Robust half-metallic ferromagnet in doped double perovskite Sr2TiCoO6 by rare-earth elements for photovoltaic and thermoelectric conversion: A DFT method

In this study, we have discovered a novel candidate series of half-metals by replacement of the Ti atom with the rare-earth elements RE (=Dy, Ho, Er, or Tm) in the double perovskite Sr2TiCoO6. We methodically investigated the electronic, magneto-optical, and thermoelectric characteristics of the compounds Sr2(RE)CoO6 using the FP-LAPW method. The spin-polarized electronic structure studied within GGA-WC and GGA + U showed a robust half-metallic character for all compounds. The substitution by the rare-earth elements RE enhanced the magnetic characteristics of Sr2TiCoO6, which exhibits a transition from a total magnetic moment of 1μB for Sr2TiCoO6 to 7μB, 6μB, 5μB, and 4μB for Sr2DyCoO6, Sr2HoCoO6, Sr2ErCoO6, and Sr2TmCoO6, respectively. However, the hybridization between RE-4f, Co-3d, and O-2p is responsible for robust half-metallic ferromagnet in Sr2(RE)CoO6 compounds. We have also studied the effect of spin-orbit coupling (SOC) on electronic structure. The Sr2DyCoO6, Sr2HoCoO6, and Sr2ErCoO6 compounds maintained their half-metallicity under GGA + SOC, whereas Sr2TmCoO6 became a magnetic metal. An in-depth analysis of the optical and thermoelectric characteristics was performed by GGA + U. According to the absorption coefficient and imaginary part of the dielectric function, we have found that the compounds Sr2(RE)CoO6 have better absorption quantities at different frequencies (IR, visible, and UV) than Sr2TiCoO6. Due to their high ZT and good Seebeck coefficient in a spin-up canal, the investigated compounds have excellent thermoelectric efficiency. These characteristics make the double perovskites Sr2(RE)CoO6 as a high absorber an attractive choice for photovoltaic solar cells and thermoelectric applications.