Magneto Caloric Properties of Polycrystalline Gd₂O₂S for an Adiabatic Demagnetization Refrigerator

Abstract

Abstract. Currently, many space missions that use cryogenic equipment are being planned. In particular, high resolution sensors, such as transition edge sensors, require very low operating temperatures, below 100 mK. Adiabatic demagnetization refrigerator (ADR) systems are a useful tool for producing ultra-low temperatures in space because these devices can operate independently of gravity. The magnetic material is one of the most important components with respect to effectiveness of the cooling power. Thus, we could increase the cooling power using a magnetic material that has a large entropy change over the operating temperature range. Polycrystalline Gd2O2S (GOS), which was developed by Numazawa et al, can be used as such as a magnetic regenerator material. Furthermore, GOS has a very large specific heat and a magnetic phase transition temperature of about 5.2 K. These features make GOS suitable for use in the high temperature stage of an ADR. In this study, we measured and evaluated the physical properties of GOS for applications to ADRs.

NaGdS2: A Promising Sulfide for Cryogenic Magnetic Cooling

“…Surprisingly, only a few articles focused on the magnetocaloric properties of inorganic sulfides and oxysulfides. − EuS is characterized by a significant magnetocaloric effect at T C = 16.5 K, with a maximum magnetic entropy change from bulk of 16.8 and 28.4 J kg –1 K –1 for magnetic field changes of 2 and 5 T, respectively . Orthorhombic α-Ln 2 S 3 (Ln = Tb, Dy) compounds are characterized by two successive antiferromagnetic transitions ( T N < 15 K), which can be shifted to either lower or higher temperatures (depending on the crystal orientation) by a magnetic field change, reflecting a strong magnetic anisotropy of the materials .…”