Static critical exponents of the ferromagnetic transition in spin glass re-entrant systems

The static critical phenomenology near the Curie temperature of the re-entrant metallic alloys Au0.81Fe0.19, Ni0.78Mn0.22, Ni0.79Mn0.21 and amorphous a-Fe0.98Zr0.08 is studied using a variety of experimental techniques and methods of analysis. We have generally found that the values for the exponents α, β, γ and δ depart significantly from the predictions for the 3D Heisenberg model and are intermediate between these expectations and the values characterizing a typical spin glass transition. Comparing the exponents obtained in our work with indices for other re-entrant systems reported in the literature, a weak universality class may be defined where the exponents are distributed within a certain range around average values