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the best ways in order to reduce fuel consumption for vehicles. It consists of associating an electric motor next to the classical thermal machine. In this embedded system, the efficiency and the torque per unit mass are very important. So it seems to be a good idea to use a permanent magnet synchronous machine, which is recognized for satisfying these two objectives. Since the allocated volume is rather flat, axial flux topologies are interesting. This paper’s goal is to propose an optimal first design method for such structures, given the allocated volume and the machine requirements. La traction hybride semble actuellement un des moyens les plus prometteurs pour réduire la consommation de carburant des véhicules. Ce procédé consiste à associer un moteur électrique au moteur thermique traditionnel. Pour une telle application embarquée, le rendement, ainsi que le couple massique, sont des critères de conception de première importance. Dans ce contexte, le recours à une machine synchrone à aimants permanents, reconnue pour satisfaire ces deux critères, semble être approprié. Vu que le volume alloué à la machine électrique est de forme discoïde, les topologies à flux axial semblent les plus intéressantes. L’objectif de cet article est de proposer une méthodologie de pré-dimensionnement de tels actionneurs, en ayant fixé au préalable le volume maximal permis ainsi que le cahier des charges de la machine.

Magnetic viscosity measurements performed on nanocrystalline SmFeCo spring magnets with different Fe content are analyzed by the Preisach hysteresis model. The model gives a unified description of hysteresis and relaxation properties. Comparison between calculated and measured viscosity permits one to estimate the aftereffect activation volume r. Calculated [v.sup.1/3] values are approximately equal to the average grain size of the hard phase. Index Terms - Aftereffect, hysteresis models, nanocrystalline hard materials, thermal activation.

We have investigated the magnetoelectric (ME) effect in layered composite rings subjected to circumferential AC magnetic fields and DC magnetic fields in radial, axial, or circumferential directions. Bilayer samples were obtained combining different grades of commercial Mn-Zn ferrites or Ni-Zn ferrites with commercial lead zirconate titanate (PZT). Mn-Zn ferrites with low magnetostriction saturation (λs < 10-6) and low magneto-crystalline anisotropy constants show high ME capabilities when associated with PZT in ring structures. In certain conditions, these ME effects are higher than those obtained with Terfenol-D/PZT composites in the same layered ring structure. Magnetostrictive and mechanical characterizations have given results that explain these high ME performances. Nevertheless, Mn-Zn ferrite/PZT composites exhibit voltages responses with low linearity especially at high signal level. Based on the particular structure of the ME device, a method to decrease the nonlinear harmonic distortion of the ME voltages is proposed. Harmonic distortion analysis of ME voltages measured in different configurations allows us to explain the phenomenon. [ABSTRACT FROM AUTHOR]

Structural and magnetic characterization of Mnx−yAl100−x−yC2y (x = {50, 55}; y = {0, 1}) melt­spun ribbons is reported. To obtain the metastable ferromagnetic τ­phase, rapidly solidified alloys were annealed either in a vacuum furnace at 823 K or directly in the vibrating sample magnetometer under applied magnetic field. Optimal magnetic properties were demonstrated by Mn54Al44C2 samples proved to be single­phase with a coercivity of 0.19 T measured in both cases. For this composition the structural ε→τ phase transformation has been magnetically detected at 786 K, Curie temperature of τ­phase (Tc = 592 K, Tp = 610 K) has been determined using mean field approximations in ferromagnetic and paramagnetic regions. Rietveld refinement of X­ray diffraction spectra was employed to analyse the phase constitution of annealed alloys, lattice parameters as a function of chemical composition and mean grain size for the phases involved.

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, (iii) in the transversal mode, the magnetic field penetration depends on the ferrite layer thickness and the ME coefficient is affected accordingly. The two later points are confirmed by measurements on ME samples and calculations. Performances of the ME composites made with high magnetomechanical coupling ferrites are compared to those obtained using Terfenol-D materials in the same conditions of size, shape, and volume ratio. It appears that a ferrite with an optimized composition has performances comparable to those obtained with Terfenol-D material. Nevertheless, the fabrication processes of ferrites are quite simpler. Finally, a ferrite/PZT based ME composite was used as a current sensor. [ABSTRACT FROM AUTHOR]

Research into the interaction between activation volumes and microstructure in nanocrystalline Fe73.5Cu1Nb3Si13.5B9 (Fimemet) alloys is presented. It is suggested that there is a broad distribution of activation volumes controlled by structural disorder.

We present experiments on nanocrystalline materials where thermal activation gives rise to dynamic effects on hysteresis curves. A scheme of interpretation is presented and the typical activation volume is found to be about 100 nm. Index Terms - Thermal activation. Dynamic hysteresis loops. Nanocrystalline soft materials. Magnetic hardening.

Magnetic viscosity measurements on NdFeB spring-magnets are interpreted by means of a thermodynamic generalization of the Preisach hysteresis model. The model correctly predicts the observed decay of magnetization and clarifies the connection between anomalous, non-monotone after-effect and applied field history. Comparison between theory and experiments permits one to estimate the after-effect activation volume, [d.sup.3] [approximately equal to] [(12 nm).sup.3], and the attempt frequency 1/[[Tau].sub.r] [approximately] [10.sup.10] [s.sup.-1].

A thermodynamic model of hysteresis is presented based on an internal variable reinterpretation of the Preisach model. The model is applied to the prediction of nonmonotonic heat exchange along the hysteresis loop measured for ferromagnets.

The isotropic properties of Soft Magnetic Composites (SMC) favor the design of new machine topologies and their granular structure can induce a potential decrease of the dynamic loss component. This paper is devoted to the characterization of the broadband magnetic losses of different SMC types under alternating and circular induction. The investigated materials differ by their grain size, heat treatment, compaction rate, and binder type. It is shown that, up to peak polarization Jp=1.25 T, the ratios between the rotational and the alternating loss components (classical, hysteresis, and excess) are quite independent of the material structural details, quite analogous to the known behavior of nonoriented steel laminations. On the contrary, at higher inductions, it is observed that the Jp value at which the rotational hysteresis loss attains its maximum, related to the progressive disappearance of the domain walls under increasing rotational fields, decreases with the material susceptibility. [ABSTRACT FROM AUTHOR]

Magnetic properties of nanocrystalline Finemet ribbons with composition [Fe.sub.73.5] [Cu.sub.1] [Nb.sub.3] [Si.sub.13.5] [B.sub.9] are studied. Six different samples annealed for 1 hour at different temperatures are studied. Measurement of hysteresis loops and of relaxation, performed at temperature above the Curie point of the amorphous phase, are presented and discussed. Index Terms--Nanocrystalline soft materials, thermal relaxation, hysteresis, superparamagnetism.

A vector model of magnetic hysteresis in biaxial anisotropy structures is presented, in which magnetoelastic effects are explicitly taken into account. The magnetization vector of individual grains is forced to lie along one of the easy axis, and jumps from one easy direction to another controlled by the sum of the external field and magnetoelastic energy.