13 research outputs found
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.Comment: 11 pages, 7 figure
Shaping magnetization dynamics in a planar square dot by adjusting its surface anisotropy
A planar square dot is one of the simplest structures confined to three
dimensions. Despite its geometrical simplicity, the description of the spin
wave modes in this structure is not trivial due to the competition of dipolar
and exchange interactions. An additional factor that makes this description
challenging are the boundary conditions depend both on non-local dipolar
interactions and local surface parameters such as surface anisotropy. In the
presented work, we showed how the surface anisotropy applied at the lateral
faces of the dot can tune the frequency of fundamental mode in the planar CoFeB
dot, magnetized in an out-of-plane direction. Moreover, we analyzed the spin
wave profile of the fundamental mode and the corresponding dynamic stray field.
We showed that the asymmetric application of surface anisotropy produces an
asymmetric profile of dynamic stray field for square dot and can be used to
tailor inter-dot coupling. The calculations were performed with the use of the
finite-element method.Comment: 4 pages, 4 figure
The correspondence between topological properties and existence conditions for interface modes in planar one-dimensional magnonic crystals
We present the concept of Zak phase for spin waves in planar magnonic
crystals and discuss the conditions for the existence of interface modes
localized on the boundary between two magnonic crystals with centrosymmetric
unit cells. Using the symmetry criterion and the calculated logarithmic
derivative of the Bloch function we study the interface modes to demonstrate
the bulk-edge correspondence. Our theoretical results are verified numerically
for structures in the exchange and exchange-dipolar regimes and extended to the
case in which one of the magnonic crystals has an arbitrary unit cell.
Moreover, we show that by shifting the unit cell the interface modes can be
caused to traverse the bandgap edges
Compact localised states in magnonic Lieb lattices
Lieb lattice is one of the simplest bipartite lattices where compact
localized states (CLS) are observed. This type of localisation is induced by
the peculiar topology of the unit cell, where the modes are localized only on
one sublattice due to the destructive interference of partial waves. The CLS
exist in the absence of defects and are associated with the flat bands in the
dispersion relation. The Lieb lattices were successfully implemented as optical
lattices or photonic crystals. This work demonstrates the possibility of
magnonic Lieb lattice realization where the flat bands and CLS can be observed
in the planar structure of sub-micron in-plane sizes. Using forward volume
configuration, we investigated numerically (using the finite element method)
the Ga-dopped YIG layer with cylindrical inclusions (without Ga content)
arranged in a Lieb lattice of the period 250 nm. We tailored the structure to
observe, for the few lowest magnonic bands, the oscillatory and evanescent spin
waves in inclusions and matrix, respectively. Such a design reproduces the Lieb
lattice of nodes (inclusions) coupled to each other by the matrix with the CLS
in flat bands
Unidirectional spin wave emission by travelling pair of magnetic field profiles
We demonstrate that the spin wave Cherenkov effect can be used to design the
unidirectional spin wave emitter with tunable frequency and switchable
direction of emission. In our numerical studies, we propose to use a pair of
traveling profiles of the magnetic field which generate the spin waves, for
sufficiently large velocity of their motion. In the considered system, the spin
waves of shorter (longer) wavelengths are induced at the front (back) of the
moving profiles and interfere constructively or destructively, depending on the
velocity of the profiles. Moreover, we showed that the spin waves can be
confined between the pair of traveling profiles of the magnetic field. This
work opens the perspectives for the experimental studies in hybrid
magnonic-superconducting systems where the magnetic vortices in a
superconductor can be used as moving sources of the magnetic field driving the
spin waves in the ferromagnetic subsystem.Comment: 4 pages, 3 figure
Multifunctional operation of the double-layer ferromagnetic structure coupled by a rectangular nanoresonator
The use of spin waves as a signal carrier requires developing the functional elements allowing for multiplexing and demultiplexing information coded at different wavelengths. For this purpose, we propose a system of thin ferromagnetic layers dynamically coupled by a rectangular ferromagnetic resonator. We show that a single and double, clockwise and counter-clockwise, circulating modes of the resonator offer a wide possibility of control of propagating waves. Particularly, at frequency related to the double-clockwise circulating spin-wave mode of the resonator, the spin wave excited in one layer is transferred to the second one where it propagates in the backward direction. Interestingly, the wave excited in the second layer propagates in the forward direction only in that layer. This demonstrates add-drop filtering, as well as circulator functionality. Thus, the proposed system can become an important part of future magnonic technology for signal routing.The research leading to these results has received funding from the Polish National Science Centre, project no. UMO 2018/30/Q/ST3/00416