Enhanced refrigerant capacity and Curie temperature of amorphous Gd₆₀Fe₂₀Al₂₀ microwires

Gd₆₀Fe₂₀Al₂₀ microwires with an average diameter of ∼44 μm were fabricated by the melt-extraction method. XRD, TEM and HRTEM confirmed the amorphous nature of the microwires. The dimensional and chemical uniformity of the microwires over their length were confirmed by SEM and EDS, respectively. Magnetization measurements revealed a broad paramagnetic to ferromagnetic phase transition at T_C ∼202 K. For μ₀ΔH = 5 T, the microwires exhibit a broad magnetic entropy change with its maximum value ΔS_M^max of ∼4.8 J kg⁻¹ K⁻¹ and a large refrigerant capacity (RC) of ∼687 J kg⁻¹ over a large temperature interval (150 K). This RC value of the microwires is larger than those of the previously reported bulk and ribbon counterparts. An analysis of critical exponents reveals that γ = 1.246 ± 0.017 is close to that predicted by the 3D Ising theoretical model, while β = 0.723 ± 0.011 does not agree with any of the critical exponents predicted by the existing models. This can be attributed to the antiferromagnetic coupling between the rare earth (Gd) and the transition metal (Fe). The origins of the broad magnetic phase transition, the broad magnetic entropy change, and the large refrigerant capacity are discussed.