On the magnetocaloric effect in biphasic FeCrSiB amorphous composites

Abstract

Room-temperature magnetic refrigeration using the Ericsson cycle relies on materials with a large, nearly constant magnetocaloric (MC) effect over a wide temperature range. Here, we examine the MC properties of biphasic composite systems made from Fe–Cr–Si–B amorphous alloys. The precursor compositions, Fe_68.8Cr_11.2Si₆B₁₄ and Fe_70.4Cr_9.6Si₆B₁₄, show a second-order magnetic phase transition with values of the Curie temperature (TC) close to 290 K and 340 K, respectively. Analysis of critical exponents reveals that both alloys display intermediate critical behavior, between mean-field and three-dimensional Heisenberg universality classes. Guided by the individual isothermal magnetic entropy change versus temperature curves, we have designed a composite by combining the two alloys in proportions that yield a nearly constant entropy change, achieving |ΔS_comp| ≈ 1.8 J kg^-1 K^-1 for a magnetic field change of µ₀ΔH = 5 T. This table-like behavior persists over a temperature range of about 50 K, as determined by the TC values of the parent alloys. We also assessed the effective refrigerant capacity (RC_eff) and temperature-averaged entropy change (TEC) for the composite. The customized MC response delivers a competitive RC_eff (87 J kg^-1 at µ₀ΔH = 5 T) and a TEC that is almost independent of the operating temperature range. This shows that rational design of Fe- based amorphous composites provides an adaptable solution for Ericsson-cycle magnetic refrigeration by balancing performance, operating temperature, and material cost.