Spin-orbit torque-driven synthetic antiferromagnetic oscillator

Antiferromagnets offer a promising route toward robust spintronic devices because of their compensated magnetic order and exchange-enhanced spin dynamics. Here, we demonstrate a spin-orbit torque (SOT)-driven antiferromagnetic oscillator based on a nanoconstriction patterned from a synthetic antiferromagnet (SAF). Spin-rectification spectroscopy reveals electrical excitation of both acoustic and optical SAF eigenmodes, whose field and frequency dependences are quantitatively described by an antiferromagnetic resonance model. In addition to these linear eigenmodes, we observe low-field spin-rectification peaks that emerge only above a threshold DC current near the spin-flop transition. Their current-polarity-dependent sign and locking to an injected RF frequency provide electrical spin-rectification signatures consistent with current-selected chiral self-oscillatory dynamics. Micromagnetic simulations reproduce the threshold excitation of SOT-driven self-oscillations and injection locking, while macrospin simulations predict stable and chaotic nonlinear dynamics within the same spin-flop region. We interpret the multi-peak, weakly RF-frequency-dependent responses as a qualitative signature of complex nonlinear dynamics. These results establish SAF nanoconstrictions as an experimentally accessible platform for studying current-driven antiferromagnetic-like oscillator dynamics and motivate future work on nonlinear spintronic devices for signal processing and reservoir-computing concepts.