Eddy Current Contribution Research Articles

Dependence of the ferrimagnetic resonance linewidth on sintering conditions in manganese ferrite

Ferrimagnetic resonance linewidth of manganese ferrites, Mn1.0Fe2.0O4 has been measured at 8.9 GHz from 77 to 320 K. Single crystal was prepared by floating zone technique and their composition confirmed by inductively coupled plasma spectrometry. Polycrystalline samples were sintered under different conditions of temperature, time, and atmosphere. Eddy current and valence exchange contributions according to Sparks’ theory and a new procedure for evaluating superficial and porosity mechanisms are taken into account to analyze the ferrimagnetic resonance linewidth. Different contributions are present depending on sintering conditions: valence exchange mechanism appears only in samples sintered under low temperatures and high pressures; conductivity decreases for samples sintered at high pressures; porosity is highly raised up when sintering time decreases. Resonance fields, obtained from experimental data, are used to calculate anisotropy fields for polycrystalline samples.

Frequency dependence of the ferromagnetic resonance and effective linewidth in single crystal manganese doped barium ferrite (abstract)

The frequency dependence of the ferromagnetic resonance (FMR) linewidth and effective linewidth has been measured in Mn doped single crystal barium hexaferrite (BaFe12−xMnxO19) with x=0.1. Mn doped samples were used to minimize conductivity losses. Measurements were made on c-plane thin disks magnetized to saturation along the disk axis and c direction. A shorted waveguide technique was used to measure the FMR profiles in the range of 55–90 GHz. The FMR field position increased linearly at 0.35 kOe/GHz, with a zero field extrapolation of 34.7 GHz as expected for uniform mode FMR in barium ferrite. The linewidth ΔH increased linearly with frequency at 0.29 Oe/GHz with a zero frequency extrapolation of 18 Oe. A high-Q cavity method was used to measure the high field effective linewidth, ΔHeffFF at 10, 20, 35, and 60 GHz. The effective linewidth increased linearly with frequency at 0.4 Oe/GHz, with a zero frequency extrapolation of 4 Oe. There were no dependencies of ΔH or ΔHeffFF on sample thickness. These results indicate that (1) eddy current contributions to ΔH and ΔHeffFF in these Mn doped barium ferrite materials are absent, (2) ΔHeffFF is significantly lower than ΔH and appears to be a good measure of the intrinsic losses, and (3) both linewidths increase linearly with frequency at about the same rate. These intrinsic linewidths in barium ferrite are still significantly greater than linewidths in yttrium iron garnet. Research sponsored in part by the United States Office of Naval Research, Contract No. N00014-90-J-4078. The single crystal samples were kindly provided by M. A. Wittenauer, Purdue University.

Analysis for Domain Dynamics in Amorphous Magnetostrictive Wires of the Composition (Fe77.5Si7.5B15)

Domain wall processes (domain wall configuration, propagatation and collapse) in magnetostrictive amorphous wires of the composition (Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">77.5</inf> Si <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7.5</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</inf> ) were investigated. The wires were held under tensile stress (up to 1700 MPa in the case of asquenched). The domain wall length and normal mobility (or damping) as functions of applied stress were found experimentally and theoretically from an ellipsoidal domain model. This alloys the losses to be separated into eddy current and spin relaxation contributions. It was demonstrated that the process of domain collapse affected by internal magnetic field generated a very sharp voltage pulse. The change in the voltage pulse shape with increase of tension was investigated as well.

Dynamics and relaxation of large Barkhausen discontinuity in amorphous wires

Domain wall processes (domain wall configuration, propagation, and collapse) in magnetostrictive amorphous wires of the composition Fe/sub 77.5/Si/sub 7.5/B/sub 15/ were investigated. The wires were held under tensile stress (up to 1700 MPa in the case of as-quenched). The domain wall length and normal mobility (or damping) as functions of applied stress were found experimentally and from an ellipsoidal domain model. This allows the losses to be separated into eddy current and spin relaxation contributions. It was demonstrated that the spin relaxation contribution to the total damping parameter becomes dominant with increase of tension and leads to a dramatic decrease of the wall mobility. This is the reason cold-drawn and then tension-heated wires with high residual stress exhibit a much lower mobility in spite of the smaller diameter. The process of domain collapse at a collision of two domain walls is accompanied by a very sharp voltage pulse. It is shown that during the collapse the domain is affected by a growing internal magnetic field connected with an excess of domain surface energy in comparison with magnetostatic energy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

AC magnetic characteristics of cores made from pressed rectangular steel particles

This paper describes a new material and method of processing that yields pressed. compacts magnetically suitable for a variety of AC applications. Small rectangular plain-carbon steel particles ranging in size from 1.5 × 0.25 × 0.15 mm to 3.8 × 0.61 × 0.15 mm are decarburized, individually insulated and uniaxially pressed using typical powder metallurgical techniques. The magnetic properties of compacted ring specimens were measured. The AC losses and permeability of the pressed compacts are strongly dependent upon pressing pressure and particle geometry. Increased compact density lowers the iron losses. Variations of iron loss among the various particle geometries are caused by changes in particle shape anisotropy. At 60 Hz the losses are somewhat higher than those of Conventional carbon steel laminations while at higher frequencies the compact losses are lower. This loss trend is due to the small eddy current contribution to the loss. Permeability also depends upon compact density and particle geometry. Increased density not only lowers the induction within each particle for a fixed overall compact induction, but also decreases the magnetostatic energy within the compacts. Both effects result in the increase in permeability with increased density. The smaller the demagnetizing factor of the individual particles, the higher is the permeability. Iron loss and permeability respond differently to particle geometry; hence, selection of the best particle size will depend upon which of the two characteristics is most important for the particular magnetic circuit involved.

Analysis of eddy-current contribution to the magnetic field in squirrel-cage induction machines

The study of the dynamic behaviour of an asynchronous squirrel-cage machine from the electric and magnetic fields, cannot be carried out if we neglect the consequence of the eddy-currents in rotor bars. In this paper first the electric and magnetic field of an asynchronous machine have been considered, and the diffusion equation has been discretized by means of the finite element method. Taking into account the winding connections and effecting a suitable variable transformation, the machine equation has been written in the input-state- -output form. The achieved model enables to study of the electric and mechanical machine transient-state, also considering the effect of an uneven current distribution in the rotor windings.

Domain wall kinetics in soft ferromagnetic metallic glasses

Domain wall kinetics are studied in glassy iron-base wire and iron-nickel–base ribbon. These materials exhibit high wall mobilities. The wire is examined in a single-wall regime below the nucleation field. Here reversal takes place by propagation of a domain wall of 2.5-cm axial length along the wire. The mobility normal to the wall is 270 cm/sec Oe. In the case of glassy iron-nickel–base ribbon the number of walls taking part in reversal is measured to be two. Using this number, the wall mobility is 1700 cm/sec Oe. The viscosity limiting the wall mobility is partitioned into a (calculated) eddy-current contribution and a spin-relaxation contribution. The latter constitutes about 40% of the total viscosity in the wire and about 50% in the ribbon samples. Gilbert damping constants for these samples, 0.44 (wire) and 0.19 (ribbon), are small compared with similarly obtained values for comparable polycrystalline alloys.

Eddy current linewidth contribution and propagation effects in low resistivity ferrites

Eddy current linewidth contribution and propagation effects in low resistivity ferrites