Magnetic phase transitions in spin glasses

The nature of a phase transition in spin glasses remains unsettled. Its characterization lies in experimentation on materials which closely mimic the theoretical models. Here I consider the 'ideal' (2D-Ising) spin glass Rb2Cu1-xCoxF4. The complex ac-susceptibility is measured as a function of temperature and frequency. The results are analyzed to determine the median relaxation time which diverges towards Tc = 0 K according to activated dynamics. Far above Tc the relaxation time leaves the experimentally available window. Consequently an equilibrium phase transition cannot be studied as T &rarr Tc+. A similar situation is expected for model 3D spin glasses where Tc is finite.