Birefringence-like spin transport via linearly polarized antiferromagnetic magnons

Antiferromagnets (AFMs) possess great potential in spintronics because of their immunity to external magnetic disturbance, the absence of a stray field or the resonance in the terahertz range^1,2. The coupling of insulating AFMs to spin-orbit materials^3-7 enables spin transport via AFM magnons. In particular, spin transmission over several micrometres occurs in some AFMs with easy-axis anisotropy^8,9. Easy-plane AFMs with two orthogonal, linearly polarized magnon eigenmodes own unique advantages for low-energy control of ultrafast magnetic dynamics². However, it is commonly conceived that these magnon modes are less likely to transmit spins because of their vanishing angular momentum^9-11. Here we report experimental evidence that an easy-plane insulating AFM, an α-Fe₂O₃ thin film, can efficiently transmit spins over micrometre distances. The spin decay length shows an unconventional temperature dependence that cannot be captured considering solely thermal magnon scatterings. We interpret our observations in terms of an interference of two linearly polarized, propagating magnons in analogy to the birefringence effect in optics. Furthermore, our devices can realize a bi-stable spin-current switch with a 100% on/off ratio under zero remnant magnetic field. These findings provide additional tools for non-volatile, low-field control of spin transport in AFM systems.