Popov M. Interaction between electric and magnetic subsystems in ferrites and composite structures on their basis

The thesis solves the important fundamental and applied problem of searching for new and in-depth analyzing of already known effects of the interaction between electric and magnetic subsystems in ferrites and composite structures on their basis at room temperature, study of the influence of electric and magnetic fields on the abovementioned structures and the justification of their possible usage in a tunable analog signal processing microwave devices. The unified conceptual approach was applied to the analysis of the mode-splitting effect in cylindrical ferrite resonators made from single-crystal cubic yttrium-iron garnet ferromagnet and single-crystal M-type hexaferrite in the millimeter wave band. It was shown that frequencies of eigenmodes with non-zero azimuthal indices can be tuned with external magnetic field by more than 1 GHz in the former case and by 10 GHz in the latter. For the first time the hysteresis behavior of magnetodynamic modes frequency with magnetic field was observed in barium hexaferrite resonator. The designs of various waveguide and microstrip line based analog signal processing microwave devices such as resonance isolators, phase shifters and band-pass filters operating in the range 20-90 GHz were suggested and characterized. They all make use of the abovementioned effect which is a direct result of the interaction between electric and magnetic subsystems in magnetic dielectrics. The resonance and relaxation properties of the coupled electromagnetic-spin oscillation in ferrite-dielectric resonators as well as the high-frequency properties of hybrid oscillations in composite resonator comprising dielectric and weak ferromagnet (iron borate) were investigated. The possibility of noticeable modification of composite resonator’s transmission characteristics, including resonance frequency, linewidth and insertion losses, under the application of external magnetic field was experimentally demonstrated. The phenomenological theory of strain induced effective magnetic anisotropy constants for the two-layer mechanically coupled ferrite-piezoelectric heterostructure was introduced and experimentally verified. It was shown that the influence of piezoelectric-generated mechanical stress on the first order uniaxial anisotropy constant in ferrite film is the dominant effect in this case. For the first time the static and dynamic properties of the domain structure in two-layer mechanically coupled ferrite-piezoelectric composite were studied by the combination of optical and radiospectroscopic techniques. It was shown that application of electric field to the piezoelectric component results in domain resonances frequency change, reorientation of the static magnetic moments inside the domain structure and control of the light scattering by the domains. These effects may become the base for the next generation magnetooptical, spintronic and straintronic devices. The experimental investigations of the two-stage filter prototype with adaptive characteristics were conducted. The resonance elements of the filter were made from the composite ferrite-piezoelectric structures. By the independent electric tuning of resonance frequency of each stage the insertion losses at center frequency were modified by 14-17 dB and 3 dB rejection bandwidth changed in 1.4-1.9 times (depending on the central frequency). For the first time the room temperature current-induced nonlinear magnetoelectric effects in the ferrites were experimentally observed and theoretically investigated. It was shown that these effects may find its practical application in current-tunable centimeter and millimeter wave signal processing devices with smaller size, weight and reduced power consumption. It was pointed out that utilization of the domain modes tuning may allow to completely get rid of bulky and heavy bias magnetic system in the millimeter wave devices design.