Electronic and magnetic structure of transition-metal-doped α -hematite

We investigate the electronic and magnetic structure of transition-metal-doped $\ensuremath{\alpha}$-hematite using the local density approximation with local correlations $(\mathrm{LDA}+U)$. The dopants in this study are the $3d$ transition metals $\mathrm{Sc}\text{\ensuremath{-}}\mathrm{Zn}$ and Ga and are assumed to substitute on an Fe site. The calculated net moment per substitutional impurity is found to be $\ensuremath{\mid}{z}_{D}\ensuremath{-}{z}_{\mathit{Fe}}\ensuremath{\mid}$, opposite to that of the replaced Fe, where ${z}_{D}$ and ${z}_{\mathit{Fe}}$ are the numbers of valence electrons of the dopant and Fe, respectively. The dopants, D, substitute in an effective charged state ${\mathrm{D}}^{3+}$ except for ${\mathrm{Ti}}^{4+}$ and ${\mathrm{Zn}}^{2+}$. In the case of Ti, the extra electron converts a neighboring ${\mathrm{Fe}}^{3+}$ atom to ${\mathrm{Fe}}^{2+}$. In the case of Zn, the missing electron generates a relatively diffuse hole at the top of the valence band spread over neighboring O atoms.