Martensitic Transformation and Magnetic Properties of Ni-Co-Mn-In-Gd Ferromagnetic Shape Memory Alloys

The effect of rare earth Gd on the microstructure, martensitic transformation and magnetic properties of Ni45Co5Mn35In15-xGdx (0 <= x <= 1.6 1.6) alloys is investigated. The addition of Gd results in a change in the microstructure. With the increase of Gd content, the grain size is clearly reduced and the volume fraction of the second phase increases gradually. And then the second phase along the grain boundaries grows and connects to each other. Some disperse in the grains. One-step thermoelastic martensitic transformation is observed in Ni45Co5Mn35In15-xGdx alloys. When the Gd content reaches 0.8 (at%), the martensite transformation temperature decreases first, and then rises with the increase of Gd content. The near-room-temperature magnetocaloric effect (MCE) in polycrystalline Ni45Co5Mn35In14.2Gd0.8 alloys is observed. The magnetic-field-induced inverse phase transformation from martensite to austenite phase is confirmed. The inverse magnetic entropy change (Delta S-M) reaches 17.78 J/kg K for Ni45Co5Mn35In14.2Gd0.8 alloy at 277 K and its R-c is about 356 J Kg(-1) at an applied field of 5 T.