A promising magnetocaloric effect has been obtained in Ni–(Co)–Mn–X (X = Sn, In, Sb)-based Heusler alloys, but the low isothermal magnetic entropy change ΔS M restricts the further promotion of such materials. Defect engineering is a useful method to modulate magnetic performance and shows great potential in improving the magnetocaloric effect. In this work, dense Ni vacancies are introduced in Ni41Mn43Co6Sn10 alloys by employing high-energy electron irradiation to adjust the magnetic properties. These vacancies bring about intense lattice distortion to change the distance between adjacent magnetic atoms, leading to a significant enhancement of the average magnetic moment. As a result, the saturation magnetization of ferromagnetic austenite is accordingly improved to generate a high isothermal magnetic entropy change ΔS M of 20.0 J/(kg K) at a very low magnetic field of ∼2 T.

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