Effect of the magnetic film thickness on the enhancement of the spin current by multi-magnon processes

We study experimentally the spin-current generation in yttrium iron garnet (YIG)/Pt bilayers based on YIG films with different thicknesses. Our results show that for all films with thicknesses exceeding a certain value, the spin current in the YIG/Pt system is enhanced at low frequencies. The cut-off frequencies, at which the enhancement starts, as well as the efficiency of the enhancement were found to increase with increasing film thickness. Good correlation between the cut-off frequency and the frequency at which the three-magnon splitting becomes allowed was observed. These findings prove that the latter process is responsible for the spin-current enhancement.