Strange attractor of controlled chaos in yttrium iron garnet films

Parametrically excited spin waves in an yttrium iron garnet (YIG) are good model objects to study nonlinear dynamics. Chaotic oscillations of this sys tem can be controlled with a time-delayed feedback method. The feedback per turbation was added to the static magnetic field. This controlling process has been characterized by strange attractors. With increasing feedback gain , a fractal dimension of the strange attractor decreases from 2.9 to 1.1. T his means that chaotic oscillations change to periodic oscillations success ively. Further increase of feedback gain eventually produces chaotic oscill ations again.