Gd(OH)F₂: A Promising Cryogenic Magnetic Refrigerant

Abstract

Magnetic refrigerants with a large magnetocaloric effect (MCE) in a wide temperature range and low magnetic ordering temperature (<i>T</i>_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 <i>T</i>_o, weak magnetic interaction, and high magnetic density. Here, we report the syntheses, heat capacities, and magnetic properties of Gd(OH)_3-<i>x</i>F_<i>x</i> (<b>1</b>: <i>x</i> = 1, <b>2</b>: <i>x</i> ≈ 1.5, and <b>3</b>: <i>x</i> = 2), demonstrating for the first time that the introduction of fluoride anions into antiferromagnetic Gd(OH)₃ can effectively regulate its <i>T</i>_o. Significantly, <b>3</b> not only has a <i>T</i>_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.