“…Using this definition of T*, which depends on concentration x, T* does not vary significantly between Tb-Si and Gd-Si, contrary to our own suggestion in the earliest work on this subject. 1 By contrast, preliminary measurements on amorphous Gd-Ge alloys suggest a strong dependence of T* on the semiconductor. 17 To summarize, we have shown that ͑1͒ the characteristic temperature below which the conductivity is strongly affected by the local moments does not appear to depend strongly on magnetic ion ͑Tb vs Gd͒, ͑2͒ the effective moment p e f f in the amorphous Tb-Si system shows the same dependence on composition as it did in the amorphous Gd-Si system, with a strong peak at the M-I transition and significant suppression below the expected Tb 3ϩ value for both metallic and insulating samples, ͑3͒ the strengths of exchange interactions are comparable for amorphous Tb-Si and amorphous Gd-Si, in contrast to the different de Gennes factor, but are still nearly perfectly balanced ferromagnetic and antiferromagnetic, and ͑4͒ the random anisotropy of the L ϭ0 Tb ion has a strong effect on the magnetic freezing, causing a poorly defined and strongly frequency-dependent transition more reminiscent of a blocking temperature than the spin-glass freezing seen in amorphous Gd-Si.…”