| Perovskite oxides, because of its complicated structure and fantastic properties, are the hot research field of condensed matter physics in recent years. Typical phenomena such as piezoelectric, ferroelectric, and magnetoresistance found in perovskite have broad application foreground, attracting a lot of attention in physics, material science, electronics, and industry. There is much interest in unveiling the mystic mechanism behind the rich physical phenomena in perovskite oxides. The strong couplings among lattice, spin, charge, and orbital degrees of freedom in transition perovskite oxides set up an arena for probing novel phenomena such as superconductivity, multiferroics, and giant Magnetoresistance. Therefore, understanding perovskite oxides is essential for research in functional material because it could lead to discovering new materials with advanced properties and unique functionality.In this paper, the transition perovskite oxides La2/3Sr1/3MnO3 and SrRuO3 have been taken as subjects. Using first principles calculations based on density functional theory, we investigate the interface properties of (La2/3Sr1/3MnO3)m/(SrRuO3)n superlattices and SrRuO3 with Ru-vacancy. Transition perovskite oxide La2/3Sr1/3MnO3, because of its higher Curie temperature of 370 K and half-metallic property, is a popular candidate in spintronics. But, with the decrease of film thickness, the Curie temperature of La2/3Sr1/3MnO3 decreases rapidly and even becomes antiferromagnetic insulator. On the other hand, the 4d itinerant ferromagnetic SrRuO3 shows strong signatures of glass behavior both in epitaxial films and bulk samples. Therefore, it is urgent to study the interface and deficient properties of these ferromagnetic metals. The main results are listing as following.(1) It is found that the properties (La2/3Sr1/3MnO3)m/(SrRuO3)n films are closely related with the homogeneity of La2/3Sr1/3O layer. An obvious Jahn-Teller distortion, which depends on m, n, appears in MnO6 octahedron in the superlattices. The stretch along c-axis of MnO6 octahedron at the interface lifts the Mn eg orbital degeneracy, with electrons preferring the lower energy 3z2-r2 to the higher energy x2-y2. Benefitting from the charge transfer at the interface, the still occupied x2-y2 orbital can mediate a robust in-plane double exchange interaction. La2/3Sr1/3MnO3 block is ferromagnetic and metallic, even for the superlattice with m=n=1. In the superlattices, there is a strong coupling between the charge transfer and the relaxation of structure. Microscopically, the shift of A-site ions toward MnO2 plane increases the electron density of MnO2 plane, strengthening the double exchange interaction between Mn ions. MnO6 octahedron is always distorted at the interface, but the results indicate that homogeneous La2/3Sr1/3O layer can reduce the distortion, enhancing the properties of films.(2) It is found that the Ru-vacancy has leads to antiferromagnetic clusters in SrRuO3 crystal. Substantial local structure relaxations occurred around the Ru vacancy site. Specifically, the nearest Ru and O ions of the vacancy move away from Ru-vacancy, while the nearest Sr ions shift toward the vacancy. Interesting, an antiferromagnetic spin cluster is formed in the vicinity of the Ru-deficient site. This, in turn, gives rise to reduced overall magnetic moment which agrees better with the experiment values for SrRuO3 reported in literature. The adjustment of O ions surrounding the vacancy splits the near-vacancy Ru t2g orbitals, and the unoccupied ones appear above the Fermi level. The truncated effect at the vacancy, modified Ru-O covalent bonds, and Ru-O-Ru angles which jointly stabilized the antiferromagnetic spin cluster. |
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