Brillouin light scattering study of spin wave instability magnon distributions in yttrium iron garnet thin films (abstract)

Abstract

There has been increased interest recently in nonlinear microwave phenomena in bulk and thin film single crystal ferrite materials. These nonlinear phenomena show a variety of novel effects such as spin wave instability, auto-oscillation, multistability, period multiplication, intermittency, and chaos. Emerging theories to explain these phenomena have generally been based on simple two mode models. It is clear that an experimental determination of the number and distribution of the modes excited at and above the spin wave instability threshold could play a key role in the refinement of these theories. This work is concerned with a Brillouin light scattering (BLS) experimental study of the wave vector distribution of the parametric spin wave modes excited at and above the subsidiary absorption spin wave instability threshold in yttrium iron garnet (YIG) films. The in-plane magnetized 4.15-μm-thick films were transverse pumped at 8.47 GHz, with the microwave field also in-plane. The BLS data were obtained with a tandem, multipassed, high contrast Sandercock Fabry–Perot interferometer. The data show a complicated wave vector distribution for the excited modes. The spin wave propagation direction is sharply peaked at the value expected from standard instability theory. However, the wave number distribution is quite broad, even at threshold. For power levels above threshold, this distribution evolves in a complicated manner that depends on field and propagation direction. These results show that simple two mode models are inadequate to deal with high frequency nonlinear processes in ferrite thin films.