Gd(OH)F 2 : A Promising Cryogenic Magnetic Refrigerant.

Magnetic refrigerants with a large magnetocaloric effect (MCE) in a wide temperature range and low magnetic ordering temperature ( T o ) in the sub-kelvin temperature region are not only crucial for adiabatic demagnetization refrigeration but also open up a broader parameter space for the optimal design of adiabatic demagnetization refrigerators. However, such magnetic refrigerants are extremely rare because they require magnetic materials to simultaneously satisfy three conditions: low T o , weak magnetic interaction, and high magnetic density. Here, we report the syntheses, heat capacities, and magnetic properties of Gd(OH) 3- x F x ( 1 : x = 1, 2 : x ≈ 1.5, and 3 : x = 2), demonstrating for the first time that the introduction of fluoride anions into antiferromagnetic Gd(OH) 3 can effectively regulate its T o . Significantly, 3 not only has a T o of 0.5 K but also exhibits a large MCE in the temperature range from 0.5 to 4 K, representing the best magnetic refrigerant reported to date in the temperature range of 0.5-4 K from the viewpoint of the MCE.