Spin-orbit-induced spin-density wave in a quantum wire

We present analysis of the interacting quantum wire problem in the presence of magnetic field and spin-orbit interaction. We show that an interesting interplay of Zeeman and spin-orbit terms, facilitated by the electron-electron interaction, results in the spin-density wave state when the magnetic field and spin-orbit axes are orthogonal. This strongly affects charge transport through the wire: With the spin-density wave stabilized, single-particle backscattering off a nonmagnetic impurity becomes irrelevant. The sensitivity of the effect to the direction of the magnetic field can be used for experimental verification of this proposal.     

Direct evidence for reversible diffusional phase change in nanometer-sized alloy particles

Solid solubility in isolated nanometer-sized particles has been studied by in situ transmission electron microscopy using alloy particles in the Pb-Sn binary system. In approximately 17-nm-sized particles of a lead-56 at. % Sn solid solution, a phase change from a single phase of the lead solid solution to two phases, a lead solid solution and a tin-solid solution, takes place when the temperature is reduced from 110 degrees C to room temperature (RT). Furthermore, it is confirmed that this phase change could occur rather reversibly when the temperature is cyclically changed between 110 degrees C and RT. This observation provides direct evidence for reversible diffusional phase change in nanometer-sized alloy particles. It seems safe to conclude that the solubility limit of tin in lead is higher than 56 at. % at 110 degrees C, which is almost 5 times higher than the solubility limit of tin in bulk lead (i.e., 10 at. %).     

Direct evidence for thermal mechanism of plasma influence on shock wave propagation

Shock wave propagation through a glow discharge is studied by a double beam laser Schlieren method. A pulsed discharge is used to separate electron and other plasma related phenomena from thermal effects. The results prove the pure thermal nature of the influence of a plasma on a shock wave.     

Incommensurate spin-density wave order in electron-doped BaFe2 As2 superconductors

Neutron diffraction studies of Ba(Fe(1-x)Co(x))(2)As)(2) reveal that commensurate antiferromagnetic order gives way to incommensurate magnetic order for Co compositions between 0.056 < x < 0.06. The incommensurability has the form of a small transverse splitting (0, ± ε, 0) from the commensurate antiferromagnetic propagation vector Q(AFM) = (1,0,1) (in orthorhombic notation) where ε ≈ 0.02-0.03 and is composition dependent. The results are consistent with the formation of a spin-density wave driven by Fermi surface nesting of electron and hole pockets and confirm the itinerant nature of magnetism in the iron arsenide superconductors.     

Anti-Invar properties and magnetic order in fcc Fe-Ni-C alloy

Anti-Invar effect was revealed in the fcc Fe-25.3%Ni-0.73%C (wt%) alloy, which demonstrates high values of thermal expansion coefficient (TEC) (15-21)×10⁻⁶ K⁻¹ accompanied by almost temperature-insensitive behavior in temperature range of 122-525 K. Alloying with carbon considerably expanded the low temperature range of anti-Invar behavior in fcc Fe-Ni-based alloy. The Curie temperature of the alloy T_C=195 K was determined on measurements of temperature dependences of magnetic susceptibility and saturation magnetization. The Mössbauer and small-angle neutron scattering (SANS) experiments on the fcc Fe-25.3%Ni-(0.73-0.78)%C alloys with the varying temperatures below and above the Curie point and in external magnetic field of 1.5-5 T were conducted. Low value of the Debye temperature Θ_D=180 K was estimated using the temperature dependence of the integral intensity of Mössbauer spectra for specified temperature range. The inequality B_eff=(0.7-0.9)B_ext was obtained in external field Mössbauer measurement that points to antiferromagnetically coupled Fe atoms, which have a tendency to align their spins perpendicular to B_ext. Nano length scale magnetic inhomogeneities nearby and far above T_C were revealed, which assumed that it is caused by mixed antiferromagnetically and ferromagnetically coupled Fe atom spins. The anti-Invar behavior of Fe-Ni-C alloy is explained in terms of evolution of magnetic order with changing temperature resulting from thermally varied interspin interaction and decreasing stiffness of interatomic bond.     

