Magnetic properties and magnetic entropy change in Heusler alloys Ni ₅₀Mn_35-x Cu _x Sn₁₅

The influence of Cu substitution for Mn on magnetic properties and magnetic entropy change has been investigated in Heusler alloys, Ni₅₀Mn _35-x Cu _x Sn₁₅ (x=2,5 and 10). With increasing Cu content from x=2 to x=5, the martensitic transition temperature, T _M , decreases from 220 K to 120 K. Further increasing Cu up to x=10 results in the disappearance of T _M . For samples Ni ₅₀Mn₃₃Cu₂Sn₁₅ and Ni ₅₀Mn₃₀Cu₅Sn₁₅, both martensitic and austenitic states exhibit ferromagnetic characteristics, but the magnetization of martensitic phase is notably lower than that of austenitic phase. The magnetization difference, ΔM, across the martensitic transition leads to a considerably large Zeeman energy, μ ₀ΔṀH, which drives a field-induced metamagnetic transition. Associated with the metamagnetic behavior, a large positive magnetic entropy change ΔS takes place around T _M . For the sample Ni₅₀Mn₃₃Cu ₂Sn₁₅,ΔS reaches 13.5 J/kġ under a magnetic field change from 0 to 5 T.