Magnetic properties and magnetocaloric effect at room temperature of Ni50-xAgxMn37Sn13 alloys

In this work, we present a detailed study of the magnetic properties and the magnetocaloric effect at room temperature of Ni50-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 (Delta S (m) ) of the samples was calculated by using isothermal magnetization data. Under an applied magnetic field change of 10 kOe, the maximum value of Delta S (m) (|Delta S (max) |) was achieved at around room temperature and did not change much (similar to 0.8 J center dot kg(-1)center dot K-1) 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 beta, gamma, delta, and T (C) . The results show that the beta values are located between those expected for the 3D-Heisenberg model (beta = 0.365) and mean-field theory (beta = 0.5). Such a result proves the coexistence of short-range and long-range ferromagnetic interactions in Ni50-x Ag (x) Mn37Sn13 alloys. The nature of the changes in the critical parameters and the |Delta S (max) | is thoroughly discussed by means of structural analyses.