MEASUREMENT OF SPIN-WAVE INSTABILITY MAGNON DISTRIBUTIONS FOR SUBSIDIARY ABSORPTION IN YTTRIUM-IRON-GARNET FILMS BY BRILLOUIN LIGHT-SCATTERING

The first evidence for a wide distribution in the critical mode wave v ectors above the spin wave instability threshold for subsidiary absorp tion is reported. The Brillouin light scattering (BLS) measurements we re done on 4.15 mum thick yttrium iron garnet films with the static fi eld and the 8.47 GHz linearly polarized microwave field in plane. The distribution in the critical mode wave number is broad, with widths of about 0.5 x 10(4)-2 x 10(4) cm-1 and shapes which change with field a nd power. These results cast doubts on,the validity of simple two mode models for the analysis of self-oscillation, chaos, and related effec ts above threshold.