Octahedral rotation patterns in strainedEuFeO3and otherPbnmperovskite films: Implications for hybrid improper ferroelectricity

Abstract

We report the relationship between epitaxial strain and the crystallographic orientation of the inphase rotation axis and A-site displacements in P bnm-type perovskite films. Synchrotron diffraction measurements of EuFeO3 films under strain states ranging from 2 % compressive to 0.9 % tensile on cubic or rhombohedral substrates exhibit a combination of a − a + c − and a + a − c − rotational patterns. We compare the EuFeO3 behavior with previously reported experimental and theoretical work on strained P bnm-type films on non-orthorhombic substrates, as well as additional measurements from LaGaO3, LaFeO3, and Eu0.7Sr0.3MnO3 films on SrTiO3. Compiling the results from various material systems reveals a general strain dependence in which compressive strain strongly favors a − a + c − and a + a − c − rotation patterns and tensile strain weakly favors a − a − c + structures. In contrast, EuFeO3 films grown on P bnm-type GdScO3 under 2.3 % tensile strain take on a uniform a − a + c − rotation pattern imprinted from the substrate, despite strain energy considerations that favor the a − a − c + pattern. These results point to the use of substrate imprinting as a more robust route than strain for tuning the crystallographic orientations of the octahedral rotations and A-site displacements needed to realize rotation-induced hybrid improper ferroelectricity in oxide heterostructures.

Semi-Dirac and Weyl Fermions in Transition Metal Oxides

“…Particularly, the Berry curvature and the resulting anomalous Hall conductivity vary non-monotonically with increasing θ. Previous experiments have demonstrated that external strain modulation can control octahedral rotations in oxide thin films [43,44]. Our presented results, therefore, show an effective way to control the Berry phase and consequently the topological properties of perovskite transition-metal oxides by epitaxial strain engineering.…”

Impact of interfacial coupling of oxygen octahedra on ferromagnetic order in La0.7Sr0.3MnO3/SrTiO3 heterostructures

“…These atomic density changes boost the enhancement of the relative oxygen/cation contrast; therefore, under the premise of high spatial resolution in a Cs-corrected STEM, the <110> pc zone axis provides a better contrast of the oxygen columns than the <100> pc zone axis. Moreover, considering the characteristics of in-plane oxygen octahedral rotation, such as in the case of a − a − c + (following Glazer’s notation41) in orthorhombic LSMO (space group Pnma )42, the anti-phase rotation in the <100> pc zone axis introduces a split of the oxygen columns, thus blurring and eclipsing the oxygen atomic propagation, while the in-phase rotation in the [1–10] pc zone axis gives a sharp propagation. Accordingly, the [1–10] pc zone axis was selected in our work for an enhanced contrast of the oxygen and in-phase octahedral rotation in each LSMO monolayer of the heterostructures (a detailed quantitative ABF intensity analysis can be found in the supporting information Figure S2).…”

Negative magnetoresistance in epitaxial films of neodymium nickelate

“…Additionally, there is a symmetry misfit arising from NiO 6 -octahedral tilts (rotations) in NNO. Such a symmetry misfit is typical for the epitaxy of orthorhombic perovskites on square surfaces of versatile substrates [10][11][12][13]. The symmetry misfit relaxes within a few nanometers near the film-substrate interface, as was evidenced by the evolution of tilts towards bulklike patterns in nickelates [11,[14][15][16].…”