文摘

In this work, we present a detailed study of the magnetic properties and the magnetocaloric effect at room temperature of Ni50?em class="a-plus-plus">x Ag x Mn37Sn13 alloys with x = 1, 2, and 4, which were prepared by using an arc-melting method. Experimental results reveal that a partial replacement of Ag for Ni leads to a decrease in the anti-FM phase in the alloys. In addition, the martensitic-austenitic phase transition shifts towards lower temperature and is broaded. The Curie temperature (T C A ) for the austenitic phase also shifts toward to lower temperature, but not by much. The Curie temperature was found to be 308, 305, and 298 K for x = 1, 2, and 4, respectively. The magnetic entropy change (ΔS m ) of the samples was calculated by using isothermal magnetization data. Under an applied magnetic field change of 10 kOe, the maximum value of ΔS m (|ΔS max |) was achieved at around room temperature and did not change much (~0.8 J·kg?·K?) with increasing Ag-doping concentration. Particularly, the M 2 vs. H/M curves prove that all the samples exhibited a second-order magnetic phase transition. Based on Landau’s phase-transition theory and careful analyses of the magnetic data around the T C A , we have determined the critical parameters β, γ, δ, and T C . The results show that the β values are located between those expected for the 3D-Heisenberg model (β = 0.365) and mean-field theory (β = 0.5). Such a result proves the coexistence of short-range and long-range ferromagnetic interactions in Ni50?em class="a-plus-plus">x Ag x Mn37Sn13 alloys. The nature of the changes in the critical parameters and the |ΔS max | is thoroughly discussed by means of structural analyses.