Martensitic Transitions and Magnetocaloric Properties in Mn49–xCoxNi41Sn10 ( –4) Rib

The effects of Co substitution for Mn on the phase constitutions, martensitic transition temperature TM, and the magnetocaloric properties of melt-spun Mn_49-xCo_xNi₄₁Sn₁₀ (x = 0-4) alloy ribbons have been investigated. A unique martensitic transformation (MT) from a ferromagnetic (FM) austenite to a weak-magnetic martensite phase was obtained, and magneticfield-induced reverse MT was confirmed in these ribbons. These ribbons crystallize in a cubic Heusler structure (L2₁) at room temperature. The martensitic structural transition temperature (TM) first decreases from 239.7 K for x = 0 to 237.5 K for x = 1.5 with increasing Co content. A further increase of Co content results in an increase to 251.6 K for x = 4. The peak value of positive magnetic entropy change (ASM) first decreases from 15.8 Jkg/K for x = 0 to 9.9 Jkg/K for x = 1.5, then increases to 11.5 for x = 4 in a magnetic field change 10 kOe. The phenomena are attributed to the change of exchange interactions in Co-substituted Mn-Ni-Sn ribbons due to the change of the FM behavior and the valence electron concentration electrons per atom.