Structural and transport properties of highly Ru-deficient SrRu0.7O3 thin films prepared by molecular beam epitaxy: Comparison with stoichiometric SrRuO3

摘要

We investigate structural and transport properties of highly Ru-deficient SrRu 0.7 O 3 thin films prepared by molecular beam epitaxy on (001) SrTiO 3 substrates. To distinguish the influence of the two types of disorders in the films—Ru vacancies within lattices and disorders near the interface—SrRu 0.7 O 3 thin films with various thicknesses ( t = 1–60?nm) were prepared. It was found that the influence of the former dominates the electrical and magnetic properties when t ≥ 5–10?nm while that of the latter does when t ≤ 5–10?nm. Structural characterizations revealed that the crystallinity, in terms of the Sr and O sublattices, of SrRu 0.7 O 3 thin films is as high as that of the ultrahigh-quality SrRuO 3 ones. The Curie temperature ( T C ) analysis elucidated that SrRu 0.7 O 3 ( T C ≈ 140?K) is a material distinct from SrRuO 3 ( T C ≈ 150?K). Despite the large Ru deficiency (～30%), the SrRu 0.7 O 3 films showed metallic conduction when t ≥ 5?nm. In high-field magnetoresistance measurements, the fascinating phenomenon of Weyl fermion transport was not observed for the SrRu 0.7 O 3 thin films irrespective of thickness, which is in contrast to the stoichiometric SrRuO 3 films. The (magneto)transport properties suggest that a picture of carrier scattering due to the Ru vacancies is appropriate for SrRu 0.7 O 3 and also that proper stoichiometry control is a prerequisite to utilizing the full potential of SrRuO 3 as a magnetic Weyl semimetal and two-dimensional spin-polarized system. Nevertheless, the large tolerance in Ru composition (～30%) to metallic conduction is advantageous for some practical applications where SrRu 1? x O 3 is used as an epitaxial conducting layer.