Spin-filter tunneling detection of antiferromagnetic resonance with electrically-tunable damping

We demonstrate spin-filter tunneling detection of antiferromagnetic resonance (AFMR) in bilayer CrSBr using a scalable, three-terminal device geometry. CrSBr exhibits strong in-plane triaxial anisotropy and supports multiple gigahertz AFMR modes depending on field orientation, including hybridized chiral, out-of-phase and in-phase modes. By rotating the external magnetic field away from high symmetry axes, we access mode hybridization and multiaxial dynamics.

 

To achieve electrical readout, we adapt spin-torque ferromagnetic resonance (ST-FMR) techniques using the c-axis tunneling magnetoresistance of CrSBr, which is sensitive to the relative orientation of spin sublattices. AFMR modes are excited via an RF current, and their dynamics are detected through rectified voltages measured with a lock-in amplifier as the field is swept across resonance. The technique enables detection in micron-scale devices, over 1000× smaller than previously possible, and reveals suppressed interlayer exchange in thin CrSBr relative to the bulk.

 

Beyond passive detection, our geometry allows active electrical control of AFMR damping. By injecting a dc current through a PtTe₂ electrode, we apply spin-orbit torque (SOT) to tune the linewidth of the optical mode. A two-sublattice analysis shows that the damping scales linearly with drive current when the spin polarization aligns with one of the canted sublattices. We extract a damping-like SOT efficiency of ξ = 0.29(2), comparable to known ferromagnetic systems. Strikingly, we observe an asymmetry in the linewidth modulation under positive and negative magnetic fields, consistent with a localized SOT picture where the torque acts only on the sublattice directly adjacent to the PtTe₂ electrode. Our results contribute to extending the capabilities of SOT devices using the properties of antiferromagnets distinct from conventional ferromagnetic heterostructures. This opens new approaches to controlling layered antiferromagnets and provides a strategy for utilizing antiferromagnetic materials in high frequency applications.