The inverse magnetocaloric effect (IMCE) in ferromagnetic Ni-Mn-Sn alloys is reported, where applying a magnetic field adiabatically causes cooling, unlike the conventional magnetocaloric effect (MCE) where removing the field leads to cooling. This inverse effect is observed in some intermetallic compounds, where a moderate entropy increase occurs upon field application. In Ni-Mn-Sn alloys, the entropy change is as large as that of giant MCE materials but with opposite sign, originating from martensitic phase transformations that modify magnetic exchange interactions. The MCE is a temperature change upon adiabatic magnetic field application, leading to spin reordering and cooling. Recent discoveries of giant MCE materials at room temperature have enabled room-temperature refrigeration. The MCE is largest near magnetic transition temperatures, where structural and magnetic phase transitions occur. In Ni-Mn-Sn alloys, the inverse MCE is observed, with entropy changes up to 18 J K⁻¹ kg⁻¹ for x = 0.13 and 15 J K⁻¹ kg⁻¹ for x = 0.15. This effect is due to the coupling between martensitic and magnetic domains, leading to magnetically inhomogeneous states. The Ni-Mn-Sn alloys exhibit structural and magnetic phase transformations, with inverse MCE three times larger than in other materials. The magnetocaloric properties are studied through magnetisation measurements, showing step-like behavior in magnetisation curves. The entropy change is calculated using the relationship ΔS(T,H) = μ₀ ∫₀ᴴ (∂M/∂T)ₕ dH. The results show positive entropy changes in the temperature range M_f < T < M_s, with maximum values of about 18 J K⁻¹ kg⁻¹ for x = 0.13. The inverse MCE in Ni-Mn-Sn alloys is significant, with entropy changes comparable to giant MCE materials. It is the largest observed so far for the inverse MCE and could be used for room-temperature refrigeration. The effect is attributed to the martensitic transition modifying magnetic properties, and the inverse MCE could be used as a heat sink in combination with conventional MCE materials. The study highlights the potential of Ni-Mn-Sn alloys for magnetic refrigeration applications.The inverse magnetocaloric effect (IMCE) in ferromagnetic Ni-Mn-Sn alloys is reported, where applying a magnetic field adiabatically causes cooling, unlike the conventional magnetocaloric effect (MCE) where removing the field leads to cooling. This inverse effect is observed in some intermetallic compounds, where a moderate entropy increase occurs upon field application. In Ni-Mn-Sn alloys, the entropy change is as large as that of giant MCE materials but with opposite sign, originating from martensitic phase transformations that modify magnetic exchange interactions. The MCE is a temperature change upon adiabatic magnetic field application, leading to spin reordering and cooling. Recent discoveries of giant MCE materials at room temperature have enabled room-temperature refrigeration. The MCE is largest near magnetic transition temperatures, where structural and magnetic phase transitions occur. In Ni-Mn-Sn alloys, the inverse MCE is observed, with entropy changes up to 18 J K⁻¹ kg⁻¹ for x = 0.13 and 15 J K⁻¹ kg⁻¹ for x = 0.15. This effect is due to the coupling between martensitic and magnetic domains, leading to magnetically inhomogeneous states. The Ni-Mn-Sn alloys exhibit structural and magnetic phase transformations, with inverse MCE three times larger than in other materials. The magnetocaloric properties are studied through magnetisation measurements, showing step-like behavior in magnetisation curves. The entropy change is calculated using the relationship ΔS(T,H) = μ₀ ∫₀ᴴ (∂M/∂T)ₕ dH. The results show positive entropy changes in the temperature range M_f < T < M_s, with maximum values of about 18 J K⁻¹ kg⁻¹ for x = 0.13. The inverse MCE in Ni-Mn-Sn alloys is significant, with entropy changes comparable to giant MCE materials. It is the largest observed so far for the inverse MCE and could be used for room-temperature refrigeration. The effect is attributed to the martensitic transition modifying magnetic properties, and the inverse MCE could be used as a heat sink in combination with conventional MCE materials. The study highlights the potential of Ni-Mn-Sn alloys for magnetic refrigeration applications.