HIGH-FIELD EFFECTIVE LINEWIDTH AND EDDY-CURRENT LOSSES IN MODERATE CONDUCTIVITY SINGLE-CRYSTAL M-TYPE BARIUM HEXAGONAL FERRITE DISKS AT 10-60-GHZ

The losses associated with the high-field tail region of the ferromagn etic resonance (FMR) absorption curve were investigated at 10, 19, 35, and 60 GHz for 0.10-1.75-mm-thick c-plane circular disks of flux-grow n single-crystal M-type barium ferrite materials. A conventional high- field effective linewidth analysis of the data yielded an effective li newidth which increased with the square of the disk thickness and line arly with frequency, dependencies which indicate a predominant eddy cu rrent loss process. Based on these results, an eddy current loss analy sis of the tail region was done, based on the insulator FMR response a nd eddy current losses driven by the FMR response. This analysis leads to a new noninvasive technique for the determination of the microwave conductivity in moderate conductivity ferrites. One obtains the condu ctivity from an appropriate analysis of the FMR absorption tail in the same way that analysis of the magnetic loss tail yields a high-field effective linewidth. Based on this technique, the microwave conductivi ty of these flux-grown barium ferrite single-crystal materials was det ermined as a function of frequency and found to increase linearly from 0.033+/-0.004 OMEGA-1 cm-1 at 10 GHz to 0.10+/-0.02 OMEGA-1 cm-1 at 6 0 GHz. These results are consistent with a measured dc conductivity of 0.03-0.05 OMEGA-1 cm-1.