Effect of Co substitution on the martensitic transformation and magnetocaloric properties of Ni₅₀Mn_35−xCo_xSn₁₅

Abstract

Martensitic transformation and magnetic entropy change in Co substituted Ni 50 Mn 35−x Co x Sn 15 (x = 0, 1.0, 1.5, 2.0, and 3.0) Heusler alloys have been investigated by X-ray powder diffraction analysis, differential scanning calorimetry, and magnetic measurements. X-ray diffraction analysis reveals that the Ni 50 Mn 35−x Co x Sn 15 alloys have L2 1 Heusler structure at room temperature. The phase decomposition of the sample with x = 3.0, after annealing 48 h at 1173 K, is confirmed by both Xray powder diffraction analysis and energy-dispersive x-ray spectroscopy in scanning electron microscopy. With the increase of the Co content from 0 to 2.0, the martensitic transformation temperature T M increases from 185 to 245 K, which is in good agreement with the rule of valence electron concentration e/a-dependence of T M . The magnetic entropy change ΔS M is investigated in the vicinity of the martensitic transformation.