P. Hernandez

Simple resistance calculation in litz-wire planar windings for induction cooking appliances

We present a simple method to calculate the winding resistance of a litz-wire inductor in an induction cooking appliance, taking into account eddy-current losses, including conduction losses and proximity-effect losses. The method, which uses numerical calculation of the magnetic field, can be used to determine the optimum number of strands in the litz wire. The effects of the temperature on the winding total resistance are included in the calculation. We have built a prototype to verify the calculation method and its limitations. We consider the accuracy limits of the method.

Influence of sintering atmosphere on the magnetic after-effect in strontium ferrites

Copyright (c) 1996 Elsevier Science B.V. All rights reserved. The relaxation of the initial permeability after sample demagnetization has been measured in polycrystalline strontium ferrite samples with nominal composition SrO.6Fe 2 O 3 (M-phase), sintered under different oxygen pressures, and has been represented by isochronal curves. Very different behaviours are observed. With lower oxygen pressures the isochronal spectra are similar to the curves obtained for barium ferrites, with relaxation peaks at room temperature. In higher oxygen partial pressures, the relaxation peaks are found at lower temperatures.

Stretched-exponential approach in relaxing systems

The stretched-exponential or Kohlrausch-Williams-Watts function has been widely used in the description of a large variety of relaxation phenomena in condensed matter physics. In this work, we consider this approach as a fundamental law and extend its applicability range to thermally activated relaxation processes. A non-iterative and robust technique is developed in order to obtain the characteristic parameters of this type of phenomena. The method is based on a set of closed-form expressions for the amplitude, activation energy, pre-exponential factor and stretched-exponent that can be directly computed from isothermal curves. This strategy is applied to describe the magnetic disaccommodation spectra observed around room temperature in a magnetite sample.

Comparison between disaccommodation and ferromagnetic resonance measurements in polycrystalline yttrium–iron–garnet samples

Polycrystalline yttrium–iron–garnet (YIG) samples were sintered in air at temperatures ranging from 1350 to 1450 °C. Ferromagnetic resonance measurements have been accomplished at 11 GHz from 77 to 350 K. The different contributions to the linewidth have been analyzed. These results are compared with previous measurements of magnetic disaccommodation in the same samples. A qualitative relationship between both kind of measurements for polycrystalline YIG samples by means of an induced anisotropy formalism is provided.

Magnetic disaccommodation in single yttrium iron garnet crystal

Measurements of magnetic disaccommodation in single yttrium iron garnet (YIG) crystals are presented. Two peaks of 0.2%–0.3% are observed in the isochronal spectrum around 130 and 250 K. Comparison of our results with those on polycrystalline YIG samples and with similar data on illuminated and gamma ray irradiated single YIG crystal samples is provided.

Wideband Ferromagnetic Resonance in Nanostructured Arrays

Wideband ferromagnetic resonance at room temperature has been measured in a set of nanostructured samples: arrays of lines and antidots for Ni and permalloy-based samples. This technique allows us to determine both saturation magnetization and anisotropy constant providing valuable information about the final properties of the nanostructured material.

The magnetic disaccommodation in aluminium ferrites

Abstract The domain wall stabilization processes in aluminium substituted magnetite is investigated by means of disaccommodation techniques. The time evolution of the initial magnetic susceptibility after sample demagnetization is measured for polycrystalline specimens with nominal composition Al x Fe 3− x O 4 , 0⩽ x ⩽1, around room temperature. We show that the presence of Al 3+ ions in this structure involves the splitting of the original process III found in vacancy-doped magnetite in many similar processes, according to the different arrangements for the Al 3+ ions inside the spinel structure.

A quick and low noise sensitive technique to fit multiexponential responses

Abstract The fitting of multiexponential responses is a widely extended problem, common to many scientific disciplines. Various algorithms have been developed to solve in a more or less successful way this kind of problem. But, in all of the cases, these algorithms deal with the difficulty of the large variation of the solution when a little noise masks our data. In effect, the ill-conditioned nature of the problem restricts the accuracy of the results. This paper describes a fitting procedure, applicable in the case of multiexponential transients, for which we have checked a good capability for determining the response parameters even when we have rather low signal-to-noise ratios. This procedure combines the time domain transform technique known as the Z-transform with a technique of singularities reconstruction using the so-called Pade-approximants. We also make an approach to the effect of noise in the algorithm accuracy and how this noise can be overcome. Finally, we present a theoretical study of the behavior of the algorithm working with signals affected by a noise superposed and we check this fitting technique by analyzing the time transients, after sample demagnetization, of the magnetic reluctivity experimentally observed in a magnetite specimen near room temperature.

Photoinduced magnetic effects in bulk single-crystalline, polycrystalline, and LPE films of Yttrium Iron Garnet

The effect of light on magnetic initial permeability (the so-called photomagnetic effect) and photoinduced disaccommodation were studied in samples of yttrium iron garnet over the temperature range 77–300 K. The samples studied were bulk crystalline, produced by the floating zone method and the flux method, polycrystalline, produced by the usual sintering method, and single-crystalline films, produced by in situ liquid-phase epitaxis. One or both of the studied phenomena were observed in our experimental samples. To explain the experimental results, we suggest there is photoinduced structural distortion around oxygen vacancies due to a photoinduced change of charge imbalance.