Materials Literature
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Lifetimes of hot electrons in the 1.3--3.2-eV energy range at low index surfaces of Cu((100),(110),(111)) are measured by two-photon time-resolved photoemission spectroscopy with 10 fs resolution. Energy dependence of the lifetimes deviates from the (E-${\mathrm{E}}_{\mathrm{F}}$${)}^{\mathrm{\ensuremath{-}}2}$ functi…
The determination of the magnetic properties of antiferromagnetic Cr alloys requires careful consideration of the influence of the applied magnetic field. In this work we show that alloys of Cr-x at. % V present a Curie–Weiss paramagnetism above the Néel temperature, which is suppressed by a characteristic field HL. S…
NbFeTe 2 is a layered cluster compound in which intra Fe–Fe bond distance is 2.488 Å. The magnetic susceptibilities between 100 and 300 K are fit to Curie–Weiss law with C=1.29 emu K/mol, and θ=+69.2 K. The effective magnetic moment of 3.67 μB per Fe at 300 K corresponding to three unpaired electrons may suggest the f…
An extension to the model of hysteresis has been presented earlier which included the effect of anisotropy in the modeling of the anhysteretic magnetization curves of uniaxially anisotropic single crystalline materials. Further exploration of this extension shown here considers different kinds of crystal anisotropy in…
The MnAl-base permanent magnets continue to loom on the horizon as potentially important technological materials. Marginal enhancement of their technical magnetic properties and improved processing could markedly change the relationship of these materials to the current market. MnAl-base magnets derive their attractiv…
The origin of coercivity in precipitation hardened Sm–Co magnets is investigated. By considering domain-wall pinning at boundary phase and Z phase inhomogenities, it is found that the hexagonal Z phase has no direct influence on the coercivity. The intuitive assumption of plane domain walls made in a recent calculatio…
Bonded neodymium magnets can provide significant size and weight reduction and/or performance enhancement over sintered and, particularly, bonded ferrite permanent magnets and, moreover, provide these benefits at reasonable cost. Primarily for these reasons, these bonded magnets are now used in a wide and growing rang…
FeSe thin films were prepared on GaAs(100) substrate by the selenization of Fe films using molecular-beam epitaxy. FeSe compound thin films were obtained at a substrate temperature above 380 °C. From the depth profiles of Fe and Se in the selenized film measured by Auger electron spectroscopy, it was confirmed that an…
Ferromagnet-insulator-ferromagnet tunnel junctions with one NiMnSb electrode were studied to test the 100% conduction electron spin polarization predicted from band structure calculations performed on this compound. This phenomenon, known as half-metallic ferromagnetism (HMF), should result in significantly larger jun…
CrO 2 films were deposited on Al2O3 and TiO2 by high-pressure decomposition of CrO3. They are metallic, with a residual resistivity ρ0 in the range 0.2–10 μΩ m. The resistivity below Tc varies as ρ0+αT2+βT7/2 as expected for a correlated fully spin-polarized d band. At Tc the resistivity changes slope but the sign rem…
Evidence for variable range hopping (VRH) is presented in resistivity measurements in thin films and bulk samples of different substituted x=0.3 manganese perovskites. The necessity to modify the Mott VRH model is shown and we have developed a model based on magnetic localization hopping, which is used to reproduce te…
Spherical, monodisperse, submicrometer-sized particles in the CoxNi(100−x) system have been synthesized by the polyol process over the whole chemical composition range. These fine particles have been insulated by a chemical treatment in solution by a superficial layer of MnO2. The microwave permeability of these passi…
We report an ab initio calculation of the binding energies and the nature of the excitonic states in the near-gap absorption spectrum of a real solid, ${\mathrm{Li}}_{2}$O. We calculate the ground-state properties using density-functional theory together with soft pseudopotentials. Applying Hedin's GW approximation fo…
Structural changes of tussah (Antheraea pernyi) silk fibroin films induced by heat treatment were studied as a function of the treatment temperature in the range 200–250°C. The DSC curve of tussah films with α-helix molecular conformation displayed characteristic endo and exo peaks at 216 and 226°C, respectively. Thes…
The effect of Fe doping (<20%) on the Mn site in the ferromagnetic (x=0.37) and the antiferromagnetic (x=0.53) phases of La1−xCaxMnO3 has been studied. Upon doping, no appreciable structure changes have been found in either series. However, conduction and ferromagnetism have been consistently suppressed by Fe d…
A probable heterodiamond ${\mathrm{BC}}_{2}$N structure that can be obtained from compression of graphitic ${\mathrm{BC}}_{2}$N at low temperature is proposed using first-principles calculations. The structure consists of a rhombohedral atomic arrangement and has a large bulk modulus comparable to that of diamond as w…
Permanent magnets play a vital role in modern society as a component in a wide range of devices utilized by many industries and consumers. In 1995, the world production of permanent magnets was estimated to be valued at $3.6 billion and growing at an annual rate of 12%. Bonded permanent magnets are the fastest growing…
Within the framework of a partial-density approach, the confinement of vibrations in spherical Si nanocrystals is studied and the Raman frequency shifts of Si spheres with different sizes are derived based on the Raman spectra obtained by a bond-polarizability model. The results obtained by the bond-polarizability mod…
The attributes of electron field emission from disordered matrix arrays of carbon nanotubes are studied and found to be quite reproducible in spite of the disorder, density, and quality variations from sample to sample. At low applied electric fields, the electron field emission current-voltage characteristics qualita…
In the substitutionally disordered narrow-gap semiconductor Pb_{1-x}Ge_xTe, a finite-temperature cubic-rhombohedral transition appears above a critical concentration $x \approx 0.005$. As a first step towards a first-principles investigation of this transition in the disordered system, a (hypothetical) ordered cubic P…