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

Structural and magnetic phase transitions of Ni1.7Co0.3Mn1+xAl1−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 (|ΔSM|pk) of 2.1 J kg−1 K−1 and refrigerant capacity (RC) of 49 J kg−1 with ΔH = 10 kOe, originating from the martensitic transformation. The |ΔSM|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 |ΔSM|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.

► Ni1.7Co0.3Mn1+xAl1−x (x = 0.22–0.3) alloys were produced.
► Structural/magnetic phase transitions and magnetocaloric effect were characterized.
► The alloys exhibited large inverse MCE resulting from martensitic transformation.
► The alloy with x = 0.26 had the highest maximum entropy change at 10 kOe.