Effect of Co addition on the martensitic transformation and magnetocaloric effect of Ni–Mn–Al ferromagnetic shape memory alloys

• Magnetic and magnetocaloric properties of Ni50−xCoxMn32Al18 alloys are reported.
• A ferromagnetic to weak-magnetic martensitic transition is observed.
• The magnetic phase diagram of Ni50−xCoxMn32Al18 alloys was established.
• Ferromagnetic coupling is significantly enhanced by doping the Co elements.
• The maximum ΔSM is 7.7 J/kg K at 60 kOe for the composition x = 8.

A series of Ni50−xCoxMn32Al18 (x = 3, 4, 5, 6, 7, and 8) alloys were prepared by the arc melting method. The martensitic transformation (MT) shifts to a lower temperature with increasing Co concentration and can be tuned to occur from a ferromagnetic austenite to a weak-magnetic martensite in the range of 6 ≤ x ≤ 8. The field-induced metamagnetic behavior was realized in Ni42Co8Mn32Al18 sample in which a large magnetic entropy change of 7.7 J/kg K and an effective refrigerant capacity value of 112 J/kg were obtained under the field of 60 kOe. The large magnetocaloric effect and adjustable MT temperature suggest that Ni–Co–Mn–Al alloys should have promising potential as magnetic refrigerants.