2,563 research outputs found
Non-uniform spin wave softening in 2D magnonic crystals as a tool for opening omnidirectional magnonic band gaps
By means of the plane wave method we study spin wave dynamics in
two-dimensional bi-component magnonic crystals based on a squeezed hexagonal
lattice and consist of a permalloy thin film with cobalt inclusions. We explore
the dependence of a spin wave frequency on the external magnetic field,
especially in weak fields where the mode softening takes place. For considered
structures, the mode softening proves to be highly non-uniform on both the mode
number and the wave vector. We found this effect to be responsible for the
omnidirectional band gap opening. Moreover, we show that the enhancement of the
demagnetizing field caused by the squeezing of the structure is of crucial
importance for the non-uniform mode softening. This allows us to employ this
mechanism to design magnonic gaps with different sensitivity for the tiny
change of the external field. The effects we have found should be useful in
designing and optimization of spin wave filters highly tunable by a small
external magnetic field.Comment: Final versio
Angular Dependent Magnetization Dynamics of Kagome Artificial Spin Ice Incorporating Topological Defects
We report angular-dependent spin-wave spectroscopy on kagome artificial spin
ice made of large arrays of interconnected Ni80Fe20 nanobars. Spectra taken in
saturated and disordered states exhibit a series of resonances with
characteristic in-plane angular dependencies. Micromagnetic simulations allow
us to interpret characteristic resonances of a two-step magnetization reversal
of the nanomagnets. The dynamic properties are consistent with topological
defects that are provoked via a magnetic field applied at specific angles.
Simulations that we performed on previously investigated kagome artificial spin
ice consisting of isolated nanobars show characteristic discrepancies in the
spin wave modes which we explain by the absence of vertices.Comment: 14 pages and 5 figure
Optimization of the extraordinary magnetoresistance in semiconductor-metal hybrid structures for magnetic-field sensor applications
Semiconductor-metal hybrid structures can exhibit a very large geometrical
magnetoresistance effect, the so-called extraordinary magnetoresistance (EMR)
effect. In this paper, we analyze this effect by means of a model based on the
finite element method and compare our results with experimental data. In
particular, we investigate the important effect of the contact resistance
between the semiconductor and the metal on the EMR effect. Introducing
a realistic in our model we find
that at room temperature this reduces the EMR by 30% if compared to an analysis
where is not considered.Comment: 4 pages; manuscript for MSS11 conference 2003, Nara, Japa
Angular Dependent Magnetization Dynamics with Mirror-symmetric Excitations in Artificial Quasicrystalline Nanomagnet Lattices
We report angle-dependent spin-wave spectroscopy on aperiodic
quasicrystalline magnetic lattices, i.e., Ammann, Penrose P2 and P3 lattices
made of large arrays of interconnected NiFe nanobars. Spin-wave
spectra obtained in the nearly saturated state contain distinct sets of
resonances with characteristic angular dependencies for applied in-plane
magnetic fields. Micromagnetic simulations allow us to attribute detected
resonances to mode profiles with specific mirror symmetries. Spectra in the
reversal regime show systematic emergence and disappearance of spin wave modes
indicating reprogrammable magnonic characteristics
Linearly polarized GHz magnetization dynamics of spin helix modes in the ferrimagnetic insulator CuOSeO
Linear dichroism -- the polarization dependent absorption of electromagnetic
waves -- is routinely exploited in applications as diverse as structure
determination of DNA or polarization filters in optical technologies. Here
filamentary absorbers with a large length-to-width ratio are a prerequisite.
