Complex Magnetic Permeability and Dielectric Permittivity of Ferrites in Millimeter Waves

We report a first-time study of complex magnetic permeability and dielectric permittivity of 99% pure powdered barium cobalt ferrite (Ba₂Co₂Fe₁₂O₂₂) and pure solid barium hexaferrite ceramics (BaFe₁₂O₁₉) in a broadband millimeter-wave frequency range. We performed transmittance measurements using a free-space quasi-optical millimeter-wave spectrometer, equipped with a set of high-power backward-wave oscillators as sources of tunable coherent radiation at each Q-, V-, and W-frequency band. We calculated frequency dependences of complex permittivity for both types of ferrites using analysis of recorded high-precision transmittance spectra and obtained frequency dependences of the magnetic permeability from Schlomann´s equation for partially magnetized ferrites.