Magnetic Properties of Nanoferrites Near Ferromagnetic Resonance in Millimeter Waves

Complex magnetic permeability and dielectric permittivity of nano-sized pure powdered and solid diluted barium and strontium ferrites have been studied in a broadband millimeter wave frequency range for the first time. Transmittance measurements have been performed using a free space quasi-optical millimeter wave spectrometer, equipped with a set of high power backward wave oscillators. Backward wave oscillators have been used as sources of tunable coherent radiation at each individual Q -, V- and W-frequency bands. Real and imaginary parts of dielectric permittivity for both types of pure and diluted nanoferrites have been calculated using analysis of recorded high precision transmittance spectra. Frequency dependences of the magnetic permeability have been calculated from Schlömann´s equation for partially magnetized ferrites. Tunable millimeter wave absorber, based on manipulating physical properties of nano-sized powdered ferrite materials and external magnetic field has been presented.