Propriedades eletrônicas e magnéticas de filmes ultrafinos de La0,67 Sr0,33 MnO3.

Abstract

Complex oxides have received great attention in the current technological and scientific scenario for exhibiting promising multifunctional and emergent properties. These arise from the strong electron-electron correlation and the interplay between lattice, orbital, charge and spin ordering. Specifically, the La0.67Sr0.33MnO3 (LSMO) is a ferromagnetic half-metal with perovskite structure, presenting almost 100% spin polarization at room temperature, what makes it very interesting for applications in spintronics and oxide-based devices. However, the formation of magnetic dead layers (MDL) at thin films interfaces represents an obstacle for the development of new devices. Although previous studies have attributed the formation of MDL to strain, oxygen vacancies and cation non-stoichiometry, its microscopic origin is still not entirely clear. In this work, we grew, by pulsed laser deposition, epitaxial ultrathin films of LSMO (thicknesses between 1.2 and 8.4 nm) on SrTiO3 (001) single crystals in order to verify whether the oxidation state of manganese (Mn) and/or an orbital reconstruction at the LSMO interfaces could be related to the formation of the MDL. The samples’ crystalline structure and surface morphology was studied by x-ray scattering techniques and atomic force microscopy (AFM). The samples’ electronic structure was investigated by Mn L2,3-edge and O K-edge X-ray absorption spectroscopy (XAS) and X-ray linear dichroism (XLD). The magnetic properties were investigated by Mn L2,3-edge X-ray magnetic circular dichroism (XMCD) and vibrating sampling magnetometer. Our results suggest a reduction in the Mn valence and a consequent decrease in the magnetic moment as the LSMO thickness decreases. We also observe a breakdown in the eg orbitals degeneracy at the LSMO surface, leading to an orbital reconstruction. Our results corroborate the formation of MDL at the surfaces of the ultrathin films of LSMO.