Strain-Controlled Atomic Scale Distortions and Anti-Ferromagnetism at LaFeO₃/SrTiO₃ Interface

We present the strain-induced atomic-scale modification of magnetic canting in antiferromagnetic insulator LaFeO₃, which was investigated using high-precision imaging and diffraction in scanning transmission electron microscopy (STEM). Antiferromagnetic insulators have gained attention due to their low loss, fast switching, and potential for the next generation of spintronics applications. To advance this class of materials, we aim to acquire a precise understanding and control of how magnetic properties change with external stimuli, such as epitaxial strain. High-quality LaFeO₃ thin films were grown on [001] SrTiO₃ under in-plane compressive strain with ultrahigh vacuum off-axis sputtering. Superconducting quantum inference device magnetometry revealed increased net moment with decreasing film thickness, with the first few layers of the film having a larger magnetic moment (0.23 µB/Fe) relative to bulk (0.01 µB/Fe). We trace the structural origin of this change in magnetism to the changes in the lattice distortion at the interface. Atomic-scale STEM images show that the rotation of Fe-O octahedra changes within the first ~ 5 orthorhombic unit cells, with both the in-plane and out-of-plane rotations, progressively decreasing near the interface. Cation (La) positions are also affected by the strain at the interface, showing less distortion due to the connection to the cubic SrTiO₃. Nanoscale structural domains were also observed, and they are connected to the formation of magnetic domains near the interface, which we directly image using Lorentz TEM. Based on the experimental results, density functional theory calculation is performed to help elucidate the exact mechanism of the observed structure-property relationship. Our current study provides an atomic-level understanding of fast, efficient tuning of the magnetic states that is essential to advancing next-generation spin-electronics.