Intrinsic Spin Decay Length In An Antiferromagnetic Insulator

We report intrinsic spin decay length of an antiferromagnetic insulator. We found that at an antiferromagnetic/ferromagnetic interface, a spin current generated by spin pumping is strongly suppressed by two-magnon scattering. By eliminating the two-magnon contribution, we discovered that the characteristic length of spin decay in polycrystalline NiO changes by two orders of magnitude through the paramagnetic to antiferromagnetic transition. The spin decay length in the antiferromagnetic state is around 100 nm, which is an order of magnitude longer than that previously believed. These results provide a crucial piece of information for the fundamental understanding of the physics of spin transport.