Magnetocaloric Effect in $\hbox {Ni}_{0.5}\hbox {Mn}_{0.5-{\rm x}}\hbox {Sn}_{\rm x}$ Alloys

We have studied the magnetic properties and magnetocaloric effect in bulk Ni_0.5Mn_0.5-xSn_x alloys (x = 0.2 and 0.3) prepared by arc-melting. Experimental results reveal that with increasing Sn content the ferromagnetic order slightly decreases, but the Curie temperature (T_C) increases from 333 K (for x = 0.2) to about 354 K (for x - 0.3). Based on magnetic-field dependences of magnetization (M - H curves) recorded at various temperatures, ΔS_M (T) curves of the samples under an applied field interval of 0-12.0 kOe were obtained. Maximum ΔS_M values achieved around T_C are about 1.2 and 1.1 J.kg^-1.K^-1 for x = 0.2 and 0.3, respectively. Detailed analyses of M - H curves in the vicinity of T_C, used the Arrott-Noakes method, reveal the samples undergoing the second-order phase transition with the critical exponents of β = 0.503 ± 0.021 and γ = 1.246 ± 0.013 for x = 0.2, and of β = 0.426 ± 0.016 and 7 = 1.232 ± 0.014 for x = 0.3. The difference in value of the exponents together with x-ray diffraction data will be used to explain the magnetic properties and magnetocaloric effect in Ni_0.5Mn_0.5-xSn_x.