Ab initio studies of possible magnetism in a BN sheet by nonmagnetic impurities and vacancies

We performed first-principles calculations to investigate the possible magnetism induced by different concentrations of nonmagnetic impurities and vacancies in a BN sheet. Atoms of Be, B, C, N, O, Al, and Si are used to replace either B or N in the system as impurities. We discuss the changes in the density of states as well as the extent of the spatial distribution of the defect states, the possible formation of magnetic moments, the magnitude of the magnetization energies, and finally the exchange energies due to the presence of these defects. It is shown that the magnetization energy tends to increase as the concentration of the defects decreases in most of the defect systems, which implies a definite preference for finite magnetic moments. The calculated exchange energies are in general tiny but not completely insignificant for two of the studied defect systems, i.e., one with O impurities substituting for N and the other with B vacancies.