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In search of low-cost, hysteresis-free, broad working temperature magnetocaloric materials, Ni_2.24Mn_0.76Sn Heusler alloy has been prepared by the conventional arc melting method. The XRD pattern reveals that the sample is crystallized in Fm m space group in L2₁ cubic symmetry. The Maxwell's equation is employed on magnetic isotherms to determine the change in magnetic entropy. This alloy gives a reasonable magnetocaloric effect ( = 1.25 J/Kg-K and RCP = 83.87 J/Kg at 3 T) with a large working temperature (67 K at 3 T) near the room temperature. Critical exponents have been calculated using modified Arrott plot, Kouvel–Fisher plot, and critical isotherm analysis to understand the nature of phase transition and exchange interaction, causing magnetic ordering in the system. The values of critical exponents (β = 0.454 ± 0.015, γ = 1.145 ± 0.035, δ = 3.522 ± 0.009) and …