Quadratic frequency dependence of spinwave instability thresholds from fast-relaxing ions

The effects of fast-relaxing ions on the microwave frequency dependence of the spinwave instability threshold h/sub c/ and the imaginary permeability mu " of ferrites is examined. The role of fast relaxing ions in raising spinwave instability thresholds and average power absorption in microwave ferrites is analyzed by introducing rare-earth single-ion relaxation concepts into conventional FMR (ferrimagnetic resonance) theory. The agreement between theory and earlier experimental results confirms that the increase with frequency is quadratic for h/sub c/ and inverse linear for mu ".>