Martensitic transformation and magnetic characteristics in Ni50Mn36Sn14-xBix Heusler alloys

The addition of the fourth element has a prominent effect on the magnetic characteristics in Ni-Mn based Heusler alloys. In this work, we have systematically investigated the magnetocaloric effect, martensitic transformation, and exchange bias properties of Ni50Mn36Sn14-xBix (x = 0, 0.2, 0.4 and 0.6) Heusler alloys produced by arc melting technique. The XRD analysis demonstrates that all samples stabilize with L2(1) cubic structure at room temperature. The region of martensitic transformation shifts rapidly towards higher temperature (increasing martensitic transformation start temperature from 245 to 284 K). The appearance of magnetic transformation of martensite phase leads to the great difference of magnetization between martensite and austenite states. Associated with field-induced reverse martensitic transformation, an inverse magnetocaloric effect was observed in the Bi-doped alloys. The Maxwell relation was employed for determining the magnetic entropy change (increment S-M), and a sizeable positive increment S-M of 33.3 J/kg.K was achieved for Ni50Mn36Sn13.6Bi0.4 alloy, which is more than twice as high as the parent alloy (similar to 14.3 J/kg.K). In addition, the magnetic hysteresis loops at low temperature unveil the fact that the EB effect is discerned for all studied alloys. The exchange bias field (H-E) increases from 280.5 to 352.5 Oe by Bi doping after 500 Oe field cooling. Our findings furnish a reference for the selection of less costly magnetocaloric materials.