We report an improvement on a single coil technique allowing the measurement up to 6 GHz of the permeability of magnetic films, both thin and thick. The permeability is deduced from two impedance measurements, with and without a saturating magnetic field. An equivalent electrical circuit model is used to retrieve the impedance solely due to the film from the measured one. The improvement discussed in this paper is obtained by considering a single coil as a shorted microstrip and proceeding to a transmission line analysis. From it, we obtain an expression for the scaling coefficient (SC) common to thin film techniques. We prove its consistency by comparing it favorably with SCs determined from a thin film reference sample. Our technique is therefore no longer restricted by the choice of reference samples. We illustrate this by measuring magnetic films hundreds of micrometers thick and comparing the results with a coaxial line measurement.

The permeability spectra of single NiFeMo flakes have been measured within the frequency range 10 MHz–20 GHz using a high-sensitivity micro-permeameter, which we have developed. It is shown that the permeability spectrum of single flakes exhibits two resonance lines at 45 MHz and 2.8 GHz and resembles the one of flake-shaped particle composites. These two excitations exist whatever the geometrical irregularity of the flake. In addition, a comparison with the permeability spectrum of a square-shaped element suggests that the shouldering appearing in the low-frequency side of the high-frequency resonance could be attributed to domain wall resonances.

The high-frequency permeabilities of several NiZn ferrite films prepared by spray plating were investigated up to 6GHz. An adaptation of the Bouchaud–Zérah effective medium model provided an analytical expression for the microwave permeability, with a simple dependence on the magnetization distribution. An excellent agreement with the experimental results was obtained, in the demagnetized state as well as in the remnant state.

A method for determining the magneto-elastic effects in spinel ferrites at high frequencies is presented. To investigate the high-frequency properties of different ferrite materials under stress, a reflection/transmission cell had been designed. In the measurement technique described here, we use a cell which based on a modified reflection/transmission line. This setup allows measurement of permeability under stress up to 20MPa from 1MHz to 10GHz. Specific retrieval procedures have been developed to take into account the modifications in the line geometry. In this study, the permeability properties of spinel ferrites versus frequency between 1MHz and 6GHz as a function of the applied stress are showed. The two most important contributions of the permeability are the wall bulging and the gyro-magnetism which have a different behavior versus the applied stress.

The permeability of inclusions consisting of commercially available piezoelectric disks was investigated, leading to the observation of several resonances in the 100MHz–3GHz range. This could be described through a simple analytical relation, and the inclusions were deemed attractive for manufacturing metamaterials with negative permeabilities over a significant frequency range. Moreover, they can be used as reference permeability samples.

The high-frequency permeability of NiZn ferrite films prepared by roll spray ferrite plating is investigated. Significant magnetoelastic effects are observed. The permeability is nearly isotropic in film plane, and Bouchaud-Zerah effective medium model for the permeability seems to give a fair account of the permeability spectra. According to this model, the isotropic in-plane complex permeability is the square root of the hard axis gyromagnetic permeability of a thin film with uniform magnetization, which is easily expressed through Landau-Gilbert formulation. (c) 2006 Elsevier B.V. All rights reserved.

We investigate metal-dielectric inclusions that provide highly resonant permeability. These inclusions are made of high-index slabs with conductor plating on some faces. Microwave measurements are performed on several types of gratings made from these patterns. Broad band experiments are carried using a coaxial cell. Negative permeability levels lower than −20 have been observed in the GHz range, along with loss levels as low as 0.09 at μ′=−1. We show that among the different theoretical approaches that are adequate to describe these materials, the field summation approach provides a very straightforward way to derive the effective permeability. The simple analytical expression of the permeability is in excellent agreement with the experiments. These inclusions are shown to be attractive both from the technological and the intrinsic performance point of view for metamaterial manufacturing. The effects of inclusion imperfections and finite thickness are discussed.

