Annealing Effect on Martensitic Transformation and Magneto-Structural Properties of Ni-Mn-In Melt Spun Ribbons

摘要

We report the effect of a short-time vacuum annealing (1073 K during 10 minutes) on structural phase transition temperatures and magneto-structural properties of as-quenched ribbons of the Heusler alloy Ni_(50.6)Mn_(34.5)In_(14.9). This alloy crystallizes in a single phase cubic B2-type austenite with a Curie point of T_C~A=284 K that with the lowering in temperature transforms into a martensite with T_C~M≈185 K. The direct and reverse martensitic phase transition temperatures were M_S=251 K, M_f= 221 K, A_s = 239 K, and A_f= 266 K. After annealing austenite shows the highly ordered L2_1-type structure while the average chemical composition as well as the structural and magnetic transition temperatures were shifted to Ni_(50.2)Mn_(34.3)In_(15.5) and M_S = 253 K, M_f= 238 K, A_s = 257 K, A_f= 265 K, ΔT = 13 K, T_C~A = 299 K and T_C~M≈207 K. In the annealed samples the magnetization changes associated to the magnetic and structural transitions are more abrupt and magnetization isotherms in both the austenitic and martensitic existence region show higher initial magnetic susceptibility and faster approach to saturation. Field-cooled hysteresis loops at 10 K were shifted along the negative H-axis for both samples, but a significant anomaly was evident on the left side of the hysteresis loop for as-quenched ribbons.