Microstructure, martensitic transitions, magnetocaloric, and exchange bias properties in Fe-doped Ni-Mn-Sn melt-spun ribbons

Abstract

The effects of Fe substitution for Ni on microstructure, phase transformations, magnetocaloric effect, and exchange-bias behavior of the Ni46−xFexMn43Sn11 (x = 0–3) alloy ribbons have been investigated. The free surface of as-spun Fe-doped ribbons shows the granular microstructure containing multiple shapes (the tree leaf-like, small columnar grain, etc.), while the ordered columnar grains are observed in fracture cross-section. The martensitic structural transition temperature (TM) of as-annealed ribbons decreases from 240 K for x = 0 to 185 K for x = 3 due to the decrease in valence electron concentration, while the Curie temperature of the austenitic phase remains almost unchanged (TC = 275 K). The positive values of magnetic entropy changes (+ΔSM), around TM, are 21.0, 29.1, 24.1, and 14.8 J/kg K for x = 0–3, respectively, while the negative −ΔSM values vary in 3.0–3.5 J/kg K range around TC, under a field change of 0–5 T. The values of exchange-bias field (HE) at 10 K change in the range of 469 to 534 Oe and the coercivity (HC) slightly decreases from 245 to 186 Oe, respectively, as x is increased.