Electronic structure of La_0.7Sr_0.3Mn_1−<i>x</i>Cu_<i>x</i>O₃(0.0≤<i>x</i>≤0.30)

Abstract

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 σpd 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 σpd 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.