26 research outputs found
Bias-free spin-wave phase shifter for magnonic logic
A design of a magnonic phase shifter operating without an external bias
magnetic field is proposed. The phase shifter uses a localized collective spin
wave mode propagating along a domain wall "waveguide" in a dipolarly-coupled
magnetic dot array existing in a chessboard antiferromagnetic (CAFM) ground
state. It is demonstrated numerically that remagnetization of a single magnetic
dot adjacent to the domain wall waveguide introduces a controllable phase shift
in the propagating spin wave mode without significant change of the mode
amplitude. It is also demonstrated that a logic XOR gate can be realized in the
same system.Comment: 6 pages, 4 figure
The Numerical Simulation Application for Fire-Tube Boiler Heating Surface Safety Evaluation
The numerical simulation is applied for fire-tube boiler heating surface safety estimation. Thermal processes in an inflatable fire-tube furnace during its emergency operation were simulated using the finite volume method with Euler approximation and the implicit pressure based algorithm. Study results reproduce failures connected with increasing of impasse aerodynamic resistance. The method of these failures prediction is suggested. Simulation has shown that entering the amount of coolant into combustion volume results in burner fan incapability to overcome the impasse resistance of the furnace. The simulation results are visually confirmed during the inspection of emergency boilers
Persistent spin textures in halide perovskites induced by uniaxial stress
Persistent spin textures are highly desirable for applications in spintronics
as they may allow for long carrier spin lifetimes. However, they are also rare
as only four point groups can host such textures, and even for these four
groups, the emergence of persistent spin textures requires a delicate balance
between coupling parameters, which control the strength of spin-momentum
interactions. We use first-principles density functional simulations to predict
the possibility of achieving these desirable spin textures through the
application of uniaxial stress. Hybrid organic-inorganic perovskite MPSnBr
(MP = CHPH) is a ferroelectric semiconductor which exhibits persistent
spin textures in the near to its conduction band minimum and mostly Rashba type
in the vicinity of its valence band maximum. Application of uniaxial stress
leads to the gradual evolution of the valence bands spin textures from mostly
Rashba type to persistent ones under tensile load and to pure Rashba or
persistent ones under compressive load. We also report that the material
exhibits flexibility, rubber-like response, and both positive and negative
piezoelectric constants. Combination of such properties may create
opportunities for a flexible/rubbery spintronic devices
Aluminum anodization in deionized water as electrolyte
Thin oxide films were prepared electrochemically on the aluminum surface using the high-voltage discharge and potentiostatic
methods in deionized water as an electrolyte. The growth of continuous films occurred only at potentials lower than the breakdown
potential. The films obtained by the discharge method are more uniform and can grow to a higher thickness in comparison to
those formed by the potentiostatic mode, as demonstrated by electrochemical impedance spectroscopy (EIS), transmission electron
microscopy (TEM), and scanning Kelvin probe force microscopy (SKPFM). The data herein obtained can be used as a reference to
understand better the properties of the films produced in conventional electrolytes where apart from water other species are present
Prospects for electrical performance tuning in Ca3Co4O9 materials by metallic Fe and Ni particles additions
This work further explores the possibilities for designing the high-temperature electrical
performance of the thermoelectric Ca3Co4O9 phase, by a composite approach involving separate
metallic iron and nickel particles additions, and by employing two different sintering schemes,
capable to promote the controlled interactions between the components, encouraged by our recent
promising results obtained for similar cobalt additions. Iron and nickel were chosen because of
their similarities with cobalt. The maximum power factor value of around 200 µWm−1K−2 at 925 K
was achieved for the composite with the nominal nickel content of 3% vol., processed via the twostep sintering cycle, which provides the highest densification from this work. The effectiveness
of the proposed approach was shown to be strongly dependent on the processing conditions and
added amounts of metallic particles. Although the conventional one-step approach results in Feand Ni-containing composites with the major content of the thermoelectric Ca3Co4O9 phase, their
electrical performance was found to be significantly lower than for the Co-containing analogue,
due to the presence of less-conducting phases and excessive porosity. In contrast, the relatively
high performance of the composite with a nominal nickel content of 3% vol. processed via a
two-step approach is related to the specific microstructural features from this sample, including
minimal porosity and the presence of the Ca2Co2O5 phase, which partially compensate the complete
decomposition of the Ca3Co4O9 matrix. The obtained results demonstrate different pathways to
tailor the phase composition of Ca3Co4O9
-based materials, with a corresponding impact on the
thermoelectric performance, and highlight the necessity of more controllable approaches for the
phase composition tuning, including lower amounts and different morphologies of the dispersed
metallic phases.publishe
Nonreciprocity of spin waves in metallized magnonic crystal
The nonreciprocal properties of spin waves in metallized one-dimensional bi-component magnonic crystal composed of two materials with different magnetizations are investigated numerically. Nonreciprocity leads to the appearance of indirect magnonic band gaps for magnonic crystals with both low and high magnetization contrast. Specific features of the nonreciprocity in low contrast magnonic crystals lead to the appearance of several magnonic band gaps located within the first Brillouin zone for waves propagating along the metallized surface. Analysis of the spatial distribution of dynamic magnetization amplitudes explains the mechanism of dispersion band formation and hybridization between magnonic bands in magnonic crystals with metallization
Geometric frustration in compositionally modulated ferroelectrics
Geometric frustration is a broad phenomenon that results from an intrinsic
incompatibility between some fundamental interactions and the underlying
lattice geometry1-7. Geometric frustration gives rise to new fundamental
phenomena and is known to yield intriguing effects, such as the formation of
exotic states like spin ice, spin liquids and spin glasses1-7. It has also led
to interesting findings of fractional charge quantization and magnetic
monopoles5,6. Geometric frustration related mechanisms have been proposed to
understand the origins of relaxor behavior in some multiferroics, colossal
magnetocapacitive coupling and unusual and novel mechanisms of high Tc
superconductivity1-5. Although geometric frustration has been particularly well
studied in magnetic systems in the last 20 years or so, its manifestation in
the important class formed by ferroelectric materials (that are compounds
exhibiting electric rather than magnetic dipoles) is basically unknown. Here,
we show, via the use of a first-principles-based technique, that
compositionally graded ferroelectrics possess the characteristic "fingerprints"
associated with geometric frustration. These systems have a highly degenerate
energy surface and exhibit original critical phenomena. They further reveal
exotic orderings with novel stripe phases involving complex spatial
organization. These stripes display spiral states, topological defects and
curvature. Compositionally graded ferroelectrics can thus be considered as the
"missing" link that brings ferroelectrics into the broad category of materials
able to exhibit geometric frustration. Our ab-initio calculations allow a deep
microscopic insight into this novel geometrically frustrated system.Comment: 14 pages, 5 Figures;
http://www.nature.com/nature/journal/v470/n7335/full/nature09752.htm