A schematic of the octahedral rotations and tilts in the perovskite structure. The rotation angle is given by (90°-Ω)/2, whereas the tilt angle is defined as (180°-θ)/2. Octahedral rotation is along the z axis, whereas tilt is along the x and y axes.
Normalized Ru K-edge XANES of Ru metal standard (black dotted curve), and SRO films grown in 100 mTorr (blue solid curve) and 30 mTorr (red dashed curve) oxygen. The shift of absorption edge to high energy at Ru K-edge of SRO film grown in 100 mTorr oxygen indicates that the oxidation state of Ru is higher than that of SRO film grown in 30 mTorr oxygen. Inset is the XANES spectra in a wider x-ray energy range.
(a) and (b) RSMs of SRO films grown in (a) 100 mTorr and (b) 30 mTorr on STO substrates. SRO film grown in 100 mTorr clearly shows a pseudo-orthorhombic unit cell with ao ≠ bo , while SRO grown in 30 mTorr shows a tetragonal unit cell with ao = bo . Here, we used , where θ is the Bragg angle and λ = 1.540598 Å. (c) The orthorhombicity factor ao /bo as a function of the oxygen partial pressure (PO2) at which the SRO films were deposited. The abrupt change of ao /bo from ∼1.007 to unity indicates a structural phase transition from pseudo-orthorhombic to tetragonal structure at a PO2 in a range from 60 mTorr to 45 mTorr.
Schematic representation of two possible epitaxial relationships of tetragonal SRO films and STO substrates. (a) SRO film is (110)o-oriented with c o in the film plane. (b) SRO film is of (001)o orientation with c o perpendicular to the film surface.
(a) and (b) Schematic top view of RuO6 octahedral tilts in SRO thin films of (a) pseudo-orthorhombic phase and (b) tetragonal phase. (c) and (d) Magnetic hysteresis loops measured at 5 K along three principle axes. (e) and (f) Temperature dependence of magnetization curve taken after field-cooled from room temperature with the application of a magnetic field of 100 Oe. (c) and (e) are for the SRO film grown in 60 mTorr, (d) and (f) are for the ones grown in 30 mTorr oxygen.
A schematic view of the orbital overlap between Ru1 and Ru2 ions along y axis. The dxz orbital is colored red, the dxy orbital green, and the dyz orbital blue. The octahedral rotation along y axis is in-phase in (a) and out-of-phase in (b).
The simple geometrical view of the RuO6 octahedra in (a) pseudo-orthorhombic SRO phase with octahedral tilts and (b) tetragonal SRO phase without octahedral tilts. The Ru-O-Ru bond angle θ along the z-axis is approaching 180° for the tetragonal phase. (c) and (d) Energy splitting diagram of Ru 4 d orbitals in the presence of an octahedral field (c) before and (d) after taking away one oxygen atom at the O(1) site.
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