Yoshiko H. Ohashi

Effect of N atom and lattice constant on electronic structures and magnetic properties of Fe16N2 calculated by band structure calculation based on local-density approximation

Band calculations have been performed for iron nitride, Fe16N2, using the self-consistent linearized-augmented-plane-wave (LAPW) method within the framework of the LDA (local-density approximation). The lattice constant dependence on the magnetic properties of Fe16N2 is calculated. Calculations for Fe16N2, which has the same structure as Fe16N2 without N atoms, are also carried out to examine the effect of N atoms. The magnetic moment calculated is much smaller than the giant value observed experimentally as presented in previous work. The lattice constant dependence of the moment can be explained by the magnetovolume effect. The dependence shows that a little difference in the lattice constant does not cause a serious change in the magnetic moment. The calculated results for Fe16X2 show electron transfer between the Fe atoms at different sites and the N atom. The lack of N atoms does not explain the giant magnetic moment of Fe16N2.

Study of giant magnetoresistance in Co/X superlattices (X=Cu, Ru, Rh and Pd) by first-principle band calculation

Abstract First-principle band structure calculation based on linear-muffin-tin-orbital atomic-sphere-approximation method is used to study the giant magnetoresistance (MR) effect and the electronic structure of Co/X superlattices (X=Cu, Ru, Rh and Pd). The MR ratio is estimated as the ratio of the D(eF)vF2 between the anti-parallel and the parallel magnetic configurations, where D(eF) and vF are the density of states at Fermi energy and the Fermi velocity. The non-magnetic layer thickness dependence of the MR ratio is also calculated. These results are in good agreement with experiments.

Effect of Nb addition to Ni and Fe on electronic structure and magnetic properties

Abstract The electronic structure and magnetic properties of fcc NiNb and bcc FeNb alloys within the Nb concentration of 20 at% are studied by band structure calculations based on the Korringa-Kohn-Rostoker coherent-potential approximation method. The results show that niobium has a magnetic moment in Ni and Fe with antiparallel coupling. The density of states of Nb in fcc NiNb and bcc FeNb calculated in the paramagnetic state shows a minimum at the Fermi energy which leads to the antiparallel coupling of Nb. The local magnetic moments of Nb and Ni drop abruptly in fcc NiNb alloy as the Nb concentration increases, although the local magnetic moment of the Nb hardly decreases in bcc FeNb alloy.

Thermal properties of vibrating dislocations

Abstract Using the elastic theory and Green function method, the changes in the vibrational properties of a solid containing vibrating dislocations are studied. Particular, the enhanced specific heat due to dislocations is discussed in detail. Furthermore, the influence of the localized mode created by dislocations is considered.

Phonon scattering by dislocations in LiF crystals

Abstract A theory is presented of the interaction between thermal phonons and a vibrating dislocation. An expression for the relaxation time of the phonon is obtained which is valid in an anisotropic medium. The relaxation time depends on the strength of the imaginary part of the effective mass of the vibrating dislocation. We have calculated numerically this factor for LiF and have found the mode dependence to be very strong. The slow transverse-mode component is about ten times larger than the other mode components. Hence, the slow transverse mode is scattered more strongly than other modes by vibrating dislocations in LiF. Agreement with experimental data is obtained.

Breakdown properties of random systems with distributed conductances

The breakdown problem in a random system is investigated by numerical simulation for a network of distributed conductance The breakdown voltages are studied in the different conductance configurations. The mean breakdown strength shows anomalous size dependence given by ∝1/((ln L )) y for L (the linear dimension of the network). The exponent y depends upon a degree of non-uniformity of the system and gives an information on the critical event of the breakdown. For the case of a comparatively homogeneous network the micro-crack nucleation is the critical event of a breakdown. In such a random resistor network funnel defects act as the appropriate critical defects. On the other hand, in the case of strongly disordered system the critical event in a breakdown is attributed to growth of cracks.

Dynamics of an impurity hydrogen in magnesium

The dynamics of an impurity hydrogen in magnesium is investigated by using the pair potential technique. We have calculated the pair potential between hydrogen and magnesium, taking account of the non-linear screening effects of an impurity hydrogen. By use of it, we have calculated the energy profile for interstitial hydrogen and the force constants between hydrogen and magnesium. As the results of them, it is found that the minimum point of energy is too shallow to localize the interstitial hydrogen, and that the coupling between substitutional hydrogen and the nearest neighbor magnesium ion is very weak.

Characteristic of a Microwave Strip Line Made from YBa2Cu3O7-x Superconductor on Alumina Substrate

Strip lines of high Tc (HTC) superconductor material are made on alumina substrates. Films with a sharp transition temperature of YBaCuO superconductor have been prepared by a printing method with buffer treatment. The attenuation of microwaves travelling on the HTC strip lines was examined by means of the time domain method at 77 K, and the value of the attenuation per meter was found to be 5.5 dB/m around 10 GHz.

Localized mode due to a vibrating dislocation in alkali halides

The mass and the line tension of a vibrating dislocation in alkali halide crystals have been calculated. The results indicate that in LiF a localized mode exists that is due to a vibrating dislocation. In NaCl and KC1 the existence of such a mode is not expected.

Non-Linear Electrical Transport in Silver Sulfide

We have measured the current-voltage characteristics of β-Ag 2 S layer at the liquid-nitrogen temperature. Samples showed that there is the non-linear evoluation of the electrical current. Our experimental results are consistent with Bishops theory treating the interacting Brownian particles in a periodic local potential.