Enhancement of two-magnon scattering induced by a randomly distributed antiferromagnetic exchange field

We report a quantitative study of two-magnon scattering in ${\mathrm{Ni}}₈₁{\mathrm{Fe}}₁₉$/NiO bilayers with various NiO thicknesses ${d}_{\mathrm{NiO}}$. We found that the magnetic damping of the ${\mathrm{Ni}}₈₁{\mathrm{Fe}}₁₉$/NiO bilayer strongly depends on ${d}_{\mathrm{NiO}}$, which evidences that the amplitude of the two-magnon scattering increases with increasing the thickness of the antiferromagnetic layer. The enhancement of the two-magnon scattering in the ${\mathrm{Ni}}₈₁{\mathrm{Fe}}₁₉$/NiO bilayer is attributed to the increase of randomly distributed antiferromagnetic exchange fields. We calculated the spin-mixing conductance by eliminating the effect of the two-magnon scattering, and found that the value is at $8.1\phantom{\rule{0.16em}{0ex}}{\mathrm{nm}}^{\ensuremath{-}2}$ for the ${\mathrm{Ni}}₈₁{\mathrm{Fe}}₁₉$/NiO interface. Our result gives further insight on the role of the two-magnon scattering in manipulating magnetic damping, which is crucial for generation and transmission of spin currents in ferromagnet/antiferromagnet systems.