23 research outputs found
First-principles calculations atomic structure and elastic properties of Ti-Nb alloys
Elastic properties of Ti based \beta-alloy were studied by the method of the
model structure first principle calculations. Concentrational dependence of
Young modulus for the binary \beta-alloy Ti-Nb was discovered. It is shown that
peculiarities visible at 15-18% concentrations can be related to the different
Nb atoms distribution. Detailed comparison of the calculation results with the
measurement results was done. Young modulus for the set of the ordered
structures with different Nb atoms location, which simulate triple \beta-alloys
Ti-29.7%Zr-18.5%Nb and Ti-51.8%Zr-18.5%Nb have been calculated. The results of
these calculations allowed us to suggest the concentration region for
single-phase ternary \beta-phase alloys possessing low values of Young's
modulus
Ab-initio modeling of the short range order in Fe-N and Fe-C austenitic alloys
In the present paper, we have studied atomic structure of nitrogenous
austenite. High precision ab-initio calculation was utilized for the
calculation of the pair potentials of interatomic interactions N-N in FCC Fe
lattice. These potentials were used for the Monte Carlo modeling of the short
range order in the Fe-N system. It was discovered that in FCC Fe lattice,
nitrogen atoms might be partially ordered. In this case, atomic structure of
nitrogenous austenite is characterized by availability of the Fe6N phase with
the short range order over the N atoms located in the third coordination
sphere
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
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
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