Influence of Fe2+ on microwave behaviour of M(Co, Ti)l,2 type hexaferrite

This work deals with M-type Co,Ti substituted barium hexaferrite, Ba(CoTi)xFe12-2xO19 studied near the uniaxial-planar transition ( x ≥ 1.2). A single crystal state like was obtained by using textured ceramic. Our aim is to observe the effect of the divalent iron ions on the permeability curves. We have correlated the presence of Fe2+ ions with the variation of the value of the permittivity ε at 0.1 GHz. The concentration of Fe2+ ions has been varied by annealing the sintered materials under either reducing (N2) or oxidizing (O2) atmosphere. We have tried to interprete the important variations of the permeability in terms of domain wall and gyromagnetic contributions

Study of the Gyromagnetic Resonance Damping in Relaxing Rare Earth Substituted YGd2Fe5O12 Garnets

The influence of magnetic state (saturated or unsaturated states) on the gyromagnetic resonance damping in relaxing rare earth substituted Y1-xDyxGd2Fe5O12 garnets (with x=0;0.15;0.3;0.6) has been studied. The damping parameter α, as defined by Landau-Lifshitz equation, has been determined either by FMR at 10GHz (saturated state) or by measurement of the frequency dependence of the complex initial permeability in the 0.1GHz-10GHz band (unsaturated state). On the one hand, the damping parameter αsat has been calculated by fitting the FMR spectra of single crystals with the theoretical lorentzian shape. On the other hand, the damping parameter αunsat of polycrystals has been calculated using models which take into account the interaction between magnetic domains. In the fully magnetized state the introduction of relaxing rare earth (Dy) is found to increase significantly αsat values (from 0.02 to 0.3 when x varies from 0 to 0.6). On the contrary, the introduction of Dy hardly increases αunsat values. It appears that the difference between αsat and αunsat values stems not only from the interaction between magnetic domains but also from the modification of the damping in each magnetic domain owing to the presence of magnetic domain walls

Microwave behaviour in Z-type polycristalline hexaferrites

The hexaferrites present today a great interest in the field of electromagnetic waves absorbents. We have studied Ba3Co2Fe24O41 Z-type hexaferrites. The origin of magnetic permeability in such polycrystalline materials is not so far perfectly known, especially in terms of relations between properties and microstructure. The purpose of this paper is to illustrate some of the issues involved in designing ferrite materials. On the one hand we have dealt with the relation between the elaboration conditions of the materials and their microstructure. On the other hand the influence of the microstructure on microwave behaviour has been studied. Investigated materials were in an intermediate state between the poly and single crystalline one

Gyromagnetic resonance damping in garnets : comparison between saturated and unsaturated states

Communication to : 7th joint MMM - INTERMAG, San francisco (US), January 6-9, 1998SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1998 n.28 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Discrimination of Nuclear Explosions against Civilian Sources Based on Atmospheric Xenon Isotopic Activity Ratios

A global monitoring system for atmospheric xenon radioactivity is being established as part of the International Monitoring System that will verify compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) once the treaty has entered into force. This paper studies isotopic activity ratios to support the interpretation of observed atmospheric concentrations of (135)Xe, (133m)Xe, (133)Xe and (131m)Xe. The goal is to distinguish nuclear explosion sources from civilian releases. Simulations of nuclear explosions and reactors, empirical data for both test and reactor releases as well as observations by measurement stations of the International Noble Gas Experiment (INGE) are used to provide a proof of concept for the isotopic ratio based method for source discrimination

Environmental Radioxenon Levels in Europe: a Comprehensive Overview

Activity concentration data from ambient radioxenon measurements in ground level air, which were carried out in Europe in the framework of the International Noble Gas Experiment (INGE) in support of the development and build-up of a radioxenon monitoring network for the Comprehensive Nuclear-Test-Ban Treaty verification regime are presented and discussed. Six measurement stations provided data from 5 years of measurements performed between 2003 and 2008: Longyearbyen (Spitsbergen, Norway), Stockholm (Sweden), Dubna (Russian Federation), Schauinsland Mountain (Germany), BruySres-le-ChA cent tel and Marseille (both France). The noble gas systems used within the INGE are designed to continuously measure low concentrations of the four radioxenon isotopes which are most relevant for detection of nuclear explosions: (131m)Xe, (133m)Xe, (133)Xe and (135)Xe with a time resolution less than or equal to 24 h and a minimum detectable concentration of (133)Xe less than 1 mBq/m(3). This European cluster of six stations is particularly interesting because it is highly influenced by a high density of nuclear power reactors and some radiopharmaceutical production facilities. The activity concentrations at the European INGE stations are studied to characterise the influence of civilian releases, to be able to distinguish them from possible nuclear explosions. It was found that the mean activity concentration of the most frequently detected isotope, (133)Xe, was 5-20 mBq/m(3) within Central Europe where most nuclear installations are situated (BruySres-le-ChA cent tel and Schauinsland), 1.4-2.4 mBq/m(3) just outside that region (Stockholm, Dubna and Marseille) and 0.2 mBq/m(3) in the remote polar station of Spitsbergen. No seasonal trends could be observed from the data. Two interesting events have been examined and their source regions have been identified using atmospheric backtracking methods that deploy Lagrangian particle dispersion modelling and inversion techniques. The results are consistent with known releases of a radiopharmaceutical facility