Hartmut Benner
Chaos control in spin systems
Institut für Festkörperphysik, TU Darmstadt
Spin systems represent intriguing paradigms to study nonlinear dynamics
in real experimental systems. We report on ferromagnetic resonance experiments
in yttrium iron garnet (YIG) spheres probing regular and irregular auto-oscillations
above the first-order Suhl instability. Different invasive as well as non-invasive
techniques have been applied to suppress the observed chaotic oscillations
and to stabilize specific unstable periodic orbits:
<BR>(i) We demonstrate the suppression of chaos by fast parametric modulation
and show that the increase of modulation amplitude actually results in
an effective variation of the modulated control parameter.
<BR>(ii) The OGY method which requires precise knowledge of the unstable
periodic orbit to be stabilized makes use of the internal system dynamics
in a rather sophisticated way. In view of the fast time scale of spin systems
the application to spin-wave chaos is only possible in terms of modified
schemes based on an incomplete phase space reconstruction. We implemented
an 'occasional proportional feedback' type of control by means of a fast
electronic device.
<BR>(iii) Time-delayed feedback methods, which are of particular interest
for fast experimental systems, may be considered as an efficient compromise
combining simplicity of application with low controlling power. Although
this method has been successfully applied in many real experiments, a theoretical
understanding was supplied only very recently and allows us to optimize
the efficiency of control.
control workshop
2001-10-10