K(Gd0.1Yb0.9)3F10, A Promising Refrigerant for sub-100 mK Adiabatic Demagnetization Refrigeration

Abstract

Ultralow-temperature refrigeration is indispensable for advancing quantum technologies and astrophysical instrumentation operating below 1 K. Adiabatic demagnetization refrigeration (ADR) offers a reliable and efficient alternative to ³He-based systems, but progress has been limited by the modest magnetic entropy change (-ΔS_m) of commercial refrigerants at subkelvin temperatures. Here, we report K(Gd_0.1Yb_0.9)₃F₁₀ (1), a dense lanthanide fluoride synthesized by partially substituting Gd³⁺ into KYb₃F₁₀, as a high-performance refrigerant for ADR. Owing to weak magnetic interactions and the absence of longrange ordering down to 50 mK, 1 delivers substantial -ΔS_m values across 0.3-1.0 K. When integrated into a two-stage ADR system, 1 achieves a minimum temperature of 67 mK, a remarkable cooling capacity of 607.82 mJ and load-free operation for over 30 h at 300 mK under residual magnetic field of 1.03 T. These results position the refrigerator loaded with K(Gd_0.1Yb_0.9)₃F₁₀ as a promising alternative to ³He-based systems near 300 mK and underscore its potential for practical helium-free cryogenic applications in quantum technologies and space platforms.