The Effect of B Doping on the Martensitic Transitions, Magnetocaloric and Magnetic Properties in Ni $_{48}$ Mn

The influence of boron substitution for indium on phase transformation, magnetocaloric and exchange bias (EB) properties in annealed Ni₄₈Mn₃₉In_13-xB_x (x = 1-4) ribbons has been investigated. It is observed that an increase in B concentration strongly affects the magnetic state of the martensitic phase, the magnetic entropy change and the EB properties of the ribbons. These ribbons crystallize in a partially ordered B2 phase structure. The martensitic structural transition temperature (T_M) decreases from 270 K for x = 0 to 175 K for x = 2 with increasing B content. A further increase in B content results in an increase of T_M to 268 K for x = 4. The peak value of positive magnetic entropy change (ΔS_M) decreases from 20.2 J/kg K for x = 0 to 2.8 J/kg K for x = 4 for a magnetic field change H = 50 kOe. The values of exchange bias field (H_E) and the coercivity (H_C) change from 258 Oe and 192 Oe to 397 Oe and 600 Oe, respectively, as x is increased from 0 to 4. The phenomena are attributed to the change of exchange interactions in B-substituted Ni-Mn-In ribbons due to the change of distance between Mn atoms.