Dielectric and Magnetic Measurements on Ferrite Ceramics at Millimeter Waves

Transmittance measurements on 99.9% pure yttrium iron garnets, aluminum-substituted yttrium iron garnets, gadolinium-substituted yttrium iron garnets and nickel ferrite ceramics over a broad-band millimeter wave frequency range have been performed. The measurements have been done using a free-space, quasi optical millimeter wave spectrometer in transverse magnetic field up to 8 kOe. Magneto-optical approach has been successfully employed for the separation of dielectric and magnetic effects, so that complex magnetic permeability and dielectric permittivity of ferrite materials can be determined simultaneously. Changes in magnetic permeability in transverse magnetic field due to the shift of ferromagnetic resonance to higher frequencies have been observed. Magnetic anisotropy and dissipation parameters have been calculated using Schloemann equation for partly magnetized ferrites. A high Q-factor Fabry-Perot open resonator system has also been employed for precise complex dielectric permittivity measurements of pure yttrium iron garnets and gadolinium substituted samples. A comparison of measured data and the measurement accuracy for both free-space quasi-optical technique and Fabry-Perot open resonator system have been performed.