Interface-induced states with an incommensurate spin-density wave in Fe/Cr-type multilayers

A model is proposed for magnetic ordering in Fe/Cr-type multilayers substantially above the Néel temperature of bulk chromium. Redistribution of the charge (and, hence, spin) density near the Fe/Cr interfaces gives rise to the formation of an essentially inhomogeneous spin-density-wave (SDW) state in the chromium spacer. The spatial structure of the antiferromagnetic order parameter in thick spacers is described. The SDW contribution to the effective exchange coupling between the moments in adjacent iron layers is calculated. The data obtained are used in the interpretation of experimental data on the tunneling spectroscopy of trilayers and neutron diffraction from Fe/Cr superlattices.     

Calculation of enhancement factors for solute diffusion in the fcc dilute random alloy

In this paper, we address the enhancement of solute diffusion by solute addition. We focus on the little studied kinetic effect leading to solute enhancement arising from the kinetics of the encounter of a solute atom with a vacancy in the presence of other solute atoms. The study complements an earlier study by two of the present authors of the enhancement of the solvent diffusivity. In the present paper, the fcc random alloy model is employed at the dilute limit. We employ Monte Carlo techniques to calculate the solute diffusion enhancement factors B ₁ and B ₂. Solute correlation factors, upon which the enhancement factors rely in this model, are calculated to a very high precision using long runs and averaging over a very large number of atoms. There is fair agreement with the kinetic treatments of Manning and of Holdsworth and Elliott, and excellent agreement with the self-consistent theory of Moleko et al.     

Uniform spin wave modes in antiferromagnetic nanoparticles with uncompensated moments

In magnetic nanoparticles the uniform precession (q = 0 spin wave) mode gives the predominant contribution to the magnetic excitations. We have calculated the energy of the uniform mode in antiferromagnetic nanoparticles with uncompensated magnetic moments, using the coherent potential approximation. In the presence of uncompensated moments, an antiferromagnetic nanoparticle must be considered as a kind of a ferrimagnet. Two magnetic anisotropy terms are considered, a planar term confining the spins to the basal plane, and an axial term determining an easy axis in this plane. Excitation energies are calculated for various combinations of these two anisotropy terms, ranging from the simple uniaxial case to the planar case with a strong out-of-plane anisotropy. In the simple uniaxial case, the uncompensated moment has a large influence on the excitation energy, but in the planar case it is much less important. The calculations explain recent neutron scattering measurements on nanoparticles of antiferromagnetic α-Fe₂O₃ and NiO.     

Spin wave amplification in antiferromagnetic semiconductors stimulated by infrared laser field

The spin wave excitation induced by infrared laser radiation in antiferromagnetic semiconductors is considered. By considering that several photons from the IR laser field can be involved in the electronic transition a kinetic equation for the magnon population is calculated from which the magnon excitation rate is calculated. It is found that under certain conditions the excitation rate may become greater than the magnon relaxation rate and the magnon system can reach instability. An application is made for the antiferromagnetic semiconductor EuTe.     

Direct evidence for homonuclear bonds in amorphous SiC

The Raman Spectra of carbon-deficient sputtered amorphous SiC films contain an intense band centered at 1442 cm^?1. This band is attributed to the presence of C-C bonds. Similarly a peak at ～508 cm^?1 is attributed to Si-Si bonds. The depolarization spectrum was found to be constant at $\text{?(Δ}\text{v}\text{?}\text{) = 0.32 ± 0.03}$ for $\text{0 < Δ}\text{v}\text{?}\text{< 1800}\text{cm}{}^{\mathrm{?1}}$. Our results indicate a degree of compositional disorder which prevents an identification of the observed like-atom bonds with those predicted by a modified Polk model.