. In the static limit, these quantities display well defined critical singularities at T (g). The non-linear susceptibilities scale above T(g) as powers of frequency with weakly temperature dependent exponents. While the effective exponents satisfy the relations imposed by static and dynamic scaling, the observed temperature and frequency roundings suggests the presence of additional length scales.