Broadband Microwave Characterization of Mono- and Polycrystalline Magnetic Garnet Spheres

Ferromagnetic linewidth, g-factor and magnetic anisotropy measurements of mono- and polycrystalline yttrium iron garnet (YIG) spheres performed in a subwavelength cavity are reported, covering a frequency range of up to 28 GHz. The g-factor and anisotropy field were determined by modeling the resonance frequency vs. magnetic bias dependence via an electrodynamic approach accounting for e.g. sample size effects. Two factors influencing the extrinsic (apparent) linewidth have been analyzed: the influence of changes in the Q-factor vs. intrinsic linewidth dependence and conduction losses in the cavity walls. Additionally, two-port rectangular resonant cavity linewidth measurements at a few modes have been conducted. Good agreement between the two methods has been found, except for measurements at higher frequencies where the subwavelength cavity measurements show a negative systematic error. In the polycrystalline samples, the existence of the Buffler peak was identified, which is a non-Gilbert-type increase in the ferromagnetic linewidth vs. frequency dependence.