Frederic Mazaleyrat

Stress-induced magnetic anisotropy in nanocrystalline alloys

Abstract Stress-annealing experiments were extended to both nanocrystalline alloy families, Finemet and Nanoperm (Hitperm), and, for comparison, to amorphous Fe 62 Nb 8 B 30 alloy. For both Finemet and bulk amorphous, stress-annealing results in a strong induced transversal anisotropy (flattening of hysteresis loop) but yields longitudinal induced anisotropy (square hysteresis loop) in Nanoperm and Hitperm. These results are interpreted in terms of back-stress theory.

Loss separation in soft magnetic composites

We report and discuss significant results on the magnetic losses and their frequency dependence in soft magnetic composites. Two types of bonded Fe-based materials have been characterized at different inductions from dc to 10 kHz and analyzed by extending the concept of loss separation and the related statistical theory to the case of heterogeneous materials. Starting from the experimental evidence of eddy current confinement inside the individual particles, the classical loss component is calculated for given particle size distribution. Taking then into account the contribution of the experimentally determined quasistatic (hysteresis) loss, the excess loss component is obtained and quantitatively assessed. Its behavior shows that the dynamic homogenization of the magnetization process with frequency, a landmark feature of magnetic laminations, is restrained in these materials. This results into a partial offset of the loss advantage offered by the eddy current confinement.

Magnetic properties of nanocomposites containing Fe-Ni or Fe dispersed in a Mn-Zn ferrite matrix

Summary form only given. Nanocomposites have been synthesised, by mixing in a planetary miller, of nanosized Fe/sub 25/Ni/sub 75/ or Fe and MnZn ferrite powders. Structural properties, grain size and lattice distortion were estimated by X-ray diffraction. Dispersion of the metallic particles was examined by TEM and SEM. Hysteresis loops were measured using a VSM. The powder preparation process increases the anisotropy constant of the ferrite component through the residual lattice distortion. The temperature dependence of magnetization was recorded by Faraday balance measurement, and well-defined Curie points are visible.

The Current Sensors in Power Electronics, a Review

Abstract Current sensors are widely used in all the fields of electrical engineering and power conversion. The applications are very diverse: current measurements in semiconductors, current sensing for variable speed drive, current measurement in high voltage networks. These examples show the great diversity of performances, electrical constraints and environmental constraints of these sensors. In this paper a state-of-the-art is presented about the main types of sensors, so that the user can optimise his choice with respect to the problem to solve.

Magnetic Properties of Nanostructured Spinel Ferrites

Spinel ferrite nanoparticles (NPs) have raised interest due to their potential technological applications in fields as varied as high frequency electronic device components, soil remediation, and medical diagnosis and treatments. In this paper, we present a brief review of the magnetic properties of spinel ferrite NPs (Ni-Zn, Co, and magnetite) synthesized by the polyol method, in different degrees of aggregation, from monodisperse NPs, to clusters formed by tens to hundreds of NPs. We show that the approach to saturation can be modeled with a relationship derived from the Stoner-Wohlfarth model, both for ferrimagnetic and superparamagnetic NPs. We also present a review on the magnetic properties of spinel ferrites NPs consolidated using spark plasma sintering (SPS). This technique allows the sintering of NPs to densities 90% of the theoretical value at significantly lower temperatures and shorter times than the typical sintering processes, preserving the grain size within the nanometric range. The typical sintering temperatures are in the range 350°C-750°C, for times as short as 5 min. An interesting example is magnetite, which can be obtained as NPs by polyol, followed by SPS at 750°C, temperature that usually leads to the transformation to hematite. The Verwey transition is clearly observed as a large drop in the coercive field at ~120 K.

