Spin Dissipation Independent of Antiferromagnetic Order in IrMn

We investigate the interaction of spin current with antiferromagnetic order in polycrystalline IrMn by resonant spin pumping. We use spin-valve-like multilayers (NiFe/Cu/IrMn/CoFe), in which no direct magnon coupling is present between the NiFe spin source and the exchange-biased IrMn/CoFe spin sink; the pumped pure spin current is mediated solely by electrons through the Cu spacer layer. We observe no anisotropic spin dissipation with respect to the exchange bias direction, nor do we observe any difference in spin dissipation for samples with and without pinned antiferromagnetic order. Moreover, although there is a pronounced resonance linewidth increase in NiFe that coincides with the switching of IrMn/CoFe, we show that this is not indicative of anisotropic spin dissipation in IrMn. Our results demonstrate that the dissipation of electron-mediated spin current is remarkably insensitive to the magnetization state of the antiferromagnetic IrMn spin sink.