Interface-induced magnetic anisotropy inflected by CoN in AlN/Co/AlN heterostructure thinfilm

This study explores the correlation between interfacial chemistry and magnetic anisotropy in AlN/Co/AlN heterostructures with Co thicknesses of 3 nm (S1) and 12 nm (S2). Vibrating sample magnetometry reveals thickness-dependent behavior: ultrathin S1 exhibits strong in-plane magnetic anisotropy with exceptionally high coercivity (∼3400 Oe) as-deposited, while thicker S2 shows soft magnetic behavior (H c ∼ 70 Oe). Upon annealing at 300 °C and 400 °C, S1 transforms to metallic Co through nitrogen desorption with dramatically reduced coercivity (∼100 Oe), whereas S2 experiences decreased saturation magnetization and increased coercivity, indicating interfacial CoN formation. Polarization-dependent X-ray absorption fine structure spectroscopy with wavelet transform analysis provides atomic-scale evidence: S1 shows Co–N coordination (40%) as-deposited that vanishes after annealing, while S2 develops substantial Co–N bonding (70%) upon annealing. Magneto-optical Kerr effect measurements confirm strong uniaxial anisotropy in as-deposited S2, with annealing emergence of hard-axis anomalies (remanence peaks at 90°/270°) and multi-domain states, successfully described by the two-phase Stoner-Wohlfarth model. These results establish thickness-dependent nitrogen diffusion: ultrathin films favor desorption-driven metallic recovery, while thicker Co layer trap nitrogen at Co/AlN interfaces. This work provides insights for engineering thermally stable Co/nitride spintronic heterostructures with tunable anisotropy. • Annealing-controlled nitrogen diffusion in AlN/Co/AlN heterostructures enables functional magnetic property engineering. • Ultrathin Co (3 nm) recovers metallic ferromagnetism via nitrogen desorption, while thick Co (12 nm) forms interfacial nitrides suppressing magnetization. • Interfacial Co–N bonding induces exceptional coercivity (3400 Oe), creating opportunities for thermally tunable devices, semi-permanent magnets, and reconfigurable spintronic components with designer anisotropy.