Optimizing the magnetocaloric response of FeCoNiMnxSi2-x high-entropy alloys through composition-driven critical phenomenon

The magnetocaloric effect (MCE) in high-entropy alloys (HEAs) is governed by a complex interplay of composition, electronic structure, and multi-channel entropy contributions. This study employs an integrated multiscale computational framework to decipher the role of the Mn/Si chemical ratio in tuning the magnetocaloric properties of FeCoNiMnxSi2-x(x = 0.9~1.25) HEAs. Special quasi-random structures confirm stable face-centered cubic solid solutions across all compositions. First-principles calculations reveal that the Curie temperature and magnetic moment are optimized at x = 1.1, driven by an upshifted Mn-3d band center and moderate Si-Mn p-d hybridization. Excessive Mn (x = 1.25) introduces competing antiferromagnetic coupling, degrading magnetic order. A key advance of this work is the microscopic decomposition of the total entropy change, which uncovers a substantial and tunable lattice contribution (≈15–20%), highlighting the significance of magneto-lattice coupling in HEAs—a feature often negligible in conventional counterparts. Critical exponent analysis confirms a second-order phase transition with composition-dependent scaling behavior. These results establish a causative chain from composition through electronic structure to magnetic interactions and multi-channel thermodynamics, providing a fundamental blueprint for the rational design of high-performance magnetocaloric HEAs.