Phase transitions and magnetocaloric effect of Ni1.7Co0.3Mn1+xAl1−x Heusler alloys

Abstract Structural and magnetic phase transitions of Ni 1.7 Co 0.3 Mn 1+ x Al 1− x ( x  = 0.22–0.3) alloys were characterized to evaluate the magnetocaloric effect (MCE) of the alloys. The Curie temperature remained at ∼360 K regardless of the composition whereas the Al fraction determined the temperature and extent of the martensitic transition. The alloy with x  = 0.26 had the highest peak magnetic entropy change (|Δ S M | pk ) of 2.1 J kg −1  K −1 and refrigerant capacity (RC) of 49 J kg −1 with Δ H  = 10 kOe, originating from the martensitic transformation. The |Δ S M | pk and RC values were comparable to those of other Ni–Mn– X alloys. The alloy with x  = 0.3 may also serve as a magnetic refrigerant near room temperature in spite of its relatively low |Δ S M | pk and RC values. Our result suggests that it should be possible to fine-tune the composition of the quaternary NiCoMnAl alloy to attain optimal magnetocaloric effect near room temperature.