Ultrasonic spin pumping in the antiferromagnetic acoustic resonator $α-\text{Fe}_2\text{O}_3$

Abstract: Recent advances in magnon spintronics have ignited interest in the interactions between the spin and elastic subsystems of magnetic materials. These interactions suggest a dynamic connection between collective excitations of spins, quantized as magnons, and elastic waves generated by perturbations in the crystal lattice, quantized as phonons. Both magnons and their associated magnon-phonon excitations can act as sources of spin pumping from magnetic materials into non-magnetic metals. Although a considerable body of research has focused on spin pumping via elastic waves in ferromagnets, similar investigations involving antiferromagnets have yet to be undertaken. In this work, we experimentally demonstrate for the first time the feasibility of generating spin currents at ultrasonic frequencies of acoustic resonance in antiferromagnetic crystal hematite $\alpha-\text{Fe}_2\text{O}_3$ at room temperature. We provide both theoretical and experimental evidence that, due to strong magnetoelastic coupling, acoustic vibrations in hematite induce significant variable deviations in magnetization, resulting in spin accumulation at the antiferromagnet-normal metal interface, which in turn leads to the generation of spin and charge currents in the metal. Charge currents arising from the inverse spin Hall effect can be measured using the same methodology employed under high-frequency spin pumping conditions at the resonances of the magnetic subsystem itself. Moreover, the acoustic resonance in hematite is significantly more pronounced (by hundreds or even thousands of times) than in other quasiferromagnetic or antiferromagnetic systems, enabling the attainment of extremely large amplitudes of magnetic oscillations for spin pumping. This research highlights the new approach of utilizing acoustic spin pumping to manipulate spin currents in magnetic materials, particularly antiferromagnets.