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$_3$ (MP = CH$_3$PH$_3$) 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