Materials Literature
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Ni–Co ferrite has been studied with Mössbauer spectroscopy and x-ray diffraction. The crystal structure for this system is spinel, and the lattice constant is in accord with Vegard’s law. The Mössbauer spectra consist of two six-line patterns corresponding to Fe3+ at the tetrahedral (A) and octahedral (B) sites. The N…
A thin electromagnetic wave absorber has been investigated; it is composed of hexagonal ferrite and retains high permeability even in the gigahertz-range. The grid-type wave absorber composed of the hexagonal ferrite was examined to broaden the bandwidth in a gigahertz-range by introducing free space in the direction…
Anisotropic Nd–Fe–B magnet powders can be produced by the hydrogenationdecomposition-desorption-recombination (HDDR) process from Nd–Fe–B–Co–M (M=Ga, Zr, Nb, Hf, and Ta) alloys. The present status of those HDDR powders and the bonded magnets made from them are reviewed with regards to the powder particle size dependen…
The microstructure and electrical properties of tin-doped indium oxide thin films crystallized under the action of a temperature gradient are compared with those of films prepared under uniform temperature. This zone-confining process, coupled with slow deposition rates, causes preferential segregation of dopants from…
The dissolution mechanism of rubbery polymers was analyzed by dividing the penetrant concentration field into three regimes that delineate three distinctly different transport processes. The solvent penetration into the rubbery polymer was assumed to be Fickian. The mode of mobility of the polymer chains was shown to…
Field emission of electrons from boron- and nitrogen-doped diamond is compared. Emission from boron-doped diamond requires vacuum electric fields of 20–50 V μm−1, while nitrogen-doped, type Ib diamond requires fields of 0–1 V μm−1. Since boron-doped diamond is very conductive, very little voltage drop occurs in the di…
Modifications of the magnetic properties of a nonoriented 3% SiFe alloy with plastic strains are reported. The samples have been tested along rolling and transverse directions lying in the sheet plane by means of a suitable experimental system of measurements using a 50 Hz sinusoidal magnetic field. The magnetic prope…
Optical absorption curves for nominally pure and Ce 3+ doped single crystals of Y 3 Al 5 O 12 (YAG) have been measured in the region of 5 eV–7 eV at 292 K, 78 K and 10 K. The parameters of the Urbach rule have been determined referring to those optical absorption curves which are believed to be the fundamental absorpt…
The Jiles–Atherton theory is based on considerations of the dependence of energy dissipation within a magnetic material resulting from changes in its magnetization. The algorithm based on the theory yields five computed model parameters, MS, a, α, k, and c, which represent the saturation magnetization, the effective d…
Various processing routes for making permanent magnets based on interstitially modified Sm2Fe17 have been recently developed. Zn bonding of coarse grained Sm2Fe17N3 gives coercivities μ0JHc as high as 2.2 T. Effective methods to prepare highly coercive Sm2Fe17N3 powders for polymer bonding are mechanical alloying and…
The molecular characteristics which determine the melting points of high polymer crystals are considered, and it is shown that the properties of monomeric crystals often throw light on those of the polymers. The principal factors controlling melting points appear to be molar cohesion energy (of the whole molecule for…
The combination of chemical composition and microstructure of cast alloy has been found to be critical to the performance of NdFeB sintered magnets. Maximizing the amount of Nd2Fe14B phase (or minimizing the amount of secondary phase) by reducing the Nd content more closely to the stoichiometric composition appears to…
Resonant photoelectron spectroscopy studies have been performed on the NiO valence band at photon energies corresponding to the Ni $2p$,$3p$,and O $1s$ absorption thresholds. Strong resonances are seen in the vicinity of the Ni $2p$ threshold, which confirm earlier conclusions from the weaker resonances seen at the Ni…
Diffusion of penetrants through polymers often does not follow the standard Fickian model. Such anomalous behavior can cause difficulty when designing polymer networks for specific uses. One type of non-Fickian behavior that results is so-called case II diffusion, where Fickian-like fronts initially move like √t with…
A model for the radiation-induced production of defects in amorphous insulators is proposed. It is shown that an irreversible creation of defects from network sites follows power law kinetics, and a reversible activation of precursor sites follows Kohlrausch kinetics. Electron spin resonance was used to measure the co…
Although the production and applications of NdFeB magnets have increased enormously in the last decade because of their outstanding magnetic properties at room temperature, some applications were limited because of poor thermal stability and corrosion resistance. To address these problems, there have been many efforts…
We have attempted to optimize the values of the giant magnetoresistance in symmetric spin valves of the type NiO/Co/Cu/Co/Cu/Co/NiO (achieving 23.4%) and in bottom spin valves of the type Co/Cu/Co/NiO (achieving 17.0%), the largest values ever reported for such structures. The key elements in this achievement are impr…
Hyperbranched polyurethanes, with varying oligoethyleneoxy spacer segments between the branching points, have been synthesized by a one-pot approach starting from the appropriately designed carbonyl azide that incorporates the different spacer segments. The structures of monomers and polymers were confirmed by IR and…
Record values for high Hall mobility and for low compensation ratio of boron doped diamond by ion implantation are reported. These are achieved, following the suggestion by Prins, by low dose Boron implantation into cold diamond (−97 °C) and in situ rapid heating (1050 °C for 10 min) and by a further anneal at higher…
The structural and magnetic properties of (R,Zr)(Fe,Co)10(R=Nd,Sm) prepared by the rapid-quenching method have been investigated. The presence of zirconium makes it possible to realize a TbCu7-type crystal structure with a high c/a ratio of more than 0.87, while the same crystal structure has a c/a ratio of just 0.84–…