Two-Magnon Scattering Enhanced by Randomly-Distributed Antiferromagnetic Exchange Field

We report a quantitative study of two-magnon scattering in Ni₈₁Fe₁₉/NiO bilayers with various NiO thicknesses. The magnetic damping of the Ni₈₁Fe₁₉/NiO bilayer was found to have strong dependence on NiO thickness. The amplitude of the two-magnon scattering is enhanced with increasing the thickness of the antiferromagnetic layer, which was evaluated from the out-of-plane-angular-dependent spectral linewidth of ferromagnetic resonance. The origin of this enhancement in the Ni₈₁Fe₁₉/NiO bilayer is the increase of randomly-distributed antiferromagnetic exchange fields. We have calculated the spin-mixing conductance by eliminating the effect of the two-magnon scattering, and found that the value is at 8.1 nm^-2 for the Ni₈₁Fe₁₉/NiO interface. Skipping this process leads to overestimation of spin-mixing conductance in ferromagnet/antiferromagnet bilayer structures. 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 widely-studied ferromagnet/antiferromagnet systems.