First-principles calculations concerning ferromagnetism in Q-carbon

Abstract

Spin-constrained first-principles calculations were performed to assess amorphous carbon systems having a density of 5.24, 5.46 or 5.63 g/cm³. The liquid quenching method was employed to produce suitable amorphous structures, and analyses of radial distribution functions, distributions of local magnetic moments and partial electronic densities of states were carried out. The system with a magnetic moment of 0.4 μ_B/atom and density of 5.63 g/cm³ was found to possess a high proportion (approximately 72.1 %) of sp³ hybridized carbon atoms. This result was in good agreement with recent experimental evaluations of ferromagnetic Q‑carbon. The simulations also indicated that unpaired electrons will be present in two types of sp² hybridized carbon atoms and that these electrons are largely responsible for ferromagnetism in Q‑carbon. The present work provides an important starting point that will assist in understanding the nature of this material and promote the study of high-density Q‑carbon materials with novel physical properties.