Materials Literature
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The Brown paradox1 concerns an order of magnitude discrepancy between micromagnetic theory and experiments: the theoretical nucleation field for an elongated iron specimen is −500 Oe whereas the measured value for high-quality iron whiskers is about 0.1 Oe. It is a fairly widespread view that the paradox may be resolv…
A generalization of the vector Preisach hysteresis model is proposed. This new vector hysteresis model represents a larger class of hysteresis nonlinearities than either the Stoner-Wohlfarth model or the previously developed vector Preisach model. To demonstrate this fact, it will be shown that the Stoner-Wohlfarth mo…
PNb 9 O 25 cristallise dans I4/m avec a=15,639, c=3,8317 A, Z=2; affinement jusqu'a R=0,031. Le reseau est compose de colonnes 3×3×∞ du type ReO 3 . Chaque colonne possede des sommets communs avec les quatre colonnes voisines et des cotes communs avec les tetraedres PO 4
The temperature dependence of the magnetic susceptibility for 1.5<T<300 K, the field dependence of the magnetization M(H), for 0<H<23 T and 1.5<T<15 K, and the temperature dependence of the heat capacity C(T), for 5<T<95 K are reported for the insulating distorte…
A new form for the classical Preisach model of hysteresis which gives the decomposition of this model into reversible and irreversible components is derived. This form reveals that the classical Preisach model does describe (to a certain extent) reversible properties of hysteresis nonlinearities. It is also shown that…
We have explored the impact of low-level Cu additions on the magnetic properties of melt-spun Nd-Fe-B ribbons. The addition of 0.5 at. % Cu enhances the intrinsic coercivity as much as 30% over that of Cu-free materials. Transmission electron microscopy analyses demonstrate that Cu segregates preferentially to the int…
In general, the stoichiometry of melt-spun ribbons and subsequent hot-worked Nd-Fe-B magnets derives from the composition of the starting ingot. We have shown, however, that it is possible to introduce small amounts of powdered metals into the ribbons after the ingot has been melt spun. Many elements, when mixed with…
6.5% Si steel is widely known as an excellent soft magnetic material because its magnetostriction is nearly zero. The ac magnetic properties and magnetostriction of 6.5% Si steel sheet were evaluated and compared with those of conventional 3% Si steel sheet. From these data, this sheet is considered to be one of the b…
There has been limited work on the effects of alloying elements on the properties of hot-worked anisotropic magnets. The coercivity mechanisms for sintered and rapidly solidified Nd-Fe-B magnets are different, and additives can have different effects on magnetic properties. The present study was conducted to clarify t…
By numerical simulations treating the motion of a charged soliton in polyacetylene, we analyze the width of a moving soliton. The motion of the soliton is induced by applying an electric field as in the previous work. The soliton width is estimated by two methods; one is from the excess charge density profile and the…
We discuss a generalization of the Preisach model, based on the assumption that each point (α,β) of the Preisach plane corresponds to a small correlation region of the system cross section, inside which magnetic flux reverses at a rate Φ̇ ∝ Ha − α (or Ha − β) when the applied field Ha exceeds the threshold α (or β). W…
The powerful magnet materials based on rare earth (R) and magnetic 3d metals (M=Fe,Co) exhibit a large affinity to absorb hydrogen. Hydrides of the anisotropic materials R2M17 and R2M14X with X=B, C, and RM12 with M=Fe1−xM′x, have been systematically investigated. First, the impact on the fundamental properties (struc…
Subdomain size superparamagnetic particles of Mn-Zn ferrites, having a narrow particle size distribution (peaked around 10 nm) were prepared under mild hydrothermal conditions. High densities (≳99.5%) have been obtained upon sintering these green ferrite powders at relatively low temperatures (∼1000 °C), without the u…
The corrosion mechanism of Nd-Fe-B sintered magnets has been investigated. A correlation between the lifetime of epoxy-coated magnets in a humidity test (80 °C, 90% RH) and the rate of weight loss (ΔW/Δt) of the bare magnets in the pressure cooker test (PCT: 125 °C; 85% RH; 2 atm) has been established. In this system,…
The power loss of Mn-Zn ferrites and its dependency on the microstructural factors have been investigated. The power loss was found to be lowered due to the formation of a high-electrical-resistive boundary layers, which is accomplished by an addition of specific refractory oxides, which are concentrated on the grain…
The photovoltaic characteristics of optimized iodine-doped thin-film sandwich cells of the structure Al/Al2O3/magnesium tetraphenylporphyrin/Au, fabricated and tested under high vacuum, are reported. The action spectra of the short-circuit photocurrent show that only light absorbed near the Al-Al2O3 electrode, to a de…
Chemical and electronic properties of polypyrrole films are investigated for different doping levels using x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy, and high-resolution electron-energy-loss spectroscopy. The XPS results give evidence for instabilities in perchlorate-doped polypyrr…
The influence of an attractive interparticle potential on the rheology of a sterically stabilized silica dispersion was investigated. Using a marginal solvent, there was an effective attraction between the particles which depended on the temperature. Three experiments in which different properties of the dispersion we…
The chemical nature of the nitrogens corresponding to various intrinsic redox states of polypyrrole (PPY) and polyaniline (PAN) has been critically compared using x-ray photoelectron spectroscopy (XPS) as a primary tool. Proton modifications of nitrogens in PPY give rise to a number of intrinsic redox states analogous…
Amorphous transition-metal boron (TM-B) alloy particles can be prepared by chemical reduction of TM ions by borohydride in aqueous solutions. ln the last few years systematic studies of the parameters which control the composition, and, in turn, many of the properties of the alloy particles, have been performed and ar…