Phase Transition and Magnetocaloric Properties of Ni50Mn35–xIn15Cux Bulk Alloys and Ribbons

The martensitic and magnetic phase transitions are investigated in Ni₅₀Mn_35-xIn₁₅Cu_x (x = 0, 1, 2, 3, 4, and 5) ferromagnetic shape memory alloys using X-ray diffraction, differential thermal analysis, and magnetization measurements. Ascribed to the increase of valence electron concentration, the martensitic transformation temperatures increase to over room temperature with the increase of Cu-substitution, both in bulks and ribbons. Curie temperature of martensitic phase, however, decreases with Cu-substitution. Thermomagnetic curves show that the magnetic and structural transitions are coupled from x = 0 to 3. Cu-substitution improves magnetocaloric effect (MCE). The comparison between bulks and ribbons shows that the martensitic transformation temperatures and the MCE of ribbons are slightly lower than those of the bulks, and are suggested to be related to Mn-volatilization in annealed bulks, small and inhomogeneous grain sizes in ribbons.