Room-Temperature Ferromagnetism in Carbon-Doped ZnO

We report ferromagnetism in carbon-doped ZnO. Our first-principles calculations based on density functional theory predicted a magnetic moment of $2.02{\mu }_B$ per carbon when carbon substitutes oxygen in ZnO, and an ferromagnetic coupling among magnetic moments of the carbon dopants. The theoretical prediction was confirmed experimentally. C-doped ZnO films deposited by pulsed-laser deposition showed ferromagnetism with Curie temperatures higher than 400 K. The measured magnetic moment based on the content of carbide in the films [$(1.5–3.0){\mu }_B$ per carbon] was in agreement with the theoretical prediction. The magnetism is due to the Zn-C system in the ZnO environment.

Figure 1

Calculated total (top panel) and local density of states for the carbon dopant and a neighboring Zn atom. The Fermi level is indicated by the dashed vertical line.

Figure 2

$M_s(T)/M_s(5\mathrm{K})$ versus temperature for samples B and C. The solid lines are a guide for the eye. The inset shows the hysteresis loop of sample B taken at 300 K.

Figure 3

The room-temperature saturation magnetization $M_s$ and the magnetic moment per carbon in the carbide state (carbide carbon) as a function of the measured carbon concentration of the C-doped specimens. The carbon concentration in the sample was estimated by SIMS measurements, while the percentage of carbon in the carbide state was estimated by XPS measurements.

Figure 4

The Hall voltage as a function of magnetic field for sample B at different temperatures. The inset shows the Hall effect curve at 10 K after the normal part is removed.