Frequency dependence of microwave complex permeability under magnetic bias

Measurement of the frequency dependence of the permeability under magnetic bias is proposed as a new method for studying the microwave magnetic properties of magnetic materials. The samples under study are either rolls of thin ferromagnetic films or the composites filled with sendust particles. It is shown that the permeability measured under external magnetic bias depends on sample thickness. The correct interpretation of the measured data is possible only when sample demagnetization is accounted for. The values of the anisotropy field and the saturation magnetization of thin nitrogen doped iron films and flake-shaped sendust particles are calculated considering demagnetization of the washer-shaped sample

Frequency dependence of microwave complex permeability under magnetic bias

Measurement of the frequency dependence of the permeability under magnetic bias is proposed as a new method for studying the microwave magnetic properties of magnetic materials. The samples under study are either rolls of thin ferromagnetic films or the composites filled with sendust particles. It is shown that the permeability measured under external magnetic bias depends on sample thickness. The correct interpretation of the measured data is possible only when sample demagnetization is accounted for. The values of the anisotropy field and the saturation magnetization of thin nitrogen doped iron films and flake-shaped sendust particles are calculated considering demagnetization of the washer-shaped sample

Influence of Hydrogen Reduction Stage Conditions on the Microwave Properties of Fine Iron Powders Obtained via a Spray-Pyrolysis Technique

The relationship between the chemical purity of one-size particles and microwave properties in ferromagnetic materials is not clearly studied. Ferromagnetic nanostructured iron powders were synthesized from iron nitrate solution using ultrasonic spray-pyrolysis and then reduced in H2 flow at 350, 400, 450, and 500 °C. A rise in the concentration of solutions of a precursor from 10 to 20 wt. % led to an increase in mean particle size. The interrelationship was studied between chemical composition and the microwave dispersion of the powders obtained. An increase in the temperature of reduction changes the chemical composition and increases the amplitude of complex microwave permeability, which was studied using solid-state physics methods (XRD, STA, SEM, and VNA). It was found that annealing at 400 °C is the optimal treatment that allows the production of iron powders, consisting of about 90% of α-Fe phase, possessing a particle surface with low roughness and porosity, and demonstrating intense microwave absorption. Annealing at a higher temperature (500 °C) causes an even higher increase in permeability but leads to the destruction of nanostructured spheres into smaller particles due to grain growth. This destruction causes an abrupt increase in permittivity and therefore significantly reduces potential applications of the product. The insight into chemical–magnetic relationships of these materials enhances the data for design applications in magnetic field sensing

Past and Future of Permafrost Monitoring: Stability of Russian Energetic Infrastructure

This study is an attempt to suggest a new state system of permafrost monitoring, primarily for energetic infrastructure, based on past approaches and achievements in Russia for over a hundred years of Arctic studies. The methodology of this study is based on general theoretical methods of scientific research. Historical (retrospective analysis of the development of the monitoring system of long-term permafrost in Russia) and logical (inductive generalization) methods were applied. The structure and methods of permafrost monitoring in the Soviet Union and new technologies used nowadays to establish permafrost monitoring systems, taking into account modern Arctic energetic development, have been analyzed