Spatial control of functional properties via octahedral modulations in complex oxide superlattices

Abstract

Control of atomic structure, namely the topology of the corner-connected metal-oxygen octahedra, has emerged as an important route to tune the functional properties at oxide interfaces. Here we investigate isovalent manganite superlattices (SLs), [(La(0.7)Sr(0.3)MnO(3))n/(Eu(0.7)Sr(0.3)MnO(3))n] × m, as a route to spatial control over electronic bandwidth and ferromagnetism through the creation of octahedral superstructures. Electron energy loss spectroscopy confirms a uniform Mn valence state throughout the SLs. In contrast, the presence of modulations of the MnO(6) octahedral rotations along the growth direction commensurate with the SL period is revealed by scanning transmission electron microscopy and X-ray diffraction. We show that the Curie temperatures of the constituent materials can be systematically engineered via the octahedral superstructures leading to a modulated magnetization in samples where the SL period is larger than the interfacial octahedral coupling length scale, whereas a single magnetic transition is observed in the short-period SLs.

Interface-induced phenomena in magnetism

“…The short length scale for interfacial octahedral coupling can be exploited to induce new magnetic phenomena, distinct from strain-driven effects, not present in compositionally equivalent bulk counterparts. For example, the distance between interfaces in a series of isovalent (La 0.7 Sr 0.3 MnO 3 ) n /(Eu 0.7 Sr 0.3 MnO 3 ) n superlattices was tuned to be either greater than or less than the octahedral coupling length scale by changing n , leading to modulated or uniform octahedral and magnetic behavior [Moon et al ., 2014b]. …”

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

“…[1][2][3][4] Recently, the control of local atomic structure, in particular BO 6 octahedral distortions and rotations and A-site displacements, has emerged as a promising strategy for designing functional properties in perovskite films. [5][6][7][8] One example of structure-driven design in oxide heterostructures is the prediction of hybrid improper ferroelectricity in (A ′ BO 3 )/(ABO 3 ) superlattices where both A ′ BO 3 and ABO 3 are perovskites that exhibit the orthorhombic P bnm structure in bulk. [9][10][11][12] In such superlattices, the inequivalent displacements of the A and A ′ cations produce a ferrielectric state.…”

Research Update: Interface-engineered oxygen octahedral tilts in perovskite oxide heterostructures

“…[14][15][16][17][18][19][20][21] The recent development of annular bright-field (ABF) imaging in STEM allows for simultaneous mapping of both light and heavy elements [22][23][24] and makes it possible to visualize oxygen coordination environments in the heterostructures. 18,25,26 Fast multiple-image acquisition and drift correction techniques using a cross correlation of the images 27 have been also demonstrated to minimize the image distortions due to drifts in both the specimen and incident probe in STEM, and consequently, the atomic positions for all constituent atoms-including oxygen-can be determined with sub-Ångström precision.…”