Spin pumping without three-magnon splitting in polycrystalline Bi ₁Y ₂Fe ₅O ₁₂/Pt bilayer structure

Spin pumping at various precession frequencies has been investigated in a polycrystalline Bi-substituted yttrium iron garnet (Bi.YIG)/Pt bilayer structure by means of inverse spin Hall effect (ISHE) with comparison to a single crystal La-substituted yttrium iron garnet (La.YIG)/Pt bilayer structure which shows three-magnon splitting. As precession frequency decreases, the magnitude of pumped spin currents in the polycrystalline sample continuously increases to high magnitude comparable to the highest magnitude in the single crystal sample while that in the single crystal sample decreases below a threshold frequency of three-magnon splitting. By comparing ISHE voltage with microwave absorption intensity in the polycrystalline sample, we verify that the large magnitude of the pumped spin currents is maintained at low frequencies through the suppression of three-magnon splitting.