Investigation of critical phenomena and magnetocaloric effect (MCE) in amorphous Tb₈₀Au₂₀ foils

Abstract

This work investigates the magnetic critical behavior and magnetocaloric effect (MCE) of an amorphous Tb₈₀Au₂₀ alloy. Rare-earth–based amorphous systems are of interest both for their unusual magnetic properties and their potential in energy-efficient cooling technologies. Magnetization measurements reveal a second-order transition from the ferromagnetic to the paramagnetic state at a Curie temperature of about 70 K. To characterize this transition, we determined the critical exponents (β, γ, δ, and n) using several complementary techniques: Modified Arrott plots (MAP), Kouvel–Fisher analysis (K-F), critical isotherm method (CIA), and Widom scaling relation (WSR): β = 0.395, γ = 1.064, δ = 3.03, and n ≈ 0.78. The values obtained are consistent across these approaches and closely follow the predictions of the mean-field model, indicating that long-range ferromagnetic interactions dominate in this amorphous compound. The magnetocaloric properties were also examined to validate the critical behavior. The alloy exhibits a maximum magnetic entropy change of approximately 2.30 J kg⁻¹ K⁻¹ and a relative cooling power of about 322 J kg⁻¹ under an applied field change of 0–4.5 T The broad temperature span of the entropy change, combined with the absence of thermal and magnetic hysteresis, confirms the advantages of second-order transitions. These findings highlight the potential of Tb-based amorphous alloys as promising candidates for cryogenic magnetic refrigeration.