Electronic and magnetic structure of a 1000 K magnetic semiconductor:: α-hematite (Ti)

There has been much interest in doping traditional semiconductors such as GaAs with Mn or other transition metals in order to obtain semiconductors that are magnetic at room temperature. Some of the goals of this research have been a Curie temperature that exceeds 400 K and the possibility of both n- and p-type doping. An alternative approach is to investigate nontraditional semiconducting materials that are known to be magnetic at room temperature. An example of such a material is solid solutions of the minerals ilmenite (FeTiO3) and alpha-hematite (Fe2O3). In this article we investigate the electronic and magnetic structure of Ti doped alpha-hematite using density functional theory and find within this model: alpha-hematite is an antiferromagnetic insulator with strong ferromagnetic coupling in the cation planes perpendicular to the c axis and antiferromagnetic coupling between these planes. Substitution of Ti for Fe produces a net moment of 4mu(B) and a negative carrier in one spin channel. The negative carrier resides largely on the second nearest neighbor cation sites. The Ti atoms prefer not to sit on adjacent cation planes. Doping alpha-hematite with Ti atoms on alternate cation layers should lead to a ferrimagnetic semiconductor with a magnetic transition temperature of nearly 1000 K. (C) 2003 American Institute of Physics.