Enhanced Magnetocaloric Properties of the (MnNi)Si(FeCo)Ge High-Entropy Alloy Obtained by Co Substitution.

In order to improve the magnetocaloric properties of MnNiSi-based alloys, a new type of high-entropy magnetocaloric alloy was constructed. In this work, MnNiSiFeCoGe ( = 0.4, 0.45, and 0.5) are found to exhibit magnetostructural first-order phase transitions from high-temperature NiIn-type phases to low-temperature TiNiSi-type phases so that the alloys can achieve giant magnetocaloric effects. We investigate why / (/) gradually increases upon Co substitution, while phase transition temperature () and isothermal magnetic entropy change (Δ) tend to gradually decrease. In particular, the = 0.4 alloy with remarkable magnetocaloric properties is obtained by tuning Co/Ni, which shows a giant entropy change of 48.5 J∙kgK at 309 K for 5 T and an adiabatic temperature change (Δ) of 8.6 K at 306.5 K. Moreover, the = 0.55 HEA shows great hardness and compressive strength with values of 552 HV2 and 267 MPa, respectively, indicating that the mechanical properties undergo an effective enhancement. The large Δ and Δ may enable the MnNiSi-based HEAs to become a potential commercialized magnetocaloric material.