Modeling of Gravitational Separation By the Method of Smoothed Particles Hydrodynamics (SPH)

The article deals with the peculiarities of solving the problem of numerical simulation of gravity separation of dispersed particles. A simulation model is created by using the Monte Carlo method, in which the ‘first principles’ (elementary particles) are particles of the charge and reaction products. The object-oriented language ActionScript 3.0 was chosen as the programming language. At the same time, the most difficult(computational) task was to find neighbors (complexity N2 ). In this article, the comparison analysis of the improved algorithm of neighbors search of complexity (2⋅N⋅k) with standard neighbors search is given; the object of comparison is the quantity of the displayed particles moving in real time. Keywords: modeling of flows, gravity separator, the Monte Carlo method, smoothed particles, complexity of the algorithm, neighbors searc

Inverse Tunneling Magnetoresistance in nanoscale Magnetic Tunnel Junctions

We report on our theoretical study of the inverse TMR effect in the spin polarized transport through a narrow channel. In the weak tunneling limit, we find the ordinary positive TMR. The TMR changes its sign as the transmission probability becomes large close to a unity. Our results might be relevant to the magnetic tunnel junction with a pinhole or a quantum point contact.Comment: 11 pages, 4 figures, To be published in Phys. Rev. B (in press

Interface states in CoFe2O4 spin-filter tunnel junctions

Spin-filter tunneling is a promising way to generate highly spin-polarized current, a key component for spintronics applications. In this work we explore the tunneling conductance across the spin-filter material CoFe2O4 interfaced with Au electrodes, a geometry which provides nearly perfect lattice matching at the CoFe2O4/Au(001) interface. Using density functional theory calculations we demonstrate that interface states play a decisive role in controlling the transport spin polarization in this tunnel junction. For a realistic CoFe2O4 barrier thickness, we predict a tunneling spin polarization of about -60%. We show that this value is lower than what is expected based solely on considerations of the spin-polarized band structure of CoFe2O4, and therefore that these interface states can play a detrimental role. We argue this is a rather general feature of ferrimagnetic ferrites and could make an important impact on spin-filter tunneling applications.Comment: 5 pages, 4 Figures plus 1 page supplemen

Suppression of Octahedral Tilts and Associated Changes of Electronic Properties at Epitaxial Oxide Heterostructure Interfaces

Epitaxial oxide interfaces with broken translational symmetry have emerged as a central paradigm behind the novel behaviors of oxide superlattices. Here, we use scanning transmission electron microscopy to demonstrate a direct, quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen octahedral rotations across the BiFeO3-La0.7Sr0.3MnO3 interface to elucidate how the change of crystal symmetry is accommodated. Combined with low-loss electron energy loss spectroscopy imaging, we demonstrate a mesoscopic antiferrodistortive phase transition and elucidate associated changes in electronic properties in a thin layer directly adjacent to the interface

Spectral analysis of Kepler SPB and Beta Cep candidate stars

We determine the fundamental parameters of SPB and Beta Cep candidate stars observed by the Kepler satellite mission and estimate the expected types of non-radial pulsators by comparing newly obtained high-resolution spectra with synthetic spectra computed on a grid of stellar parameters assuming LTE and check for NLTE effects for the hottest stars. For comparison, we determine Teff independently from fitting the spectral energy distribution of the stars obtained from the available photometry. We determine Teff, log(g), micro-turbulent velocity, vsin(i), metallicity, and elemental abundance for 14 of the 16 candidate stars, two of the stars are spectroscopic binaries. No significant influence of NLTE effects on the results could be found. For hot stars, we find systematic deviations of the determined effective temperatures from those given in the Kepler Input Catalogue. The deviations are confirmed by the results obtained from ground-based photometry. Five stars show reduced metallicity, two stars are He-strong, one is He-weak, and one is Si-strong. Two of the stars could be Beta Cep/SPB hybrid pulsators, four SPB pulsators, and five more stars are located close to the borders of the SPB instability region.Comment: 10 pages, 10 figures, 10 table

Triangular hysteresis loops in the spin-rotation region of orthoferrites

Suggested theory qualitatively explains the shapes of the hysteresis loops in orthoferrites within the temperature interval of the magnetic reorientation transition. Triangular loops result from the strong temperature dependence of both the magnetic moment and the magnetic domain wall structure

Colossal Magnetoresistance by Avoiding a Ferromagnetic State in the Mott System Ca3Ru2O7

Transport and magnetic studies of Ca3Ru2O7 for temperatures ranging from 0.4 K to 56 K and magnetic fields, B, up to 45 T leads to strikingly different behavior when the field is applied along the different crystal axes. A ferromagnetic (FM) state with full spin polarization is achieved for B||a-axis, but colossal magnetoresistance is realized only for B||b-axis. For B||c-axis, Shubnikov-de Haas oscillations are observed and followed by a less resistive state than for B||a. Hence, in contrast to standard colossal magnetoresistive materials, the FM phase is the least favorable for electron hopping. These properties together with highly unusual spin-charge-lattice coupling near the Mott transition (48 K) are driven by the orbital degrees of freedom.Comment: 15 pages including 3 figure

Re-orientation Transition in Molecular Thin Films: Potts Model with Dipolar Interaction

We study the low-temperature behavior and the phase transition of a thin film by Monte Carlo simulation. The thin film has a simple cubic lattice structure where each site is occupied by a Potts parameter which indicates the molecular orientation of the site. We take only three molecular orientations in this paper which correspond to the 3-state Potts model. The Hamiltonian of the system includes: (i) the exchange interaction $J_{ij}$ between nearest-neighbor sites $i$ and $j$ (ii) the long-range dipolar interaction of amplitude $D$ truncated at a cutoff distance $r_c$ (iii) a single-ion perpendicular anisotropy of amplitude $A$. We allow $J_{ij} =J_s$ between surface spins, and $J_{ij}=J$ otherwise. We show that the ground state depends on the the ratio $D/A$ and $r_c$. For a single layer, for a given $A$, there is a critical value $D_c$ below (above) which the ground-state (GS) configuration of molecular axes is perpendicular (parallel) to the film surface. When the temperature $T$ is increased, a re-orientation transition occurs near $D_c$: the low-$T$ in-plane ordering undergoes a transition to the perpendicular ordering at a finite $T$, below the transition to the paramagnetic phase. The same phenomenon is observed in the case of a film with a thickness. We show that the surface phase transition can occur below or above the bulk transition depending on the ratio $J_s/J$. Surface and bulk order parameters as well as other physical quantities are shown and discussed.Comment: 7 pages, 11 figures, submitted for publicatio

Frustration Effects in Antiferromagnetic FCC Heisenberg Films

We study the effects of frustration in an antiferromagnetic film of FCC lattice with Heisenberg spin model including an Ising-like anisotropy. Monte Carlo (MC) simulations have been used to study thermodynamic properties of the film. We show that the presence of the surface reduces the ground state (GS) degeneracy found in the bulk. The GS is shown to depend on the surface in-plane interaction $J_s$ with a critical value at which ordering of type I coexists with ordering of type II. Near this value a reentrant phase is found. Various physical quantities such as layer magnetizations and layer susceptibilities are shown and discussed. The nature of the phase transition is also studied by histogram technique. We have also used the Green's function (GF) method for the quantum counterpart model. The results at low-$T$ show interesting effects of quantum fluctuations. Results obtained by the GF method at high $T$ are compared to those of MC simulations. A good agreement is observed.Comment: 11 pages, 19 figures, submitted to J. Phys.: Condensed Matte