The electronic structure of Fe-doped ${\mathrm{SnO}}_2$ is systematically investigated by means of first-principles calculations. A ferrimagnetic exchange interaction between the dopants, which is rarely found in dilute magnetic semiconductors, is predicted for the ground doping configuration in which two Fe ions are adjacently substituting the Sn sites in a distorted rutile structure. Spin density results reveal the direct exchange interaction between $\mathrm{O}2p$ and $\mathrm{Fe}3d$ electrons with antiparallel spins, which leads to competition between ferromagnetic and antiferromagnetic superexchange interactions since the doping ions tend to form a special $120°$ $\mathrm{Fe}\text{–}\mathrm{O}\text{–}\mathrm{Fe}$ bond. Therefore, a negligible energy difference between the parallel and antiparallel spin alignments is predicted for the ground-state configuration. Moreover, the calculated density of states with both parallel and antiparallel spins shows the nearly 100% spin-polarized states at the Fermi level. An interesting half-metallic antiferromagnetic state reported recently has been also obtained in one of the calculated doping configurations.

• Received 21 November 2006

DOI:https://doi.org/10.1103/PhysRevB.75.094412