Magnetism in two-dimensional BN1-xOx and B1-xSixN: Polarized itinerant and local electrons

We use density-functional theory based first-principles methods to study the magnetism in a two-dimensional hexagonal BN sheet induced by the different concentrations of oxygen and silicon atoms substituting for nitrogen (O-N) and boron (Si-B), respectively. We demonstrate the possible formation of three distinct phases based on the magnetization energy calculated self-consistently for the ferromagnetic (MEFM) and antiferromagnetic (MEAFM) states, i.e., the paramagnetic phase with MEFM=MEAFM, the ferromagnetic phase with MEFM > MEAFM, and finally the polarized itinerant electrons with finite MEFM but zero MEAFM. While the O-N system was found to exist in all three phases, no tendency toward the formation of the polarized itinerant electrons was observed for the Si-B system though the existence of the other two phases was ascertained. The different behavior of these two systems is associated with the diverse features in the magnetization energy as a function of the oxygen and silicon concentrations. Finally, the robustness of the polarized itinerant electron phase is also discussed with respect to the O substitute-atom distributions and the applied strains to the system.