F. Rödelsperger

Chaotic Dynamics in Spin-Wave Instabilities

Ferromagnetic samples excited by strong microwave fields show a variety of nonlinear phenomena. We report on magnetic resonance experiments in yttrium iron garnet (YIG) probing spin-wave instabilities above the first-order Suhl threshold. A very complex multistable behaviour and various types of auto-oscillations and sequences of bifurcations are observed, ending up in chaos. The experimental behaviour can be interpreted in terms of a multimode-model taking into account both spin waves and magnetostatic modes.

Different types of intermittency observed in transverse-pumped spin-wave instabilities

Abstract 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.

Delayed bifurcations at the first-order Suhl threshold

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.

Route out of chaos by HF parametric perturbations in spin-wave instabilities

Abstract 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.

Multistability and Chaos in Transverse-Pumped Spin-Wave Instabilities

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.