Insulating ferromagnetism in La4Ba2Cu2O10: an Ab initio wannier function analysis.

摘要: Microscopic mechanisms of the puzzling insulating ferromagnetism half-filled ${\mathrm{L}\mathrm{a}}_{4}{\mathrm{B}\mathrm{a}}_{2}{\mathrm{C}\mathrm{u}}_{2}{\mathrm{O}}_{10}$ are elucidated with energy-resolved Wannier states. The dominant magnetic coupling, revealed through evaluated parameters ($t$, $U$, and $J$), turns out to be intersite direct exchange, a currently ignored mechanism that overwhelms antiferromagnetic superexchange. By contrast, isostructural ${\mathrm{N}\mathrm{d}}_{4}{\mathrm{B}\mathrm{a}}_{2}{\mathrm{C}\mathrm{u}}_{2}{\mathrm{O}}_{10}$ develops observed order via its characteristics 1D chain. Surprisingly, in-plane both cases is not controlled by coupling between nearest neighbors. An intriguing pressure-induced ferromagnetic transition predicted.