Comprehensive DFT investigation of X₂MgSe₄ (X = Dy, Tm) spinels for opto-spintronic and thermoelectric devices

Abstract

Herein, a computational technique known as full potential linearized augmented plane wave (FP-LAPW) is applied for the analysis of magnetic, structural, optical, electronic, and thermoelectric features of X2MgSe4 (X= Dy, Tm) spinels within the density functional theory (DFT). Structural and thermodynamic stabilities are confirmed through the computation of tolerance factor (0.77) and formation enthalpies (-ve) for both spinels. Dy2MgSe4 behaves as a semiconductor with a 1.5 eV direct bandgap (Eg) in the majority spin state but as a metal in the minority spin state, resulting in its half-metallic ferromagnetic (HMF) nature. While Tm2MgSe4 demonstrated a semi-conducting nature in both spin up/down channels, with Eg of 1.41/1.34 eV, respectively. Absorption spectrum displays linear trend with peaks appearing at 6.10 eV for Dy2MgSe4 and 6.46 eV for Tm2MgSe4. Since peaks are appeared in the Ultraviolet (UV) region making them suitable materials for various optoelectronic application, including optical memory devices, sensors and optical filters. The calculated ZT values are 0.77 (at 800 K) and 0.766 (at 300 K), for Dy2MgSe4 and Tm2MgSe4, correspondingly. Overall, the study of X2MgSe4 (X= Dy, Tm) has shown a great potential for their potential usage in energy harvesting and spintronic applications.