Scaling of Nonlinear Susceptibility in MnCu and GdAl Spin-Glasses

SQUID measurements of susceptibility χ versus field H are fitted by χ=χ₀-χ₁H^a-1 at a given temperature T, for two classic spin-glasses: 4.6% Mn in Cu (polycrystalline) and 37% Gd in Al (amorphous). χ₁(T) shows a much stronger anomaly than χ₀(T), while $a(T)$ has a minimum at the freezing temperature Tf. The data can also be scaled according to χ₀-χ=H^2δf((T-Tf)H^2φ) with δ=5±1 and φ=4.5±0.5.