Spin‐Selective Interface Engineering in Oxide–Ferromagnetic Junctions via Atomic‐Scale Oxygen Control

ABSTRACT Atomic‐scale control of oxide–ferromagnet interfaces is crucial for optimizing spintronic heterostructures, yet interfacial oxygen remains difficult to control and verify. Here, we deterministically tune the prototypical MgO/Fe(100) interface from oxygen‐free terminations to fully intercalated oxygen layers by reactive growth under controlled O2 exposure, while preserving epitaxy. Momentum‐resolved photoemission identifies oxygen‐dependent fingerprints in k‐space that originate from the buried interface and persist up to a thickness of 8 layers of MgO. Insights from complementary spectroscopic methods link these k‐space signatures to interfacial chemistry, structural order, work‐function shifts, and an oxygen‐induced interface resonance within the MgO gap that alters the tunneling response. The combined results define a calibrated growth protocol that allows reproducibly preparing and identifying three distinct terminations — oxygen‐free, partially oxidized, and oxygen‐intercalated — and enables post‐growth conversion even in thicker films. Complementary spin‐resolved experiments reveal that oxygen‐free interfaces exhibit pronounced suppression of minority‐spin spectral weight at the Fermi level, consistent with coherent spin filtering across crystalline MgO, whereas oxygen intercalation reduces the spin contrast at EF. By turning interfacial oxygen from an uncontrolled variable into a measurable, adjustable parameter, our approach establishes MgO/Fe(100) as a benchmark platform for optimizing spintronic functionality in oxide/metal junctions.