Low-field-driven giant magnetocaloric effect in KGdF4 for sub-Kelvin cryogenic refrigeration

Magnetic refrigeration is a promising technology capable of achieving sub-Kelvin temperatures without using 3 He. However, conventional magnetocaloric materials suffer from drawbacks such as high driving magnetic fields, low magnetic entropy change (Δ S M ), and structural instability, limiting their practical application. In this work, KGdF 4 with different crystal structures was synthesized, and the structure dependence of the magnetocaloric effect (MCE) was investigated. Notably, in the cubic KGdF 4 (C-KGdF 4 ), the chemical disorder of Gd 3+ /K + , increases the Gd 3+ -Gd 3+ distance and weakens the dipolar interactions, and thus leads to a large -Δ S M  = 30.5 J kg −1  K −1 at 1.3 K at the magnetic field change of 10 kOe, which is more than three times of that of the commercial Gadolinium Gallium Garnet (Gd 3 Ga 5 O 12 , GGG) under the same conditions. Furthermore, the magnetic ordering temperature of 0.6 K of the C-KGdF 4 is lower than most reported Gd-based magnetocaloric materials. These excellent magnetocaloric performances suggest that C-KGdF 4 is a highly promising candidate for ultra-low-temperature magnetic refrigeration.