Role of d-d and p-d hybridization in CoTi-based magnetic semiconductors with 21 and 26 valence electrons

We have found that CoTiFeP, CoTiFeAs and CoTiFeSb with 26 valence electrons are magnetic semiconductors by first-principles calculations. The electronic structure, magnetic propeties and origin of the band gap are investigated and compared with the magnetic semiconductor CoTiVAl with 21 valence electrons. It has been found that the magnetic moment in CoTiVAl mainly originates from the large exchange splitting effect of the V atom, which carries the largest magnetic moment of 2.14 mu(B), parallel to those of Co and Ti, while in CoTiFeZ (Z = P, As, Sb) compounds, the moments mainly originate from Co and Fe atoms. The atomic moments of Co and Fe are in an antiparallel arrangement with the moments of their nearest neighbors' Ti atoms at the B site due to the strong hybridization between Co-3d, Fe-3d and Ti-3d electrons. Based on the classical molecular orbital hybridization theory, different origins of the gap in 21 and 26 valence electrons are analyzed. It is confirmed that p-d hybridization is significant for opening up the band gap, for adjusting the position of the Fermi level and the width of the band gap in our magnetic semiconductors. This will provide practical guidance for searching for new magnetic semiconducting materials.