Structure, spectrum, magnetic, and transport properties of the compounds Cu_(1-x)Li_xCr_2Se_4 (x=00.7) have been experimentally investigated. X-ray photoelectron spectroscopy spectra (XPS) suggest dominant monovalent Cu~+ in the samples. With Li~+ substitution for Cu~+, the ground state changes from ferromagnetic metal to ferromagnetic insulator due to the suppression of the holes in a ligand Se pCu d orbitals, leading to the decrease of the saturation moment Ms. Both the spectrum and the magnetic results suggest that Lotgering's model of Cu ~+Cr~(3+)_2Se_4 is relevant. There is an inner compressive strain in the system, which results in thermal hysteresis in M(T) and ρ(T) curves.
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