Скачкообразные квантовые фазовые переходы в вихревой системе и динамическая комплексная магнитная проницаемость двойниковых YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-x-=/SUB=- высокотемпературных сверхпроводников

A nonlocal high-frequency method for measuring the dynamic complex magnetic permeability with enhanced spatial resolution is developed to simultaneously determine the bulk and local character of stepwise penetration of a magnetic flux through twin boundaries (TBs) into a YBa2Cu3O7-x HTSC sample during its stepwise decomposition into twins. By the values of fields corresponding to the regions of steps, the thermodynamic first critical magnetic fields are determined: the penetration of a flux into a sample – a Josephson medium; the development of a critical state in the Josephson medium; the penetration of a flux into twins; and the values of the critical fields of phase transitions in the vortex system of the HTSC sample, such as the melting fields of a vortex crystal, the formation of a superconducting glass state in the sample, and the transition to the vortex glass and Bragg glass states.

Магнитные и радиопоглощающие свойства поликристаллического феррита-шпинели Li-=SUB=-0.33-=/SUB=-Fe-=SUB=-2.29-=/SUB=-Zn-=SUB=-0.21-=/SUB=-Mn-=SUB=-0.17-=/SUB=-0-=SUB=-4-=/SUB=-

Polycrystalline spinel ferrites of the composition Li0.33Fe2.29Zn0.21Mn0.17O4 were synthesized by using the ceramic technology method at sintering temperatures of 950 ° C, 1000 ° C, 1050 ° C, and 1100 ° C. Magnetic hysteresis loops and magnetic permeability of the experimental samples were studied in the range of magnetic fields of -400–400 A/m. In the frequency range of 0.01–7.0 GHz, the behavior of the complex dielectric and complex magnetic permeability, as well as the reflection coefficient on a metal plate, are investigated. It was found that the optimal sintering temperature range for synthesized ferrites is from 1050 ° C to 1100 ° C. It is shown that the spinel ferrite Li0.33Fe2.29Zn0.21Mn0.17O4 intensely absorbs electromagnetic radiation in the frequency range from 0.05 to 7.0 GHz. Possibilities of practical application of the obtained results are discussed.

Electromagnetic characterization of Ni0.5Zn0.3Co0.2Fe2O4 bulk ceramics in the 1MHz-12GHz frequency range

In this paper, NiZnCo ferrite was produced by solid state synthesis, calcination at 1000?C and sintering at 1250?C in air atmosphere. The microstructure and phases of the sintered sample were analysed by scanning electron microscopy and X-ray diffraction, respectively. The magnetic properties of the ferrite were evaluated by magnetization and magnetostriction measurements. The complex magnetic permeability and complex permittivity were also measured between 1MHz-12GHz and the reflection loss (RL) was calculated in the 100MHz-12GHz frequency range. The results show that the ferrite sample presents magnetostrictive behaviour and a saturation magnetization of 71 Am2/kg. Complex permittivity measurements indicate that the material has dielectric behaviour in the whole frequency range studied, with "? varying between 7-40, and magnetic behaviour in frequencies between 1MHz-5GHz. The minimum RL was found at frequencies between 2.4-3.3GHz and the calculated RL value for a thickness of 3mm was lower than ?10 dB in frequencies between 2.3-7.3GHz. These results indicate potential application as microwave absorber in the S band.

Microwave Characterization of Metal-Decorated Carbon Nanopowders Using a Single Transmission Line

This paper presents a novel approach for the characterization of microwave properties of carbon-based nanopowders, decorated or not with magnetic nanoparticles. Their microwave parameters, dielectric constant, electrical conductivity, and complex magnetic permeability are extracted from measurements performed using a single transmission line acting as a test cell. Two geometries of transmission line were tested, and successful results were obtained with each one of them. The measurement results are assessed by a phenomenological model enabling to fit the measurement of the dielectric constant and conductivity, providing an insight on the compacity quality of the powder sample. Also, the extraction of the permeability is validated by the detection of a ferromagnetic resonance showing a linear dependence on external DC magnetic field.