For magnetization dynamics in the few GHz frequency regime strictly linear
dichroism was not observed for more than eight decades. Here, we show that the
bulk chiral magnet CuOSeO exhibits linearly polarized magnetization
dynamics at an unexpectedly small frequency of about 2 GHz. Unlike optical
filters that are assembled from filamentary absorbers, the magnet provides
linear polarization as a bulk material for an extremely wide range of
length-to-width ratios. In addition, the polarization plane of a given mode can
be switched by 90 via a tiny variation in width. Our findings shed a
new light on magnetization dynamics in that ferrimagnetic ordering combined
with anisotropic exchange interaction offers strictly linear polarization and
cross-polarized modes for a broad spectrum of sample shapes. The discovery
allows for novel design rules and optimization of microwave-to-magnon
transduction in emerging microwave technologies.Comment: 20 pages, 4 figure
Tuning of the Gap in a Laughlin-Bychkov-Rashba Incompressible Liquid
We report on our investigation of the influence of Bychkov-Rashba spin-orbit
interaction (SOI) on the incompressible Laughlin state. We find that
experimentally obtainable values of the spin-orbit coupling strength can induce
as much as a 25% increase in the quasiparticle-quasihole gap Eg at low magnetic
fields in InAs, thereby increasing the stability of the liquid state. The
SOI-modulated enhancement of Eg is also significant for filling factors 1/5 and
1/7, where the FQH state is usually weak. This raises the intriguing
possibility of tuning, via the SO coupling strength, the liquid to solid
transition to much lower densities.Comment: 4 pages, 3 figure
Spin-Orbit Coupling and Tunneling Current in a Parabolic Quantum Dot
We propose a novel approach to explore the properties of a quantum dot in the
presence of the spin-orbit interaction and in a tilted magnetic field. The
spin-orbit coupling within the quantum dot manifest itself as anti-crossing of
the energy levels when the tilt angle is varied. The anti-crossing gap has a
non-monotonic dependence on the magnitude of the magnetic field and exhibits a
peak at some finite values of the magnetic field. From the dependence of the
tunneling current through the quantum dot on the bias voltage and the tilt
angle, the anti-crossing gap and most importantly the spin-orbit strength can
be uniquely determined
Curved One-Dimensional Wire as a Spin Rotator
We propose a semiconductor structure that can rotate the electron spin
without using ferromagnetic contacts, tunneling barriers, external radiation
etc. The structure consists of a strongly curved one-dimensional ballistic wire
with intrinsic spin-orbit interactions of Rashba type. Our calculations and
analytical formulae show that the proposed device can redistribute the current
densities between the two spin-split modes without backscattering and, thus,
serve as a reflectionless and high-speed spin switcher. Using parameters
relevant for InAs we investigate the projection of current density spin
polarization on the spin-quantization axis as a function of the Rashba
constant, external magnetic field, and radius of the wire's curvature.Comment: 10 pages, 6 figures; replaced with considerably extended versio
Low spin wave damping in the insulating chiral magnet CuOSeO
Chiral magnets with topologically nontrivial spin order such as Skyrmions
have generated enormous interest in both fundamental and applied sciences. We
report broadband microwave spectroscopy performed on the insulating chiral
ferrimagnet CuOSeO. For the damping of magnetization dynamics we
find a remarkably small Gilbert damping parameter of about at
5 K. This value is only a factor of 4 larger than the one reported for the best
insulating ferrimagnet yttrium iron garnet. We detect a series of sharp
resonances and attribute them to confined spin waves in the mm-sized samples.
Considering the small damping, insulating chiral magnets turn out to be
promising candidates when exploring non-collinear spin structures for high
frequency applications.Comment: 5 pages, 5 figures, and supplementary materia
Observation of vortex-nucleated magnetization reversal in individual ferromagnetic nanotubes
The reversal of a uniform axial magnetization in a ferromagnetic nanotube
(FNT) has been predicted to nucleate and propagate through vortex domains
forming at the ends. In dynamic cantilever magnetometry measurements of
individual FNTs, we identify the entry of these vortices as a function of
applied magnetic field and show that they mark the nucleation of magnetization
reversal. We find that the entry field depends sensitively on the angle between
the end surface of the FNT and the applied field. Micromagnetic simulations
substantiate the experimental results and highlight the importance of the ends
in determining the reversal process. The control over end vortex formation
enabled by our findings is promising for the production of FNTs with tailored
reversal properties.Comment: 20 pages, 13 figure
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