Soft magnetic properties of nanocrystalline Fe100−xSix (15<x<34) alloys

Nanocrystalline Fe 100-x Si x (15 < x < 34) alloys have been prepared by melt spinning with high cooling rate. We have found by X-ray diffraction that the basic cubic symmetry could be extended up to 34at% Si. Around the composition of Fe 2 Si, a single-phase metastable B2 structure was found. If the quenching is not properly conducted, traces of hexagonal Fe 5 Si 3 appear, which is detrimental to the soft magnetic properties. Our M S , T C , K, D sp and p results complement the existing (up to 25at%) data and their soft magnetic properties are herein presented for the first time, The frequency dependence of the complex permeability in this high Si content region is comparable with that of NiZn ferrite.

New design of small-angle magnetization rotation device: Evaluation of saturation magnetostriction in wide thin ribbons

We present here a newly designed device allowing λS measurements on ferromagnetic ribbons (width up to 30 mm, thickness ≈20 μm). It is based on the “small-angle magnetization rotation” method. Estimation of the ac drive field and its homogeneity into the material have been looked into. Calculations by finite elements method (MAXWELL 2D) are compared to H-coil measurements. Influence of dc bias field on transverse demagnetizing field has been taken into account. The aim of this work is to analyze, by λS measurements, the evolution of composite structure (amorphous+crystalline) in accordance with annealing treatments between 450 and 600 °C of nanocrystalline Finemet Fe73.5Si15.5B7Cu1Nb3 ribbons. Results show that the value and the sign of the saturation magnetostriction λS are important because they are related to the magnetoelastic properties. Furthermore, the observed magnetoelastic behavior (via variation of magnetization energy in accordance with external applied stress) is highly dependent of the sign ...

Temperature dependence of spin resonance in cobalt substituted NiZnCu ferrites

Cobalt substitutions were investigated in Ni0.4Zn0.4Cu0.2Fe2O4 ferrites, initial complex permeability was then measured from 1 MHz to 1 GHz. It appears that cobalt substitution led to a decrease in the permeability and an increase in the μs×fr factor. As well, it gave to the permeability spectrum a sharp resonance character. We also observed a spin reorientation occurring at a temperature depending on the cobalt content. Study of the complex permeability versus temperature highlighted that the most resonant character was obtained at this temperature. This shows that cobalt contribution to second order magnetocrystalline anisotropy plays a leading role at this temperature.

Effect of temperature and time on properties of spark plasma sintered NiCuZn: Co ferrite

Spark plasma sintering is a powerful method to produce fine grain dense ferrite at low temperature. However the process, usually conducted in neutral atmosphere in a carbon die, yields carbon surface deposition and the reduction of Fe3+ into Fe2+. It is shown that subsequent annealing in air can remove carbon and under some conditions produce complete oxidation of Fe2+ ions. Regular values of the resistivity and permittivity (resp., 1 MΩm, 13 e0) are recovered for most samples annealed at temperatures not higher than 750  °C. A relatively high value of the permeability (up to 240) and a high merit factor (μs×fr>5 GHz) have been achieved.

Magnetoelectric effect in layered ferrite/PZT composites. Study of the demagnetizing effect on the magnetoelectric behavior

We report the use of high magnetomechanical coupling ferrites in magnetoelectric (ME) layered composites. Bilayer samples combining (Ni0.973 Co0.027)1−xZnxFe2O4 ferrites (x = 0–0.5) synthesized by non conventional reactive Spark Plasma Sintering and commercial lead zirconate titanate (PZT) were characterized in term of ME voltage coefficients measured at sub-resonant frequency. Strong ME effects are obtained and we show that an annealing at 1000 °C and a quenching in air improve the piezomagnetic behavior of Zn-rich compositions. A theoretical model that predicts the ME behavior was developed, focusing our work on the demagnetizing effects in the transversal mode as well as the longitudinal mode. The model shows that: (i) high ME coefficients are obtained when ferrites with high magnetomechanical coupling are used in bilayer ME composites, (ii) the ME behavior in transversal and longitudinal modes is quite similar, and differences in the shapes of the ME curves are mainly due the demagnetizing effects, (i...