Title: Exceptional Cooling Capacity of LiGd0.1Yb0.9F4 at Sub-Kelvin Temperatures

Authors: Qiao-Fei Xu, Peng Zhao, Man-Ting Chen, Ruo-Tong Wu, Wei Dai*, La-Sheng Long*, Lan-Sun Zheng

Abstract: Adiabatic demagnetization refrigeration, which utilizes the magnetocaloric effect of magnetic refrigerants, stands as the sole cooling technology capable of achieving sub-Kelvin temperatures efficiently and reliably without relying on scarce ³He resources or gravity. However, current sub-Kelvin magnetic refrigerants encounter challenges such as structural instability in vacuum or under mild heating, along with small magnetic entropy change (−ΔS_m) values, which significantly limit their practical applications. Here a water-free magnetic refrigerant, LiGd_0.1Yb_0.9F₄ is reported, prepared by introducing Li⁺ ions to reduce the dipolar interactions between Gd³⁺ ions and/or Yb³⁺ ions. Notably, this refrigerant possesses a magnetic ordering temperature of 85 mK, while its experimental −ΔS_m reaches up to 136 mJ cm⁻³ K⁻¹ (0.68 K and 2 T), more than three times the theoretical value of CrK(SO₄)₂·12H₂O. Significantly, this refrigerant not only cools the test sample to temperatures as low as 160 mK but also achieves a specific cooling capacity of 46.943 mJ cm⁻³ T⁻¹ at 300 mK. Remarkably, the specific cooling capacity at 300 mK is more than double that of commercial CrK(SO₄)₂·12H₂O, representing one of the most notable values reported among all known magnetic refrigerants operating at sub-Kelvin temperatures.

Full-Link: https://advanced.onlinelibrary.wiley.com/doi/10.1002/adma.202414226