Achieving Magnetic Refrigerants with Large Magnetic Entropy Changes and Low Magnetic Ordering Temperatures.

Adiabatic demagnetization refrigeration (ADR) is a promising cooling technology with high efficiency and exceptional stability in achieving ultralow temperatures, playing an indispensable role at the forefront of fundamental and applied science. However, a significant challenge for ADR is that existing magnetic refrigerants struggle to concurrently achieve low magnetic ordering temperatures ( T 0 ) and substantial magnetic entropy changes (-Δ S m ) at ultralow temperatures. In this work, we propose the combination of Gd 3+ and Yb 3+ to effectively regulate both -Δ S m and T 0 in ultralow temperatures. Notably, the -Δ S m values for Gd 0.1 Yb 0.9 F 3 ( 1 ) and Gd 0.3 Yb 0.7 F 3 ( 2 ) in the 0.4-1.0 K range exceed those of all previously reported magnetic refrigerants within this temperature interval, positioning them as the most efficient magnetic refrigerants for the third stage to date. Although the -Δ S m values for Gd 0.5 Yb 0.5 F 3 ( 3 ) in 1-4 K are less than those of the leading magnetic refrigerant Gd(OH)F 2 , the -Δ S m values for Gd 0.7 Yb 0.3 F 3 ( 4 ) in 1-4 K at 2 T surpass those of all magnetic refrigerants previously documented within the same temperature range, making it the superior magnetic refrigerant for the fourth stage identified thus far.