Shifting from Ising model to Heisenberg model critical behavior and the departure from these models in Fe73.5−Cr Cu1Nb3Si13.5B9

Abstract

Abstract The universality classes of amorphous alloy system Fe73.5−xCrxCu1Nb3Si13.5B9 with x = 0, 2, 4, 6, 8, and 10 are studied by determination of the static critical exponents (β, γ, δ), and critical temperatures from magnetization measurements using two independent methods, namely the Kouvel-Fisher method and the Berger-Campillo et al method. The found values for these critical exponents depend on the content of Cr and interestingly vary from values that correspond to universality classes of standard models (Ising (sample with x = 0), XY (sample with x = 2), and Heisenberg (sample with x = 4)) with short-range interactions to universality class of mean field model (samples with x = 6, 8, and 10) with long-range interactions. The critical temperature decreases quasi linearly with the increase of Cr content. The possible mechanisms leading to such universality classes and shift including the spin-orbit interaction, shape anisotropies, direct exchange and itinerant exchange are analyzed. In addition, X-ray diffraction and Mossbauer spectroscopy studies performed on this alloy system reveal that it has a heterogeneous structure.