Magnetic Properties and Large Magnetocaloric Effect in Amorphous Fe-Ag-Ni-Zr for Room-Temperature Magnetic Refrigeration

This paper reveals that a partial replacement of Fe by Ni (5%) and/or Ag (2%) in amorphous Fe_85-xAg_xNi₅Zr₁₀ (x = 0 and 2) alloys leads to the shift of T toward room temperature (RT) (T_C = 308 and 303 K for x = 0 and 2, respectively). Basing on isothermal magnetization data, the magnetic entropy change (ΔS_m) of the amorphous alloys was calculated. Their maximum ΔS_m values (|ΔS_max|) achieve just around RT, corresponding to the ferromagnetic-paramagnetic (FM-PM) phase transition of the amorphous phase. Under a magnetic field change of 10 kOe, |ΔS_max| values are ~1 J · kg^-1 · K^-1. We have also used different methods, such as the modified Arrott plots, the Kouvel-Fisher method, and critical isotherm analysis to study their critical property around the FM-PM phase transition. Our results suggest that the amorphous Fe_85-xAg_xNi₅Zr₁₀ alloys exhibit a second-order magnetic phase transition with the critical exponents of β = 0.389-0.396 and y = 1.279-1.334 close to those expected for the 3-D Heisenberg model. This proves the existence of short-range FM interactions in these alloys.