Atomically defined epitaxy and physical properties of strained La0.6Sr0.4MnO3 films

Abstract

${\mathrm{La}}_{\mathrm{0.6}}{\mathrm{Sr}}_{\mathrm{0.4}}{\mathrm{MnO}}_{\mathrm{3}}$ thin films were fabricated on ${\mathrm{SrTiO}}_{\mathrm{3}}$ (001) substrates using pulsed laser deposition with observing persistent intensity oscillation of reflection high-energy electron diffraction. By atomic force microscopy, the surface of resulting films was confirmed to be extremely flat, showing atomically smooth terraces and 0.4 nm high steps corresponding to a unit cell height of perovskite. The surface terminating atomic layer was unambiguously assigned to the ${\mathrm{MnO}}_{\mathrm{2}}$ layer by coaxial impact collision ion scattering spectroscopy. Crystal symmetry of the films is distorted into a tetragonal one due to the strain to fulfill perfect in-plane matching with the substrate even for films as thick as 100 nm. Even for films as thin as 4 nm (10 unit cells), ferromagnetic transition takes place to induce a metallic state and large negative magnetoresistance is observed as well.