Curie Temperature Engineering in High Entropy Alloys for Magnetocaloric Applications

High entropy alloys (HEAs) are useful in applications that requir high strength, oxidation resistance, and high temperature stability. Research on HEAs for magnetocaloric applications focuses on increasing the refrigeration constant and controlling the Curie temperature (Tc). Here we investigate the effect of metal additions on exchange interaction distributions in eqiatomic ferromagnetic alloys of Fe, Co, and Ni. The metal additions are (a) noble metals (e.g., Cu, Ag), (b) antiferromagnetic transition metals (e.g., Mn), (c) Stoner-enhanced transition metals (e.g., Pt), and (d) early transition metals (e.g., Mo) that contribute to the virtual bound states. We are able to: 1) stabilize a ferromagnetic face-centered cubic γ-phase with equiatomic compositions in 4-, 5-, and 6-component systems, 2) make slight departures from equiatomic compositions to a chosen alloy to bring its Tccloser to room temperature, and 3) measure the role of alloying on exchange interaction distributions. We present a simple model to predict Tcin HEAs using the Bethe-Slater curve and binary phase diagrams of alloy constituents. Compared to the rare-earth-based magnetocaloric materials, the HEAs investigated here have significantly lower costs.