Effective linewidth due to conductivity losses in barium ferrite at 10 GHz

The effective linewidth technique has been applied at 10 GHz and room temperature to single-crystal barium ferrite with uniaxial anisotropy. Effective linewidths were obtained from measurements of the positive field tails of the FMR (ferromagnetic resonance) absorption and dispersion curves for circular disks of barium ferrite ranging in thickness from 0.33 to 1.75 mm. The effective linewidths ranged from 125 to 2850 Oe, and vary linearly with the square of the disk thickness. This linear relation is consistent with an eddy current loss process. A fit of the data to rudimentary eddy current theory yields a resistivity of 0.8 Ω-cm. This result for the resistivity is consistent with a resistivity of 1-4 Ω-cm determined from 10-GHz dielectric measurements and 20 Ω-cm from DC resistivity measurements. The effective linewidth vs sample thickness extrapolated to zero thickness indicates an intrinsic linewidth of 60±45 Oe. The results indicate that, for barium ferrite samples thicker than about 0.3 mm, the effective linewidth losses are dominated by losses due to eddy currents in the material