Refrigeration down to 0.16 K using a frustrated magnet Gd₂B₂MoO₉

Magnetic refrigeration, utilizing the magnetocaloric effect in solid-state magnets, has emerged as a promising cooling technology. The development of practical ultra-low-temperature magnetic refrigeration applications has been limited by the absence of high-performance magnetic refrigerants. Herein, we provide a frustrated Gadolinium-dominated magnet, Gd₂B₂MoO₉ oxide, which exhibits remarkable ultra-low temperature magnetocaloric performances. The maximum magnetic entropy changes reach 13.3 (76.6), 33.7 (194.0) and 45.1 (259.8) J/kgK (mJ/cm³K) under relatively low magnetic field changes of 0-1, 0-2 and 0-3 T, respectively. A minimum temperature of 0.16 K has been achieved by a custom-built quasi-adiabatic demagnetization apparatus. These magnetocaloric performances surpass those of the commercial ultra-low temperature magnetic refrigerant Gd₃Ga₅O₁₂ and outperform most of recently reported materials. Combined with its relatively high density and environmental stability, the geometrically frustrated Gd₂B₂MoO₉ oxide is established as an attractive ultra-low temperature magnetic refrigerant.