Manipulation of spin-wave attenuation and polarization in antiferromagnets

The coexistence of a left-handed polarized spin wave (LPSW) and a right-handed polarized spin wave (RPSW) in antiferromagnets provides a scheme for designing novel magnonic devices. To do so, it is necessary to manipulate the attenuation and the polarization of the LPSW and RPSW separately. We address this issue by studying theoretically the effect of spin-transfer torques (STTs) and an external magnetic field on spin waves (SWs) propagating in antiferromagnets. We find that Slonczewski-type STT can increase the attenuation length of one of the SW modes and decrease that of the other, while Zhang-Li type STT enhances (or weakens) the attenuation of both the LPSW and the RPSW simultaneously. Using the combined effect of the two kinds of STTs or the STT and an external magnetic field, we demonstrate control of the LPSW and RPSW attenuations separately, thus we can manipulate the SW polarization. We further suggest a magnon spin filter that can filter out one of the SW modes and preserve the other, which generates a pure magnonic spin current in antiferromagnets.