Controlling Antiferromagnetic Magnon Polarization by Interfacial Exchange Interaction

Abstract

We demonstrate highly efficient control of antiferromagnetic (AFM) magnon spins by the interfacial exchange interaction in heterostructures of ferrimagnetic yttrium iron garnet (YIG) and AFM ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$. At low temperatures, ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ is antiferromagnetically ordered. The interfacial exchange interaction exerted by YIG lifts the degeneracy between the AFM magnon modes in ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, resulting in a net spin polarization and a spin current dominated by left-handed magnons, even at zero magnetic field, which is detected by the spin Seebeck effect with a 5-nm-thick $\mathrm{Pt}$ film. In the AFM magnon-dominated region, even if the magnetic field is not sufficiently strong to induce the spin-flop transition in ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, the total spin Seebeck signal polarity flips when the YIG magnetization switches. It clearly indicates that the ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ magnon polarization is controlled by YIG magnetization through the interfacial exchange interaction. The demonstration of the efficient control of AFM magnon polarization opens a pathway to manipulate AFM magnon quantum states using FM-AFM heterostructures.