Strain energy enhanced room-temperature magnetocaloric effect in Mn₅Ge₃

Large magnetic entropy change (ΔS_M) can realize a prominent heat transformation under the magnetic field and directly strengthen the efficacy of the magnetocaloric effect, which provides a pioneering environmentally friendly solid-state strategy to improve refrigeration capacities and efficiencies. The second-order magnetic transition (SOMT) materials have broader ΔS_M peaks without thermal hysteresis, making them highly attractive in magnetic refrigeration, especially in the room temperature range. Here, we report a significant enhancement of ΔS_M at room temperature in single-crystal Mn₅Ge₃. In this SOMT system, we realize a 60% improvement of $-\mathrm{\Delta }{S}_{\mathrm{M}}^{\max }$ from 3.5 J/kg⋅K to 5.6 J/kg⋅K at T = 300 K. This considerable enhancement of ΔS_M is achieved by intentionally introducing strain energy through high-pressure constrained deformation. Both experimental results and Monte Carlo simulations demonstrate that the enhancement of ΔS_M originates from the microscopic strain and lattice deformation induced by strain energy after deformation. This strain energy will reconstruct the energy landscape of this ferromagnetic system and enhance magnetization, resulting in a giant intensity of magnetocaloric responses. Our findings provide an approach to increase magnetic entropy change and may give fresh ideas for exploring advanced magnetocaloric materials.