Microwave Loss in Ultralow-Linewidth Substituted Garnets

Linewidth measurements from 77 to 300°K and room-temperature off-resonance effective linewidth data at 9 GHz show that the microwave losses in ultralow-loss Ca–V–In substituted YIG and Ca–Ge–In–YIG are completely resolvable in terms of known processes and that only a small part of the loss is due to anisotropy broadening. For the lowest linewidth of 2 Oe observed to date (Ca–Ge–In–YIG), about 0.5 Oe is due to rare-earth impurities, 0.9 Oe is from porosity broadening, and 0.2 Oe is from anisotropy. The remaining 0.4 Oe contribution is comparable to expected ``intrinsic'' single-crystal linewidths.