Self-organized in-plane ordering of nanostructures at epitaxial ferroelectric–ferromagnetic interfaces

Abstract

The formation of self‐assembled structures is of great interest in the field of ferroelectric (FE)–ferromagnetic (FM) oxide interfaces with novel functionalities driven by the combination of strain relaxation and diffusion/segregation processes occurring during epitaxial growth of Mn‐based heterostructures. In epitaxial bilayers and multilayers of La0.67Sr0.33MnO3 (LSMO)/BaTiO3 (BTO) on (001) SrTiO3, using the grazing‐incidence small‐angle X‐ray scattering technique, self‐assembled in‐plane structural ordering with a repeated sequence of the bilayers has been found. This ordering has important magnetic consequences, as the materials show characteristics of a superparamagnetic type of behavior even with an increased number of bilayers. Transmission electron microscopy images reveal strain due to lattice mismatch between BTO and LSMO. This strain is greatly enhanced with the number of BTO and LSMO repetitions in a multilayer as an interdiffused columnar structure is formed. Electron energy loss spectra indicate a variation in oxygen environment from one monolayer to another within one LSMO layer. Reflectivity measurements with polarized neutrons prove that the LSMO layers are grown with sufficient periodicity but have a strongly reduced magnetic moment. This reduction is plausibly associated with interfacial strain and varying oxygen deficiencies within the layers or symmetry breaking effects which can turn the LSMO layer almost antiferromagnetic.

Atomic-scale engineering of ferroelectric-ferromagnetic interfaces of epitaxial perovskite films for functional properties

“…One may note that a full strain relaxation typically occurs above a thickness of 100 nm. Initial sample characterizations 11 were done using X-ray reflectivity (XRR) and X-ray diffraction (XRD) and has been shown in the supplementary section.…”

Tiling the Silicon for Added Functionality: PLD Growth of Highly Crystalline STO and PZT on Graphene Oxide-Buffered Silicon Surface

“…The “remote” heteroepitaxy, as an alternative approach to the direct heteroepitaxy, has been recently reported, where a graphene interlayer partially screens the substrate electrostatic potential, reduces the nucleation rate, and simultaneously promotes the growth of the epilayer. − It is demonstrated that the amount of energetically favorable dislocations for relaxing the lattice strain, which primarily results from a lattice mismatch between the overgrown layer and the host substrate, can be largely reduced thanks to two-dimensional (2D) materials that alleviate the interaction when the graphene-coated substrate was used for epitaxy. , In this regard, epitaxial III–V materials with low-density defects have been successfully grown on top of mono- or bilayer graphene-coated substrates, followed by exfoliation and transfer onto the target substrate to produce high-quality devices. , In such cases, the self-organized in-plane ordering of nanostructures has been found to be important for various functional heterostructures . On the other hand, complex-oxide materials showing extensive functionalities including ferromagnetism, ferroelectricity, and piezoelectricity have also been explored to realize epitaxial growth on graphene-buffered substrates. , For example, Kum et al demonstrated high-quality single-crystalline BaTiO 3 (BTO) and SrTiO 3 (STO) epilayers grown on graphene-coated STO substrates .…”

“… 24 , 25 In such cases, the self-organized in-plane ordering of nanostructures has been found to be important for various functional heterostructures. 26 On the other hand, complex-oxide materials showing extensive functionalities including ferromagnetism, ferroelectricity, and piezoelectricity have also been explored to realize epitaxial growth on graphene-buffered substrates. 22 , 27 For example, Kum et al demonstrated high-quality single-crystalline BaTiO 3 (BTO) and SrTiO 3 (STO) epilayers grown on graphene-coated STO substrates.…”