Investigation of the obscure spin state of Ti-doped CdSe

Using computational and experimental techniques, we examine the nature of the 2+ oxidation state of Ti-doped CdSe. Through stoichiometry and 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 a 2+ oxidation state. Given the nature of the Ti²⁺ state, we investigate the electronic and magnetic states with density functional theory for a supercell of CdSe with an ultra-low concentration of Ti. We find that reproducing the magnetic moment of spin-1 requires an onsite potential of 4-6 eV must be included. Furthermore, the electronic structure and density of states show the presence of a Ti-d impurity band above the Fermi level and a weakly metallic state for a U = 0 eV. However, the evolution of the electronic properties as a function of the Hubbard U shows that the Ti-d drop below the Fermi around 4 eV with the onset of a semiconducting state. The impurity then mixes with the lower valence bands and produces the 2+ state for the Ti atom.