Electronic structure of La0.7Sr0.3Mn1−xCuxO3 (0.0≤x≤0.30)

We have investigated the electronic structure of Cu-substituted La0.7Sr0.3MnO3 (LSMO) by x-ray photoelectron spectroscopy and using density functional theory within local spin-density approximations (LSDA) and LSDA+U. We find that there is a coexistence of mixed-valent Cu ions, Cu3+ with Cu2+ dominant, in all Cu-substituted LSMO samples. From a deconvolution of the XPS spectra of Cu-2p3/2, we determined the ratios of Cu2+/Cu3+ and Mn3+/Mn4+, and in turn calculated the change in the tolerance factors of Cu-substituted LSMO. Valence-band photoelectron spectra show that the density of states at the Fermi level is made up mainly of the O-2p and Mn-3d states with a small contribution near EF from the Cu-3d states. We find that LSDA+U calculations for La1/2Sr1/2Mn1-xCuxO3 describe the half-metallicity and ground state ferromagnetic ordering with no evidence of antiferromagnetism for all systems consistent with experimental neutron diffraction data. Two electron transport channels of the major Mn-O-Mn and the minor Cu-O-Cu chains are found. This suggests that the electronic transport behavior of Cu-substituted LSMO systems may be explained by a combination of two different transport mechanisms: (i) a sigmapd hybridization between the eg states in a majority spin-up Mn-d channel with O-2p orbitals in the Mn-O-Mn chain and (ii) a sigmapd hybridization between the eg states in a dominant minority spin-down Cu-d channel with O-2p orbitals in the Cu-O-Cu chain. We also find that the half-metallicity of the compounds is lost upon Cu-substitution with a resulting anisotropic electronic transport of the Cu-pair electrons in the basal plane and along the c axis.