Sub-terahertz bimodal spin pumping in bulk and thin film heterostructures of canted antiferromagnetic α-Fe₂O₃/Pt at room temperature

Hematite is an insulating easy-plane antiferromagnet which exhibits a room temperature canted phase induced by the super-exchange Dzyaloshinskii--Moriya Interaction (DMI), boasting resonances in the sub-terahertz range with enhanced spin pumping and spin transport over its uniaxial counterparts. In this work we magnetically probe the acoustic and optical modes of antiferromagnetic heterostructures α-Fe2O3/Pt(5nm) across different thicknesses of the antiferromagnetic layer using a polarization- tunable free-space microwave system at sub-terahertz frequencies. For bulk hematite, coherently pumped spin currents and resultant charge rectification are observed across the entire magnetic landscape, producing a complete field-frequency mapping of the acoustic and optical spin dynamical modes of the system. We obtain measures for the Gilbert damping in both modes and the DMI field in good agreement with literature. By altering the polarization state of the microwaves, selectively excited dynamics demonstrate spin-to-charge conversion out of the optical mode of this spin canted system , further developing the understanding of canted antiferromagnets and their potential use in next generation terahertz oscillators. Furthermore, we observe resonant spin pumping from a thin-film antiferromagnetic heterostructure α-Fe2O3(30nm)/Pt(5nm) up to 170 GHz. Inverse Spin-Hall Voltages are produced on the same scale as the system’s bulk counterpart, providing initial evidence for the efficacy of nanoscale insulating antiferromagnets as THz magnetic devices hosting high-frequency spin-to-charge conversion.