Abstract
We investigate structural and transport properties of highly Ru-deficient SrRu0.7O3 thin films prepared by molecular beam epitaxy on (001) SrTiO3 substrates. To distinguish the influence of the two types of disorders in the films—Ru vacancies within lattices and disorders near the interface—SrRu0.7O3 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 SrRu0.7O3 thin films is as high as that of the ultrahigh-quality SrRuO3 ones. The Curie temperature (TC) analysis elucidated that SrRu0.7O3 (TC ≈ 140 K) is a material distinct from SrRuO3 (TC ≈ 150 K). Despite the large Ru deficiency (∼30%), the SrRu0.7O3 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 SrRu0.7O3 thin films irrespective of thickness, which is in contrast to the stoichiometric SrRuO3 films. The (magneto)transport properties suggest that a picture of carrier scattering due to the Ru vacancies is appropriate for SrRu0.7O3 and also that proper stoichiometry control is a prerequisite to utilizing the full potential of SrRuO3 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 SrRu1−xO3 is used as an epitaxial conducting layer.
Highlights
Interest in SrRuO3 has been further boosted by the observation of Weyl fermions18,19 and the realization of two-dimensional ferromagnetism in electrically conducting layers of one-unit-cell thickness embedded in [(SrRuO3)1/(SrTiO3)n] heterostructures
These intriguing phenomena are observed only in samples of exceptionally high quality,18,20 in those with a high residual resistivity ratio (RRR), which is known to be a good indicator of the purity of metallic systems
We investigated the structural and transport properties of highly Ru-deficient SrRu0.7O3 thin films prepared by molecular beam epitaxy (MBE) on (001) SrTiO3 substrates and compared the results to those of stoichiometric SrRuO3 thin films
Summary
The itinerant 4d ferromagnetic perovskite SrRuO3 has attracted strong attention because of the unique nature of its ferromagnetism, metallicity, chemical stability, and compatibility with other perovskite-structured oxides. It has been widely used in oxide electronics and spintronics as an epitaxial conducting layer. Recently, interest in SrRuO3 has been further boosted by the observation of Weyl fermions and the realization of two-dimensional ferromagnetism in electrically conducting layers of one-unit-cell thickness embedded in [(SrRuO3)1/(SrTiO3)n] heterostructures. These intriguing phenomena are observed only in samples of exceptionally high quality, in those with a high residual resistivity ratio (RRR), which is known to be a good indicator of the purity of metallic systems.. Interest in SrRuO3 has been further boosted by the observation of Weyl fermions and the realization of two-dimensional ferromagnetism in electrically conducting layers of one-unit-cell thickness embedded in [(SrRuO3)1/(SrTiO3)n] heterostructures.. Interest in SrRuO3 has been further boosted by the observation of Weyl fermions and the realization of two-dimensional ferromagnetism in electrically conducting layers of one-unit-cell thickness embedded in [(SrRuO3)1/(SrTiO3)n] heterostructures.20,21 These intriguing phenomena are observed only in samples of exceptionally high quality, in those with a high residual resistivity ratio (RRR), which is known to be a good indicator of the purity of metallic systems.. A promising approach to gain insight into the interfaces is to investigate thickness-dependent (magneto)transport properties of SrRuO3 films, especially down to the nanometer scale. The magnetization was measured with a Quantum Design MPMS3 SQUID-VSM magnetometer
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