Eu 2 ZnGe 2 OS 6 : A Novel Sub‐Kelvin Magnetic Refrigerant With a High‐Spin Shastry‐Sutherland Lattice

ABSTRACT The pursuit of an excellent combination of a low magnetic ordering temperature ( T ord ) and a giant magnetic entropy change (−Δ S m ) remains a key challenge for sub‐Kelvin magnetic refrigerants. Herein, we present a superior sub‐Kelvin magnetic refrigerant Eu 2 ZnGe 2 OS 6 (EZGOS) with a high‐spin ( S = 7/2) Shastry‐Sutherland (SS) lattice. This compound exhibits both an ultra‐low magnetic ordering temperature ( T ord = 280 mK) and a giant low‐field magnetocaloric effect. The maximum magnetic entropy change () under a low‐field change of 0–1 T is comparable to that of commercial Gd 3 Ga 5 O 12 (GGG) under 0–2 T. At a practical application, with initial conditions of 4 K and 4 T, the achievable minimum temperature for polycrystalline EZGOS reaches 358 mK, which is significantly lower than that of the GGG single crystal (601 mK). This work not only provides a competitive sub‐Kelvin refrigerant but also opens up a new avenue for the application of high‐spin SS magnets.