The impedance of a planar coil suspended on a torsion beam and placed in a strong magnetic field is analyzed. It exhibits an inductive behavior with high inductance values. Numerical examples are provided for this "galavanometer type" inductor. An experimental demonstration of a magneto-mechanical system with high inductance is also shown. Potential applications and limitations are discussed

The complex permeability variation measurements at microwave frequencies of a magnetostrictive/piezoelectric bilayer under different values of a dc electric field are reported. A 25% variation of the initial permeability is achieved under a 1.5times106 V/m static electric field

On presente differentes avancees relatives a la caracterisation des proprietes electromagnetiques des materiaux en lignes de transmission ou en espace libre. La mesure des spectres de permeabilite de couches minces ferromagnetiques par perturbation de spire a ete etudiee. Des inter-comparaisons internationales associees a la conception d'echantillons de reference bases sur l'utilisation originale de meta-materiaux ont permis de valider la technique. Dans un deuxieme temps, une cellule de caracterisation des materiaux ferrite doux sous contrainte mecanique a ete developpee. Une demarche experimentale a permis de valider son fonctionnement. On a defini les limites d'exploitation de la technique et propose des ameliorations. On a enfin etudie le controle non destructif des proprietes electromagnetiques de materiaux sur la base d'une instrumentation de mesure en champ proche. On a demontre l'interet de cette approche pour identifier des dispersions locales de proprietes et les quantifier.

The studied materials are spinel ferrite Ni0,5Zn0,5Fe2O4. They were prepared through a classical ceramic way. Our approach deals with the study of the stress effect on the magnetic dynamic permeability on polycrystalline toroidal samples. Measurements are done in a coaxial wave guide between 1 MHz and 6 GHz and with an applied stress between 0 and 20 MPa. The stress is applied along the torus axis. All tested materials have a negative magnetostriction coefficient. Magneto-elastic effects on hyperfrequency permeability are very important. At low frequencies, permeability is divided by two when a 20 MPa stress is applied. In this area, permeability is due to the magnetic domain wall reversible displacement. At higher frequencies, the permeability (due to magnetization rotation) increases with stress. Between the two contributions, we can observe a crossing point. At this particular frequency, the stress has no effect on the permeability. Those results, in term of wall displacement as well as in term of gyromagnetism are well understood by a simple model based on an additional contribution of magneto-elastic energy to the anisotropic one, and the configuration of spins and domain walls in the toroidal sample.

This paper demonstrates that the monitoring of the microwave permeability of thin films is an efficient way to obtain a real-time information on the in-plane uniaxial anisotropy, both in magnitude and in direction. Theoretical guidelines required to extract relevant information on the in-plane uniaxial anisotropy are presented. This technique has evidenced a fast decrease in the anisotropy followed by a slower rotation process of the uniaxial anisotropy in a Co91Nb6Zr3 film during thermo-magnetic annealing.

Two-port coplanar ferromagnetic inductors using solid magnetic planes were fabricated on silicon. L, R, and Q measurements are presented. Cutoff frequencies exceed 10 GHz, indicating no capacitance limitation. The increase in L over the air-core value is /spl sim/15%, and the quality factor Q is of /spl sim/10 up to 1.5 GHz. The inductance scales with HA-alignment and spiral excitation ratio. Agreement with High-Frequency Structure Simulator simulations including ferromagnetic resonance led to a better understanding in terms of L and Q. Current increase in L is limited by the film thickness (0.2 /spl mu/m). Thicker films (0.5-1 /spl mu/m) would lead to larger gain over L (23% to 31%) with similar Q (/spl sim/10). The restriction in Q from the air-core inductor consists in magnetic losses but not only. Another contribution would come from anomalous ohmic losses from the spiral itself enhanced by the proximity of the magnetic planes.

This paper describes another use of the coaxial line technique for the measurement of the permittivity and permeability of magnetic and dielectric materials at elevated temperatures. The proposed modified coaxial measurement cell allows making fast and accurate broadband measurements taking advantage of a single room-temperature calibration. Measurements are performed from 50 MHz up to 20 GHz. The new coaxial cell is experimentally validated. Results for glass and ferrite samples, in the 20-300 degC temperature range, are presented

The dynamic properties of a 30-nm-thick permalloy film have been investigated through permeability measurements in the 100-MHz to 3-GHz range, in the presence of an external field applied along the easy axis. The permeability depends not only on the applied field, but also on the orientation of the field compared to the remnant magnetization of the sample. The application of an external field antiparallel to the magnetization may decrease the resonance frequency compared to the zero-field permeability. Ferromagnetic resonance equations provide a good description of the dynamic bistability at low fields, but do not account for the observed behavior in the whole bistability range. This is attributed to the occurrence of a nonuniform resonance.

Microwave permeability spectra of ferromagnetic glass-coated microwires at room temperature have already been studied. Using a new setup that we have recently developed, permeability spectra of ferromagnetic microwire at various temperatures are presented. CoFeSiB soft ferromagnetic microwires are studied from 150 K to 450 K, showing large changes in their permeabilities between 30 MHz and 3 GHz.