Influence of carbon and nitrogen on electronic structure and hyperfine interactions in fcc iron-based alloys

Carbon and nitrogen austenites, modeled by Fe8N and Fe8C superstructures are studied by full-potential LAPW method. Structure parameters, electronic and magnetic properties as well as hyperfine interaction parameters are obtained. Calculations prove that Fe-C austenite can be successfully modeled by ordered Fe8C superstructure. The results show that chemical Fe-C bond in Fe8C has higher covalent part than in Fe8N. Detailed analysis of electric field gradient formation for both systems is performed. The calculation of electric field gradient allow us to carry out a good interpretation of Moessbauer spectra for Fe-C and Fe-N systems.Comment: 8 pages, 3 figures, IOP-style LaTeX, submitted to J. Phys. Condens. Matte

Temperature-controlled interlayer exchange coupling in strong/weak ferromagnetic multilayers: a thermo-magnetic Curie-switch

We investigate a novel type of interlayer exchange coupling based on driving a strong/weak/strong ferromagnetic tri-layer through the Curie point of the weakly ferromagnetic spacer, with the exchange coupling between the strongly ferromagnetic outer layers that can be switched, on and off, or varied continuously in magnitude by controlling the temperature of the material. We use Ni-Cu alloy of varied composition as the spacer material and model the effects of proximity-induced magnetism and the interlayer exchange coupling through the spacer from first principles, taking into account not only thermal spin-disorder but also the dependence of the atomic moment of Ni on the nearest-neighbor concentration of the non-magnetic Cu. We propose and demonstrate a gradient-composition spacer, with a lower Ni-concentration at the interfaces, for greatly improved effective-exchange uniformity and significantly improved thermo-magnetic switching in the structure. The reported magnetic multilayer materials can form the base for a variety of novel magnetic devices, such as sensors, oscillators, and memory elements based on thermo-magnetic Curie-switching in the device.Comment: 15 pages, 5 figure

On chemical bonding of Helium with hcp-Beryllium

Chemical inertness is the key property of helium determining its solubility, distribution and accumulation kinetics in metals. Against all expectations, our ab initio calculations show a substantial chemical bonding between He and Be atoms in the hcp-Be matrix when He occupies a non-symmetric position in a basal plane.Comment: Revised version of manuscript, 4 pages, 4 figure

The origin of the E+ transition in GaAsN alloys

Optical properties of GaAsN system with nitrogen concentrations in the range of 0.9-3.7% are studied by full-potential LAPW method in a supercell approach. The E+ transition is identified by calculating the imaginary part of the dielectric function. The evolution of the energy of this transition with nitrogen concentration is studied and the origin of this transition is identified by analyzing the contributions to the dielectric function from different band combinations. The L_1c-derived states are shown to play an important role in the formation of the E+ transition, which was also suggested by recent experiments. At the same time the nitrogen-induced modification of the first conduction band of the host compound are also found to contribute significantly to the E+ transition. Further, the study of several model supercells demonstrated the significant influence of the nitrogen potential on the optical properties of the GaAsN system.Comment: 5 pages, 3 figure

Erosion of multi-arc cathodes

Translated from Russian (Reports of the Inst. of Theoretical and Applied Mechanics, Russian Academy of Science, Novosibirsk (RU), 1997)Available from British Library Document Supply Centre-DSC:9023.190(VR-Trans--8417)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Erosion of multi-arc cathodes

Translated from Russian (Proceedings of Thermal Plasma 98, Institute of Thermophysics, Russian Academy of Sciences, Novosibirsk, 1998)Available from British Library Document Supply Centre-DSC:9023.190(9393)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Energy characteristics of electric arc heaters for tetrafluoromethane

Translated from Russian (Proceedings of Thermal Plasma 98, Institute of Thermophysics, Russian Academy of Sciences, Novosibirsk, 1998)Available from British Library Document Supply Centre-DSC:9023.190(9392)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo