Magnetic, optoelectronic, and thermoelectric characteristics of Ln2MnSe4 (Ln = Yb, Lu) spinel chalcogenides: A DFT investigation

Herein, structural, optical, magnetic, electronic, and thermoelectric (TE) characteristics of cubic spinels Ln2MnSe4 (Ln = Yb, Lu) are examined by DFT + U. Enthalpy of formation (& UDelta;Hf) for both spinels are negative (-3.189 and -2.251 eV for Yb2MnSe4 and Lu2MnSe4, correspondingly), which supports thermodynamical stability for both spinels. Spin dependent band structures and density of state (DOS) disclose the half metallic and magnetic semiconducting nature for both Ln2MnSe4 (Ln = Yb, Lu) spinels, respectively, with direct bandgaps of 1.44 eV in spin up and metallic in spin down for Yb2MnSe4 whereas Lu2MnSe4 has 0.5/1.5 eV in spin up/down channel. Optical response of Ln2MnSe4 (Ln = Yb, Lu) spinels is also determined. At 0 eV, the computed results of refractive index n (& omega;) for Yb2MnSe4/Lu2MnSe4 are 12.0/2.89, respectively. For Yb2MnSe4 and Lu2MnSe4 peak value of & sigma;(& omega;) are calculated as 7813.08 at 7.03 eV and 7532.71 (1/& omega;cm) at 6.47 eV, respectively. To assess the temperature dependent transport behavior of both compounds, thermoelectric (TE) characteristics including power factor (PF), Seebeck coefficient (S), thermal conductivity (k/& tau;), electrical conductivity (& sigma;/& tau;) and figure of merit (ZT) are determined. Maximum ZT values for Yb2MnSe4 and Lu2MnSe4 are 0.18 and 0.79 at 800 K, correspondingly. Results show that Yb2MnSe4 is suitable contender spintronics due to 100% spin polarization at Fermi level whereas Lu2MnSe4 is useful addition to magnetic semiconductor family having potential applications in opto-electronic and TE devices.