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

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 (T-M) of as-annealed ribbons decreases from 240K for x = 0 to 185K for x = 3 due to the decrease in valence electron concentration, while the Curie temperature of the austenitic phase remains almost unchanged (T-C = 275 K). The positive values of magnetic entropy changes (+Delta S-M), around T-M, are 21.0, 29.1, 24.1, and 14.8 J/kg K for x = 0-3, respectively, while the negative -Delta S-M values vary in 3.0-3.5 J/kg K range around T-C, under a field change of 0-5T. The values of exchange-bias field (H-E) at 10K change in the range of 469 to 534 Oe and the coercivity (H-C) slightly decreases from 245 to 186 Oe, respectively, as x is increased. (C) 2013 American Institute of Physics.