The dynamics of the magnetization of yttrium iron garnet spheres was studied by ferromagnetic resonance both within the subsidiary absorption regime and the coincidence regime of the first-order Suhl instability. The absorption signal shows auto-oscillations with a rich variety of nonlinear behavior. Along with other routes to chaos we observed intermittency and identified each of the Pomeau-Manneville types I-III. Within the chaotic regime crisis-induced intermittency, on-off intermittency, and noise-induced intermittent behavior were observed. [S1063-651X(99)00602-9].

In this paper, we present both theoretical and experimental analysis of delayed dynamic bifurcations as could be observed by ferromagnetic resonance (FMR) on an yttrium iron garnet (YIG) sphere. In Sec. 1 the static bifurcation behaviour of the first-order Suhl instability is analyzed in terms of a two-mode model, which represents the simplest possible description of this process. In Sec. 2 our analytical results are extended to the dynamic case by means of numerical simulations, including the influence of noise. We present our experimental results and compare them with the obtained theoretical predictions.

Chaotic behaviour of a nonlinear system can be suppressed by fast parametric modulation. Analytical and numerical investigations show that the increase of the modulation amplitude corresponds to an effective variation of the modulated parameter and results in a scenario ‘out of chaos’. Applying this method to a spin-wave experiment in YIG, the dynamics is changed from chaotic to periodic via type-III intermittency.

Dynamic instabilities of magnetization in YIG spheres were studied by high-power ferromagnetic resonance at the first-order Suhl instability. By means of an analog feedback technique implementing the controlling scheme of Ott, Grebogi and Yorke, we suppressed the chaotic FMR signal and stabilized a periodic oscillation by applying a very small time-dependent feedback signal of less than 10−3 of the applied microwave power.

The photothermally modulated (PM) ferromagnetic resonance (FMR) combines the high sensitivity of conventional FMR and spatial resolution.This technique has been applied to a single-crystalline yttrium iron garnet (YIG) sphere with a diameter of 2 mm.For the first time, the spatial variation of the high-frequency magnetization patterns known as Walker modes were visualized and it is thus shown that PM-FMR can even be applied to unfavourable geometries.

The dynamic behaviour of magnetization in YIG spheres was studied by FMR within the coincidence regime of the first-order Suhl instability. For certain ranges of the control parameters (magnetic field, microwave frequency and amplitude, etc.) the time-resolved absorption signal shows auto-oscillations changing over to chaos by intermettency. We clearly observed each of the types I–III and rather often crises.

Spin wave instabilities in YIG spheres have been studied by FMR within the coincidence regime of the first-order Suhl instability. A complex multistable behaviour is observed, resulting in various types of auto-oscillations, sequences of bifurcations, intermittency and chaos. Our experimental results are discussed in terms of a multimode-model considering both spin-waves and magnetostatic modes.