First-principles investigations on the electronic structure, optical properties, and giant magnetic-optical Kerr effect in double-perovskite Ba2NiBO6 (B = Os, Ir)

Abstract

The hybrid 3d–5d transition-metal oxides have been frequently studied for their novel electronic and magnetic properties, in which the strong spin-orbit coupling (SOC) effect is added to the interplay among charge, spin, and orbital degrees of freedom. Recently, perfectly ordered 3d–5d double-perovskite oxides of Ba2NiOsO6 and Ba2NiIrO6 were synthesized: Ba2NiOsO6 was measured to be a rare ferromagnetic semiconductor and predicted to have a giant magneto-optical Kerr effect (MOKE); and Ba2NiIrO6 showed a competition between antiferromagnetic and ferromagnetic interactions. In this work, we systematically investigated the magnetic, electronic, and optical properties, as well as the MOKE of Ba2NiBO6 (B = Os, Ir) using density functional theory. The long-ranged B–B interaction was found to play a key role in determining the magnetism of the compounds. For Ba2NiOsO6, the experimentally observed semiconductive nature was reproduced only by taking into account both the electron correlation and SOC effect. In Ba2NiIrO6, however, the SOC effect on 5d Ir was weak. Owing to the d→d or p→d interband transitions, both materials had a strong absorption in the ultraviolet–visible spectral region. In particular, the absorption spectrum of Ba2NiIrO6 covered almost the entire visible region. They also exhibited considerable MOKE in the visible region. The maximum of Kerr rotation for Ba2NiOsO6 and Ba2NiIrO6 could reach 5.3° and 4.1°, respectively. The characteristics of the Kerr spectra were primarily dominated by the off-diagonal optical conductivity, which reflects the contributions of band exchange splitting and SOC to MOKE. The Ba2NiBO6 (B = Os, Ir) are very promising optoelectronic and magneto-optical materials.