A less expensive NiMnGa based Heusler alloy for magnetic refrigeration

We present a study of the substitution of Mn by Cu on the compound N i 2 M n 1 - x C u x G a 0 . 9 A l 0 . 1 , showing that the substitution of a small amount of Al on the Ga site does not affect the magnetic and magnetocaloric potential compared to N i 2 (Mn,Cu)Ga alloy. The samples were prepared with 10% substitution of Al and with Cu concentrations of x =0.0, 0.2, and 0.3. Magnetization measurements as a function of temperature performed from 10 to 400 K, with an applied field of 0.02 T showed a ferromagnetic state, with critical temperature T c =295 and 300 K for the samples with Cu, x =0.2 and 0.3, respectively. For the sample without Cu, a complex behavior is observed at T c =370 K, with martensitic transition at 220 K and a premartensitic at 250 K. Analysis of x-rays diffractograms at room temperature show a L 2 1 structure for x =0.0, while for x =0.2 a mixture of L 2 1 and martensitic is present, and the sample with x =0.3 it is in a fully martensitic phase. Heat capacity measurements were performed in order to calculate magnetocaloric effect in the samples. The results indicate that in Ni(Mn,Cu)Ga alloys, a partial substitution of Ga by Al still produce a high refrigerant capacity while reducing the costs of fabrication.