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

Abstract

Magnetic refrigeration is a promising technology capable of achieving sub-Kelvin temperatures without using ³He. However, conventional magnetocaloric materials suffer from drawbacks such as high driving magnetic fields, low magnetic entropy change (ΔS_M), and structural instability, limiting their practical application. In this work, KGdF₄ with different crystal structures was synthesized, and the structure dependence of the magnetocaloric effect (MCE) was investigated. Notably, in the cubic KGdF₄ (C-KGdF₄), the chemical disorder of Gd³⁺/K⁺, increases the Gd³⁺-Gd³⁺ distance and weakens the dipolar interactions, and thus leads to a large -ΔS_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 (Gd₃Ga₅O₁₂, GGG) under the same conditions. Furthermore, the magnetic ordering temperature of 0.6 K of the C-KGdF₄ is lower than most reported Gd-based magnetocaloric materials. These excellent magnetocaloric performances suggest that C-KGdF₄ is a highly promising candidate for ultra-low-temperature magnetic refrigeration.