L. V. Chevnyuk’s research while affiliated with Taras Shevchenko National University of Kyiv and other places

Bandpass transmission line on the basis of uniaxial single-crystal hexaferrites in multidomain area has been proposed in this paper. This line can be used for experimental investigation of excitation and propagation of magnetostatic waves within millimeter wave range in uniaxial single-crystal hexaferrites as well as for designing of bandpass filters and delay lines. Based on it model of tunable bandpass filter with platelet of single-crystal barium hexaferrite in multidomain area with domain structure of some definite type has been designed for the first time. The work presents results of experimental investigations into conditions of excitation and propagation of magnetostatic waves in single-crystal platelet of barium hexaferrite which is the main functional element of the proposed bandpass filter. It has been found out that power attenuation of magnetostatic waves during their propagation is the key factor of signal transmission in the investigated model. It is shown that there is a correlation between intensity, bandwidth of magnetostatic resonances and efficiency of magnetostatic waves transmission in the multidomain area.

The effect of magnetic hysteresis in M-type hexaferrite single crystals has been studied experimentally. Earlier experimental data for the special aspects of the magnetic spectrum hysteresis, the parameters of which differ considerably from those of well-studied classical hysteresis, have been discussed. It has been shown that, after the nucleation of oppositely magnetized domains, the domain walls do not shift until the external magnetic field acquires a certain value.

Hybrid electromagnetic-spin oscillations in ferrite-dielectric structure consisting of a single-crystal BaFe12O19 platelet and a dielectric disk-shaped resonator in multidomain state of ferrite have been investigated by experiment. Experiments were conducted with different types of domain structures, and the frequency-field spectra were measured at tangent magnetization. It was shown that the effective hybridization of electromagnetic and magnetostatic modes in such resonator could implement such excitation regime, where one electromagnetic mode of dielectric resonator is split into three hybrid quasi-electromagnetic oscillations even in the absence of external magnetizing fields.

Prototype of bandpass filter based on single-crystal platelet of hexaferrite in multidomain area with stripe domain structure in the initial state was proposed for the first time. Designed and experimentally studied filter has 3dB-bandwidth of 80 MHz within frequencies about 47 GHz in absence of external biasing magnetic field. The filter has insertion loss of 52 dB which can be significantly decreased with optimization of conditions for excitation and receiving of magnetostatic oscillations.

The spectra of hybrid EMSOs in the composite ferrite-dielectric structure based on single crystal BaFe12O19 with the MDS in initial state were experimentally investigated. As it can be seen from Fig. 2 the fact of simultaneous hybridization of both MSOs modes ω1 and ω2 with DR electromagnetic mode one has been revealed. It should be emphasized that as the result of ω1 and ω2 interaction with DR electromagnetic mode the three quasi-electromagnetic modes are observed for the first time even at low external in-plane static biasing magnetic fields.

Self-biased millimeter wave (mm-wave) notch filter consists of a resonator based on single crystal barium hexaferrite (BaFe12O19), which is operated in the multidomain region has been realized and investigated. The filter is designed using the length of dielectric waveguide. Depending on the type of preliminary created regular domain structure in hexaferrite the filter resonance frequency fr can vary in the range of 47-51 GHz, with a maximum rejection at the frequency fr of about 22-24 dB and 3dB-bandwidth of about Δf = 50 MHz. Also, it is shown that the resonance frequency fr of such a filter is tunable in the range of 45-57 GHz by applying a low external DC magnetic biasing fields H0<4πMs to the hexaferrite resonator.

Experimental investigations of FMR frequency-field dependencies of a single crystal barium hexaferrite (BaM) platelet in the case of in-plane bias field H0, i.e. H0 is oriented perpendicular to the easy axis (EA) both in the multi-domain and saturated state, are carried out. In the domain area the case of cylindrical magnetic domains (CMD) structure is studied. The comparison of experimental results and theoretical calculations were carried out.

High-frequency characteristics of mm-range resonators produced from bulk single-crystal material and epitaxial films of barium hexaferrite doped with aluminum (BaFe11.1Al0.9O19 ) have been investigated in this study. It was shown that the composition of magnetostatic (MS) oscillations modes of the single-crystal resonator of BaFe11.1Al0.9O19 in a saturated state and in multidomain area (a case of cylindrical magnetic domain (CMD)) notably differs from resonators of BaFe12O19. Especially this difference is evident in a saturated state, when for the resonator of substituted hexaferrite a more intensive fundamental mode ω0 as compared with higher MS oscillation modes has been experimentally observed. The mode (1,1,0) was theoretically calculated in the magnetostatic approximation and was not observed experimentally. As a result of substitution with aluminum, the anisotropy field На in single-crystal resonators, with the same parameter of substitution, is higher than in epitaxial films.

In the paper for the first time it is shown that a single crystal barium hexaferrite with an easy axis (c-axis) lying in the sample plane can be used as a self-biased mm-wave ferrite resonator with two intensive resonances. It is experimentally established that the domain structure (DS) of this sample in a completely demagnetized state is the closest to the structure of parallel strip domains structure (PSDS).

In this paper it is considered an idea of application specificities of hysteresis loop of frequency-field dependence of ferromagnetic resonance of good monocrystal hexaferrite materials for creation of pulse-switchable resonator for millimeter wavelength range. The essence of principle of this device lies in possibility of quick change of the hexaferrite resonator frequency from higher frequencies to lower and inversly, “switching” the hexaferrite onto definite magnetic states. The idea was realized in a prototype device with resonator from barium hexaferrite BaFe12O19. It is stated experimentally that maximal tuning range can achieve 3.5 GHz, and the time for tuning is about 200 µs in case of magnetic field pulse is about 1.5 kOe.