We report the observation of both metallic and semiconducting behavior in epitaxial thin films of the metallic oxide CaRuO3 deposited under identical conditions. X-ray diffraction studies showed that while semiconducting films with enlarged unit cells were obtained on single-crystal (100) SrTiO3 substrates, metallic films with lattice parameters close to the bulk material grew on (100) LaAlO3 substrates and poor crystalline quality SrTiO3 substrates. It is believed that a strain induced substitution of the small Ru4+ cations by the larger Ca2+ cations occurs, breaking the conduction pathway within the three-dimensional network of the RuO6 octahedra and leading to a metal–insulator transition. This unique phenomenon, which is not observed in bulk material, can be significant in technologically important epitaxial perovskite oxide heterostructures.
The magnetoresistance of epitaxial thin films (250 to 1000 A thick) of the metallic oxide ferromagnet SrRuO3 has been measured at temperatures ranging from well below to just above the Curie point ( = 160 K). Measurements using both transverse (nonzero Lorentz force) and longitudinal (zero Lorentz force) geometries cleanly distinguish between an orbital contribution, present only at low temperature, and a spin-Rip scattering contribution, present at all temperatures, to the resistivity in magnetic field. The magnetoresistance also shows strongly hysteretic behavior with high coercive and saturation fields. Through the Curie point, the magnetoresistance magnitude shows a maximum, which results from the suppression of the phase transition in magnetic field. The temperature derivative of the zero-field resistivity also shows a discontinuous jump, as predicted by standard theory.
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