Effect of Cu substitution on magnetocaloric and critical behavior in Ni47Mn40Sn13−xCux alloys

A series of Heusler phases Ni47Mn40Sn13−xCux (x = 0, 0.5, 1, 1.25), which are magnetic shape-memory alloys, has been synthesized by mechanical alloying (MA) and characterized. The martensite-austenite phase transition was investigated by X-ray diffraction, differential scanning calorimetry, and DC magnetization measurements. With greater Cu content, the martensitic transition temperature TM increases while the magnetic transition temperature of austenite TcA remains almost unchanged. The maximum inverse magnetic entropy changes ΔSM for the x = 0.5 and x = 1 samples are nearly twice as high as for the undoped sample. Furthermore, the martensitic transformation of the doped samples occurs around room temperature, which is important for applications. Effective refrigerant capacities (RCeff) reduced due to the higher hysteresis losses in the x = 0.5 and x = 1 samples compare to the undoped one. Refrigerant capacities (RC) were examined in TcA. The largest value of RC = 207 J/kg was measured for the undoped sample. Critical properties near the ferromagnetic-paramagnetic (FM-PM) phase transition were analyzed in detailed. The critical parameters β, γ, δ and TcA of the x = 0 and x = 0.5 samples, which were determined through use of modified Arrott plots, the Kouvel-Fisher method, and the Widom scaling relation, differed from the mean-field values. The critical behavior indicates that long-range ferromagnetic order dominates in these Cu-doped samples.