Microwave characterization of complex permittivity of magnetodielectric disks with resonant methods

Accurate determination of the complex permittivity of magnetodielectric materials at microwave frequencies remains challenging, particularly for ferrimagnetic samples exhibiting strong magnetocrystalline anisotropy. In resonant methods such as the Courtney technique, separation of dielectric and magnetic contributions requires magnetic saturation of the sample; however, tensor permeability effects under bias introduce systematic errors in the extracted permittivity. In this work, the applicability of split-post dielectric resonators (SPDR) to the characterization of small thin magnetodielectric disks is investigated. Measurements were performed at 5 GHz and 10 GHz on polycrystalline yttrium iron garnet (YIG) and W-type hexaferrite disks under static magnetic bias. The results show that SPDR measurements at higher frequencies provide significantly improved sensitivity and reduced uncertainty compared to lower-frequency operation. For the investigated samples, reliable permittivity values were obtained at 10 GHz, while 5 GHz measurements were limited by small frequency shifts and their associated uncertainty.