52 research outputs found
Synthesis and characterization of core-shell structure silica-coated Fe29.5Ni70.5 nanoparticles
In view of potential applications of magnetic particles in biomedicine and
electromagnetic devices, we made use of the classical Stober method
base-catalysed hydrolysis and condensation of tetraethoxysilane (TEOS) to
encapsulate FeNi nanoparticles within a silica shell. An original stirring
system under high power ultrasounds made possible to disperse the otherwise
agglomerated particles. Sonication guaranteed particles to remain dispersed
during the Stober synthesis and also improved the efficiency of the method. The
coated particles are characterized by electron microscopy (TEM) and
spectroscopy (EDX) showing a core-shell structure with a uniform layer of
silica. Silica-coating does not affect the core magnetic properties. Indeed,
all samples are ferromagnetic at 77 K and room temperature and the Curie point
remains unchanged. Only the coercive force shows an unexpected non-monotonous
dependence on silica layer thickness.Comment: Regular paper submited to international peer-reveiwed journa
Nitrogenation and sintering of (Nd-Zr)Fe10Si2 tetragonal compounds for permanent magnets applications
International audienceNd(1-x)Zr(x)Fe10Si2 alloys have been prepared in the tetragonal ThMn12-type structure by arc-melting and melt-spinning and then nitrogenated to improve their magnetic properties. For x = 0.4 and 0.6 the Curie temperature and magnetic anisotropy fields increase from 280-300 ÂşC to about 390 ÂşC and from 2.8-3 T to 4.5-5 T respectively. The saturation magnetization remains almost unchanged. The nitrogenated powders were processed by spark plasma sintering (SPS) leading to compact pellets, which retain the full nitrogen content and magnetic properties up to 600 ÂşC, but segregated Fe-Si at elevated temperatures. Nitrogenation and SPS processing are, therefore, appropriate for sintering metastable materials such as (Nd,Zr)Fe10Si2 into compact material without loosing functional properties. This opens a way towards a new family of permanent magnets, lean of critical raw materials
Enhanced magnetoelectric voltage in ferrite/PZT/ferrite composite for AC current sensor application
International audienceIn this paper, we report the fabrication of a rare-earth free current sensor based on a PZT/NiCoZn-ferrite magnetoelectric (ME) trilayer composite disk. To improve the sensitivity of the sensor, the structure uses an in-plane series connection, which increases the ME voltage by two for a fixed volume. Then, we propose a full characterization of the sensor : electrical modeling, low and high frequency limits, sensitivity, linearity, distortion and resolution. The device is also evaluated under sinus, square, and triangle waveform currents, which are excitation signals commonly used in the field of electrical engineering. The current sensor shows high current sensitivity (90 mV/A), good linearity from 0.001 A to 30 A and low added impedance (0.01 Ω) in a frequency range of 10 Hz-30 kHz for a very compact structure (4 cm 3). It also exhibits a high resolution of 1 mA (for a 1 A peak signal) and good stability
SPS co-sintered monolithic transformers for power electronics
International audiencePower integration is a key issue to reduce the volume and weight of electronic devices in power applications. But, transformers produced using classical planar assembly are limited in design. Spark Plasma Sintering (SPS) is a relatively new technology to produce multimaterial compact system with higher density and using lower sintering temperature. The purpose of this study is to manufacture of a cubic-centimeter size transformers for high frequency application using SPS. The prototype presented in this paper is composed of two spiral copper coils separated by an insulated layer and encapsulated in ferrite powder. The assembly is then co-sintered by SPS. The magnetic material used for the transformers is a nickel-zinc based ferrite, with copper substitution to allow sintering at low temperatures. The low conductivity of this mixed-ferrite ensures operation in the frequency range of 1 to 20 MHz of our final system. Computed tomography scanning has been used to optimize the design of the co-sintered structures. Effects of the composition of the ferrite and the sintering temperature on the transformation ratio are discussed. It is shown that a ferrite with very low conductivity is required to ensure galvanic insulation, as there is a direct contact between the copper spirals and the magnetic parts
Cation distribution effect on static and dynamic magnetic properties of Co 1-x Zn x Fe 2 O 4 ferrite powders
International audienc
Loss decomposition in plastically deformed and partially annealed steel sheets
There is increasing interest in the optimization of non-oriented electrical steels for applications under excitation frequencies above 400 Hz. We discuss in this paper the possibility of a new manufacturing procedure, where skin-pass and subsequent heat treatment for recovery are applied as the two last stages of sheet processing. Samples from a commercial non-oriented 3 wt% silicon steel were submitted to 2.5% thickness reduction and were heat treated at temperatures ranging between 600 and 850 °C for 2 h. It is shown that, although the hysteresis loss increases with plastic deformation, the excess loss decreases in such a way that under increasing magnetizing frequencies the total energy loss of the deformed and recovered sample becomes lower than in the starting material. The higher the annealing temperature the lower the frequency at which crossover of the loss curves is observed, as long as full recrystallization does not occur. It is assumed that with the dislocation structures left in the deformed and partially recovered samples one achieves a condition of increased fragmentation of the magnetization process, that is, of increased number of concurring correlation regions (Magnetic Objects). The corresponding decrease of the excess loss component can eventually overcompensate the deterioration of the quasi-static magnetic properties, leading to lower total losses
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