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 similar to 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 (vertical bar Delta S-M vertical bar(pk)) of 2.1 J kg(-1) K-1 and refrigerant capacity (RC) of 49 J kg(-1) with Delta H = 10 kOe, originating from the martensitic transformation. The vertical bar Delta S-M vertical bar(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 vertical bar Delta S-M vertical bar(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. (c) 2013 Elsevier B.V. All rights reserved.