Spin-wave and effective linewidths of lithium ferrites

The spin-wave linewidth ΔHK of microwave materials may be increased by substituting relaxing ions such as cobalt. However this procedure has the disadvantage that the effective linewidth ΔHeff is also increased. Alternative ways of increasing the spin-wave linewidth of lithium ferrites with saturation magnetizations between 2500 and 5000 G have been investigated with the aim of obtaining high power handling materials with reduced off-resonance magnetic losses. This has been achieved either by hot pressing the material to reduce the grain size (if no titanium is present) or by substituting zinc as well as cobalt. Materials with ΔHK≥20 Oe have been obtained in this way with reduced cobalt content and lower effective linewidths. A broadband method of determining the effective linewidth between 4 and 11 GHz has been developed using the TM010 and TM011 resonant modes of metallized cylinders of the ferrite. These measurements show that the effective linewidths of the materials studied vary linearly with the frequency.