Doped semiconductors as half-metallic materials: Experiments and first-principles calculations of CoTi_1-xM_xSb (M = Sc, V, Cr, Mn, Fe)

This work reports experiments and first-principles calculations on the substitutional semiconducting C1(b) compound CoTi1-xMxSb. Diluted magnetic semiconductors have been prepared by substituting titanium in the semiconducting compound CoTiSb by other 3d transition elements M. Self-consistent calculations of the electronic structure predict some of the materials to be half-metallic ferromagnets. The structural, electronic, electric, and magnetic properties of the pure and substituted materials have been investigated. It is found from the experiments that substitution of up to 10% Ti by Fe, Mn, Cr, and V does not affect the crystalline structure and the lattice mismatch is less than 0.5% in the substituted compounds. The electric properties can be tuned from semiconducting to metallic by using different dopants. The M=Cr-doped compound exhibits a metal to semiconductor transition. Photoemission spectroscopy and conductivity measurements agree well with the calculated electronic structure. The measured Curie temperature of the Fe-substituted alloy is far above room temperature (>700 K). This fact and the very low lattice mismatch between the substituted and the pure compound make this material a serious candidate for future electronic applications, in particular for magnetoelectronics and spintronics