Nikytenko A. Spectral characteristics of elementary excitations in M-type hexaferrites in mm-wave range.

This work is dedicated to the experimental study of frequency-field dependences of magnetostatic (MSO) and hybrid electromagnetic-spin oscillations (EMSO) in a single-crystal barium hexaferrite BaFe12O19 with controlled domain structure (DS), as well as composite structures on its basis; and to the development of the cylindrical domain structure (CDS) regularization method. The method of CDS regularization in a single-crystal barium hexaferrite has been proposed. The influence of the CDS regularization on the characteristics of the MSO spectrum in the barium hexaferrite is analyzed and it is established that in the fields of regularization within the limits Hreg = 3 ÷ 3.6 kOe it is possible to increase the intensity of the high-frequency domain MSO mode by at least ΔS11 ≈ 4.5 dB. The phenomenon of hybridization of the lowest frequency experimental MSO mode in a BaFe12O19 plate with electromagnetic mode of a quartz dielectric resonator (DR) in the form of a disk was recorded, for three types of DS — stripe DS (SDS), CDS and CDS with inclusions of SDS with the application of an external magnetic field H0 perpendicular to the axis of easy magnetization (Н0⊥EAM). The simultaneous hybridization of both low-frequency MSO modes with the electromagnetic mode of DR in the studied composite ferrite-dielectric structure with pre-created CDS and CDS with SDS inclusions was revealed, as a result, three hybrid quasi-electromagnetic modes were obtained simultaneously for the first time even in the absence of a magnetization field. Tunable ferrite-dielectric resonator is proposed. The magnetic tuning of the four hybrid electromagnetic-spin oscillations modes frequencies can be more than 1 GHz in such a resonator in the case of pre-formed CDS with SDS inclusions at a change of the field H0 in the range of 0 ÷ 4.79 kOe, which is confirmed by the patent for the useful model. The generalization and analysis of the properties of high-frequency magnetic hysteresis inherent to single-crystal M-type hexaferrites was carried out. It has been shown experimentally that during the demagnetization of barium hexaferrite after formation of inversely magnetized domain germs, the instantaneous displacement of the domain boundaries does not occur until further reduction of the external magnetic field H0 below a certain value. In a series of experiments, it was found a shift of the MSO frequency-field dependence into the high-frequency region because of the decrease of the Hsat value for thick specimens (tf > 100 μm).