s The geometrical structures of Cd0.75TM0.25Se （TM = Ti, V, Cr and Mn） are optimized, and then their electric and magnetic properties are investigated by performing first-principles calculations within the generalized gradient approximation for the exchange-correlation function based on density functional theory. Cd0.75TM0.25Se （TM =Ti and V） are found to have high spin-polarization near 100% at the Fermi level. Cd0.75TM0.25Se （TM = Cr and Mn） are half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely ＋100%. The supercell magnetic moments of Cd0.75Cr0.25Se and Cdo.75Mno.25Se are 4.00 and 5.00 μB, which arise mainly from Cr-ions and Mnions, respectively. The half-metallicity of Cdo.75Cro.25Se is more stable than that of Cd0.75Mn0.25Se. The electronic structures of Cr-ions and Mn-ions are Cr eg2↑t22g↑ and Mn e2 3 ↑t23g↑, respectively.
