It was anticipated that ferrimagnetic hexagonal compounds such as BaFe12019, SrFei 2019 andSrAl2Fe 10019 have magnetic resonance absorptions at frequencies beyond 30 GHz. We have mixedpowder specimens of such materials and deposited in paint form on one surface of a optically polishedfused silica glass substrate. The ferromagnetic resonance was then studied as functions of appliedexternal magnetic field intensity, specimen thickness and continuous frequency at millimeter wavelengthregion. A new dispersive Fourier transform spectrometer was designed and constructed to measure the realand imaginary parts of complex magnetic permeability and real and imaginary parts of complex dielectricpermittivity as a continuous function of frequency from about 10 mm wavelength to up to one millimeterwavelength range.
Mohammed N. Afsar,
"Millimeter wave radar absorbing materials", Proc. SPIE 2104, 18th International Conference on Infrared and Millimeter Waves, 21042F (30 August 1993); doi: 10.1117/12.2298519; https://doi.org/10.1117/12.2298519