Systematic investigation of magneto-electronic, structural, thermoelectric and optical properties of Nd2MgX4 (X = S, Se) compounds

Abstract

The structural, magnetic, optoelectronic, and thermoelectric (TE) characteristics of Nd2MgX4 (X = S, Se) are determined by utilizing the density functional theory (DFT) based full potential linearized augmented plane wave (FP-LAPW) method as employed in WEIN2k code. The exchange and correlation energies along with Coulomb interactions are brought into consideration by employing local density of approximation with Hubbard model (LDA+U). Tolerance (τ) factor and formation enthalpy were utilized to confirm the stability of both spinels. τ values are 0.70 and 0.68, and formation enthalpy values are (ΔHf) are -3.34 eV and -2.19 eV for Nd2MgX4 (X = S, Se), respectively. For Nd2MgX4 (X = S, Se) metallic behavior is found in spin up case while considerable bandgaps are found in spin down with half metallic bandgap (Eg) values of 1.82 and 1.26 eV (in spin down), correspondingly. The calculated magnetic moment for Nd2MgX4 (X = S, Se) are 12.0008 μB and 12.0003 μB, respectively. Furthermore, optical features including refractive index n(ω), dielectric constant 𝜀𝜀(𝜔𝜔), reflectivity R(ω), optical conductivity σ(ω), absorption coefficient α(ω) and extinction coefficient k(ω) are computed. The maximum calculated real part of dielectric constant 𝜀𝜀1(𝜔𝜔) values for Nd2MgX4 (X = S, Se) are 9.2 and 10.8, respectively. For Nd2MgX4 (X = S, Se), σ(ω) has maximum value of 7642.9 at 6.6 and 7592.5 (Ω cm)-1 at 5.99 eV, respectively. The various temperature dependent thermoelectric (TE) parameters along with figure of merit (ZT) are determined to get full insight into the TE behavior for both compounds by using BoltzTraP code. The computed ZT value for Nd2MgSe4 is 0.81 at 800 K while Nd2MgS4 has ZT value of 0.80 at 800 K. Results showed that both spinels have potential in spintronics and in cooling industries.