Energy Level Spectra of Transition Metal Ions In Diluted Magnetic Semiconductors

ABSTRACTWe present a study of the low lying energy levels of Fe2+, Co2+, Ni2+ and Cu2+ in diluted magnetic semiconductors such as Cd1−xCoxTe and Cd1−xCoxSe and their counterparts. In the first of these compounds the magnetic ion sits on a site of symmetry Td while in the second the symmetry is trigonal (C3v). We develop a formulation that permits a continuous variation from Td to C3v symmetry. Comparison with experimental data in Cd1−xCoxSe shows that the C3v distortion amounts to about 10% of the crystal potential at the Co2+ site. Our study of the energy spectra of Fe2+ in Td and C3v crystal potentials reveals that, even in the cubic field, the levels exhibit an anisotropy which manifests it- self in an anisotropy of the magnetization, , in the regime in which is not a linear function of the magnetic field . The study includes all the levels in the lowest terms of the (3d)n (n=6,7,8,9) configurations. The calculations are carried out to second order in the spin-orbit interaction and in for the lowest orbital states and to first order in for the excited states. The g-factors of all the levels are obtained including their anisotropy for the Co2+ and Cu2+Γ8states.