Мессбауэровские исследования и микроволновые свойства гексаферритов бария с замещением ионами Al-=SUP=-3+-=/SUP=- и In-=SUP=-3+-=/SUP=-

The correlation of the chemical composition, the structure, and the microwave characteristic of solid solutions of the BaFe_12 – x D_ x O_19 (0.1 ≤ x ≤ 1.2) barium hexaferrite substituted with diamagnetic Al^3+ and In^3+ ions has been studied. The precise data on the crystal structure have been obtained by powder neutron diffraction using a high-resolution Fourier diffractometer (Dubna, JINR). The data on the distribution of the diamagnetic substituting ions in the hexaferrite structure have been obtained by Mössbauer spectroscopy. The microwave properties (the transmittance and the reflectance) have been studied in the frequency range 20–65 GHz and in external magnetic fields to 8 kOe. It is found that the transmission spectra are characterized by a peak that corresponds to the resonant frequency of the electromagnetic energy absorption, which is due to the ferromagnetic resonance phenomenon. The correlation of the chemical composition, the features of the ion distribution in the structure, and the electromagnetic properties has been revealed. It is shown that external magnetic fields shift the absorption peak of electromagnetic radiation to higher frequencies due to an increase in the magnetocrystal anisotropy. The results enable the conclusion that the features of the intrasublattice interactions and the electromagnetic properties should be explained using the phenomenological Goodenough–Kanamori model.

THE MICROWAVE PROPERTIES OF THE DOUBLE-SIDED THIN FILM MgB2 RESONATOR

Double-sided magnesium diboride ( MgB 2) thin films have been grown on double-sided polished sapphire substrates by the technique of hybrid physical chemical vapor deposition (HPCVD). The zero resistance temperature ( Tc ) of the films is higher than 37 K. The microwave characteristic of the double-sided MgB 2 thin films at 8.7GHz is studied systematically by the microstrip resonator technique. Surface resistance of the thin films is extracted by analyzing the resonance curves at different temperatures, and it is 1.2 mΩ at 11K.

Microwave Dielectric Properties of Mn-Doped Ba4.5Sm9Ti18O54 Ceramics

The different amounts of manganese dioxide were doped to Ba4.5Sm9Ti18O54 (BST)ceramics. It was found that the doping sequence of Mn had serious influences on the microwave dielectric properties of the BST ceramics. When manganese dioxide was added before the mixtures were calcined, the dielectric properties of ceramics were poor and decreased with the increase of the Mn content. When the Mn content was between 2.0wt% and 3.0wt%, the BST ceramics had no microwave characteristic. But adding manganese dioxide in a range of 0.0 to 1.0wt% after the mixtures were calcined enhanced the microwave dielectric properties of the BST ceramics. When the Mn content changed from 0 to 1.0wt%, the microwave properties of the BST ceramics increased, but the microwave properties decreased while the Mn content was over 1.0wt%. The ceramics with 3.0wt% Mn content had also no microwave characteristic. The optimum microwave dielectric properties were as follows: εr=76, Q·f=7280,τf=-3.6ppm/k.