arXiv subjects

Maciej Krawczyk

Publications and source records attributed to Maciej Krawczyk.

59 records · Page 4Linked to original sources

arXiv2017

All-Angle Collimation for Spin Waves

We studied the effect of collimation for monochromatic beams of spin waves, resulting from the refraction at the interface separating two magnetic half-planes. The collimation was observed in broad range of the angles of ncidence for homogenous Co and Py half-planes, due to significant intrinsic anisotropy of spin wave propagation in these materials. The effect exists for the sample saturated by in plane magnetic field tangential to the interface. The collimation for all possible angles of incidence was found in the system where the incident spin wave is refracted on the interface between homogeneous and periodically patterned layers of YIG. The refraction was investigated by the analysis of isofrequency dispersion contours of both pairs materials, i.e., uniform YIG/patterned YIG and Co/Py, which are calculated with the aid of the plane wave method. Besides, the refraction in Co/Py system was studied using micromagnetic simulations.

cond-mat.mes-hall↗

arXiv2017

All-Dielectric Metasurfaces Based on Cross-Shaped Resonators for Color Pixels with Extended Gamut

Printing technology based on plasmonic structures has many advantages over pigment based color printing such as high resolution, ultra-compact size and low power consumption. However, due to high losses and broad resonance behavior of metals in the visible spectrum, it becomes challenging to produce well-defined colors. Here, we investigate cross-shaped dielectric nanoresonators which enable high quality resonance in the visible spectral regime and, hence, high quality colors. We numerically predict and experimentally demonstrate that the proposed all-dielectric nanostructures exhibit high quality colors with selective wavelengths, in particular, due to lower losses as compared to metal based plasmonic filters. This results in fundamental colors (RGB) with high hue and saturation. We further show that a large gamut of colors can be achieved by selecting the appropriate length and width of individual $Si$ nanoantennas. Moreover, the proposed all-dielectric metasurface based color filters can be integrated with the well matured fabrication technology of electronic devices.

physics.optics↗

arXiv2017

Spin waves in periodic antidot waveguide of complex base

We consider the planar magnonic waveguide with a periodic sequence of antidots forming zig-zag pattern, where two neighboring antidots are shifted towards the opposite edges of the waveguide. This system has a complex base with two antidots in one unit cell. The Brillouin zone is here two-times narrower than the Brillouin zone for the waveguide without displacement of antidots. We have shown that for dispersion relation folded into narrower Brillouin zone, new frequency gap can be opened and their width can be controlled by the shift of the antidots. We found that, the different strength of spin wave pinning at the edges of the periodic waveguide (and their antidots)determines the dependence of the width of gap on the shift of antidots. For the systems with completely free or ideally pinned magnetization, these dependencies are qualitatively different. We have found an optimum shift of antidot for maximzing the width of the gap for the system with pinned magnetization. More interestingly, we notice that for this kind of geometry of the structure, majority of the modes are doubly degenerate at the edge of Brillouin zone and have a finite group velocity at the very close vicinity of the edge of Brillouin zone, for larger values of antidot shift. This empowers us to design magnonic waveguide to steer the spin waves.

cond-mat.mes-hall↗

arXiv2016

Spin-Wave Spectrum in Magnetic Nanodot with Continuous Transition between Vortex, Bloch-type Skyrmion and Néel-type Skyrmion States

We study spin-wave excitations in a circular ferromagnetic nanodot in different inhomogeneous, topologically non-trivial magnetization states, specifically, vortex and skyrmion states. Gradual change in the strength of the out-of-plane magnetic anisotropy and the Dzyaloshinskii-Moriya exchange interaction leads to continuous phase transitions between different stable magnetic configurations and allows for mapping of dynamic spin modes in and between the vortex, Bloch-type skyrmion and Néel-type skyrmion states. Our study elucidates the connections between gyrotropic modes, azimuthal spin waves and breathing modes in various stable magnetization states and helps to understand the rich spin excitation spectrum on the skyrmion background.

cond-mat.mes-hall↗

arXiv2009

Two-dimensional GaAs/AlGaAs superlattice structures for solar cell applications: ultimate efficiency estimation

We calculate the band structure of a two-dimensional GaAs/AlGaAs superlattice and estimate the ultimate efficiency of solar cells using this type of structure for solar energy conversion. The superlattice under consideration consists of gallium arsenide rods forming a square lattice and embedded in aluminium gallium arsenide. The ultimate efficiency is determined versus structural parameters including the filling fraction, the superlattice constant, the rod geometry and the concentration of Al in the matrix material. The calculated efficiency of the superlattice proves to exceed the efficiency of each component material in the monolithic state in a wide range of parameter values.

cond-mat.mes-hall↗