Strain effect on transport properties of SrRuO3 films grown by laser MBE

Transport properties of SrRuO3 thin films were studied as a function of the epitaxial strain. SrRuO3 films were grown on (100) SrTiO3 substrates by the Pulsed Laser Deposition technique equipped with Reflection High Energy Electrons Diffraction (RHEED). Samples thickness has been varied from a few unit cells to above 1000 Å while monitoring RHEED intensity oscillations. In thicker films epitaxial strain was found to be progressively relaxed. SrRuO3 relaxed films (thickness ≳ 1000 Å) show metallic behavior for the whole temperature range with a ferromagnetic ordering at about 150 K. For thinner films, ferromagnetic ordering occurs at progressively lower temperatures, until in films thinner than 400 Å it disappears. Films thinner than 80 Å show a semiconducting behavior at low temperatures. Our results provide direct evidence of the crucial role of the strain effect for conducting and magnetic properties of SrRuO3.