Tailoring Si/Mn ratio to optimize magnetocaloric performance of FeCoNi-based high-entropy alloys

Abstract

This study systematically investigates the influence of the Si/Mn ratio on the magnetocaloric properties of FeCoNiSi_xMn_0.4-x (x = 0.1, 0.2, and 0.3) high-entropy alloys (HEAs) using a multi-scale computational approach. By combining special quasi-random structure (SQS) modeling, first-principles density functional theory (DFT) calculations, and atomic-scale magnetic simulations, we elucidate the synergistic effects of compositional disorder on the electronic structure and magnetic ordering. Key results indicate that increasing the Si content reduces the cell volume via atomic size effects and decreases the total magnetic moment, while significantly raising the Curie temperature (599–673 K) due to enhanced ferromagnetic exchange coupling. Under an applied field of 5 T, an optimized magnetocaloric response is observed: at x = 0.3, the magnetic entropy change exhibits a full width at half maximum of 2.61 J/(kg·K) along with a high relative cooling power (RCP = 515 J/kg), while a peak temperature-averaged entropy change (TEC) of 3.17 J/(kg·K) is achieved at x = 0.2 over a temperature span of 10 K (ΔT_H-C = 10 K). The maximum half-peak width of the magnetic entropy change (δT_FWHM) for this alloy system ranges from 156.0 K to 196.1 K. This work reveals an underlying composition–electronic–magnetic correlation mechanism, suggesting promising potential for designing high-temperature solid-state refrigeration materials with broad operational windows.