Effect of Al doping on structural and magnetic properties of Ni₅₀Mn₃₇Al_xSb_13−x alloy

The Ni₅₀Mn₃₇Al_xSb_13−x (x=0, 1, 3 and 5) alloys were prepared by tri-arc melting technique. The replacement of Sb by Al increases the martensitic transformation temperature (T_M) as well as ferromagnetic to paramagnetic transformation temperature (T_C^A) within the austenite phase. The increase in T_M is found to due to the enhancement of hybridization between 3d states of Ni and Mn atoms. We also observed a large exchange bias field (H_EB) of 470 Oe for x=0 and it decreases with the Al concentration for field cooled (FC) magnetic hysteresis loop. A large magnetic entropy change (ΔS_M) of 10 J/kg-K is found for x=1 alloy under a field change (ΔH) of 50 kOe and it decreased for further higher concentration of Al doping. The possible reasons for observed behaviors are discussed