Computational investigation of the spin-1 state of Ti-doped CdSe

Using computational and experimental techniques, we examine the 2+ oxidation state of Ti when doped into CdSe. Through stoichiometry and confirmed through magnetization measurements, the weakly-doped material of Cd_1-xTi_xSe (x = 0.0043) shows the presence of a robust spin-1 magnetic state of Ti, which is indicative of the 2+ oxidation state. Given the obscure nature of the Ti²⁺ state, we investigate the electronic and magnetic states using density functional theory. Using a GGA+U basis, we determine the electronic structure, magnetic moment density, and optical properties for a supercell of CdSe with an ultra-low concentration of Ti. We find that an onsite potential of 4-6 eV must be included in order to reproduce the magnetic moment of spin-1. The evolution of the electronic properties as a function of the Hubbard U shows that the Ti-d orbital drops below the Fermi around U = 4 eV along with the onset of a semiconducting state, and the impurity state mixes with the lower valence bands to produce the 2+ state for the Ti atom.