Dynamic Evidence for a Transition at T c = 0 in the Ising Anisotropic Spin Glass Fe 0.3 Mg 0.7 Cl ₂

We present the results of a dynamic study of the susceptibility in the Ising anisotropic spin-glass Fe0.3Mg0.7Cl2using Faraday rotation in the (1.5 ÷ 80 000) Hz range. The variation of the relaxation time at low temperature can be fitted either by a power law with a diverging exponent or by an Arrhenius law. It is shown explicitly that both laws, in fact, mean the same result which is the natural expectation of usual scaling theory in the limit when Tc→ 0.