First-Principles Study of Defect-Induced Magnetism in Carbon

We have studied the role of defects on the magnetic properties of carbon materials using first-principles density functional methods. We show that, while the total magnetization decreases both for diamond and graphite with increase in vacancy density, the magnetization decreases more rapidly for graphitic structures. The presence of nitrogen nearby a vacancy is shown to produce larger macroscopic magnetic signals as compared to a standalone carbon vacancy. The results indicate the possibility of tuning magnetization in carbon by controlled defect generation and doping.

Figure 1

Left: the electronic band structure of the diamond with a single vacancy per supercell. Bands for spin-up and spin-down electrons are represented by solid and dashed lines. Right: the dangling $s{p}^3$ hybrids coupled levels split to two groups.

Figure 2

Topological configuration of two vacancies in the diamond supercell. $X_0$ indicates the position of first vacancy, $X_{a-e}$ indicates the relative position of the second vacancy. ${\mathrm{C}}^{†}$ indicates undercoordinated carbon atoms, C indicates fourfold-coordinated carbon atoms.

Figure 3

(a) Topological configuration of two vacancies in the graphite supercell. $X_0$ indicates the position of first vacancy, $X_{a-i}$ indicates the relative position of the second vacancy. (While for the cases of nitrogen implantation, $X_0$ indicates the position of vacancy, $X_{a-i}$ indicates the relative position of the nitrogen atom.) (b) Spin density shown for the 2nd vacancy in the $X_b$ position.