Strain Relief and Domain Architecture in Epitaxial NiO Films on La2/3Sr1/3MnO3/SrTiO3 for Spin-Transport Engineering

This study reports on the epitaxial growth and structural characterization of ultrathin NiO-films deposited by magnetron sputtering on La_2/3Sr_1/3MnO₃ (LSMO) films grown on SrTiO₃ (STO) substrates with (001)- and (111)-orientations. X-ray diffraction and atomic-force microscopy show that all NiO layers are single-phase, face-centered pseudo-cubic, atomically smooth, root-main-square (RMS) surface roughness <0.15 nm, and form abrupt interfaces with LSMO. High-resolution reciprocal-space maps reveal that the films are largely relaxed, but exhibit a slight compressive distortion, yielding unit-cell volumes larger than bulk NiO. Despite a nominal ≈7% lattice mismatch, aberration-corrected scanning transmission electron microscopy uncovers an array of misfit dislocations at the NiO/LSMO interface that help to accommodate strain allowing epitaxial growth of NiO layers. On (001)-oriented samples, the four antiferromagnetic T-domains are oblique to the sample plane, while on the (111) case, one lies in-plane. This in-plane domain shows greater spacing between ferromagnetic (111) planes due to unit cell distortion. This structural domain splitting can influence magnetic order and spin transmission efficiency, highlighting crystallographic orientation as a key factor in designing high-performance spintronic devices.