Parametric spin pumping into an antiferromagnetic insulator

We report the observation of spin transport through antiferromagnetic insulators using spin pumping driven by short-wavelength magnons. The short-wavelength magnons are excited by parametric pumping in a Pt/NiO/Y3Fe5O12 trilayer. The parametrically excited magnons in the Y3Fe5O12 layer inject a spin current into the NiO layer, which is detected electrically using the inverse spin Hall effect in the Pt layer. We found that the spin-pumping efficiency of the parametrically excited magnons in the Pt/NiO/Y3Fe5O12 film is nearly an order of magnitude smaller than that in the Pt/Y3Fe5O12 film. The suppression of the parametric spin-pumping efficiency induced by inserting the NiO layer is comparable to that of the FMR spin-pumping efficiency. We further found that the suppression of the spin-pumping efficiency due to the NiO insertion for the dipole-exchange magnons with the wave number of k∼103-104cm-1 is more significant than that for the exchange magnons with k∼105cm-1. This difference is attributed to two-magnon scattering and spin pinning due to antiferromagnetic grains in the NiO layer. These results provide insight into the understanding of the spin pumping into antiferromagnetic insulators.