Phase stability and magnetocaloric properties of Gd2OS2 and γ-Gd2S3: a combined experimental and theoretical study.

Modifying the crystal structure of materials through thermal treatment and sulphurisation enables the formation of materials that are chemically challenging to stabilize using classical syntheses. This research investigates the effect of synthesis conditions during thermal treatment starting from the sulphide α-Gd2S3 and examines the structural, magnetic, and magnetocaloric properties of γ-Gd2S3 phase and Gd2OS2-rich sample, obtained in a partially sulphurised atmosphere. Both compounds are known to be chemically unstable, prompting us to calculate their phase diagrams using density functional theory (DFT) to better understand their chemical stability. For the first time, the Néel temperature (TN) of antiferromagnetic (AFM) ordering, the effective magnetic moment (μeff), the magnetocaloric effect (MCE), and the magnetic transition temperature (Tr) corresponding to the maximum MCE are reported for the Gd2OS2 oxysulphide and compared with those of α-Gd2S3 and its sub-phases. DFT investigation of the magnetic exchange interactions Jij was conducted to better understand the antiferromagnetic ordering in these systems. The magnetic phase transition was analyzed using the phenomenological universal curve of magnetic entropy change, revealing a first-order magnetic transition for all samples. The structural change from α-Gd2S3 (Pnma space group) to Gd2OS2 (P21/c space group) lowered TN from 10.0 K to 6.9 K and enhanced the MCE by ∼40%, reaching 79 mJ cm-3 K-1 at 6 K for µ0ΔH = 5 T.