New ferromagnetic semiconductor double perovskites: La₂FeMO₆ (M = Co, Rh, and Ir)

Density functional theory with generalized gradient approximation (GGA) plus onsite Coulomb interaction (GGA + U) was used to calculate physical proprieties of new ferromagnetic semiconductor materials of the La₂FeMO₆ (M = Co, Rh, and Ir). We calculate the 406 (C₂²⁹) La₂MM′O₆ compounds which MM′ can be any pair taken from the 29 transition metal elements except La. La₂FeCoO₆ is a potential candidate for ferromagnetic semiconductor. For the GGA + U scheme, La₂FeCo₆ remains a stable FM semiconductor, whereas La₂FeRhO₆ and La₂FeIrO₆ are shown the FM and AFM states of which are degenerate with each other. The FM semiconductor gap remains in existence under tensile or compressive strain in La₂FeRhO₆ and La₂FeIrO₆. The superexchange interaction in ferromagnetic La₂FeMO₆ (M = Co, Rh, and Ir) is high spin (HS) Fe completely empty e_g orbital hopping to the half-filled (LS) Co (Rh and Ir) empty e_g orbital.