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 2/3 Sr 1/3 MnO 3 (LSMO) films grown on SrTiO 3 (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.