Effect of sp hybridization and bond-length disorder on magnetism in amorphous carbon- A first-principles study

Abstract

Magnetism in amorphous carbon system is investigated using first-principle molecular dynamics (MD) and constrained magnetic calculations. The existing literature suggests that sp2-like 3-fold coordinated carbon atoms only play a significant role in obtaining magnetism in amorphous carbon. The present calculations predict the role of the sp1 hybridised atom and the presence of bond-length disorder in sustaining the magnetic moment in the amorphous carbon system. For a low-density amorphous carbon structure with a typical density of 1.0 g/cm3 and below, the sp1-like 2-fold coordinated carbon atoms play an essential role instead of the sp2 atom. In the intermediate density regime, i.e., between 1.0 g/cm3 to 3.0 g/cm3, apart from sp1 or sp2 fraction, the effect of variation in bond length is observed to play a vital role to sustain magnetism in the amorphous carbon system. The origin of magnetism in Q‑carbon in terms of bond-length disorder and change in hybridization ratio is explained.