933 research outputs found
Monte Carlo study of magnetic nanoparticles adsorbed on halloysite nanotubes
We study properties of magnetic nanoparticles adsorbed on the halloysite
surface. For that a distinct magnetic Hamiltonian with random distribution of
spins on a cylindrical surface was solved by using a nonequilibrium Monte Carlo
method. The parameters for our simulations: anisotropy constant, nanoparticle
size distribution, saturated magnetization and geometrical parameters of the
halloysite template were taken from recent experiments. We calculate the
hysteresis loops and temperature dependence of the zero field cooling (ZFC)
susceptibility, which maximum determines the blocking temperature. It is shown
that the dipole-dipole interaction between nanoparticles moderately increases
the blocking temperature and weakly increases the coercive force. The obtained
hysteresis loops (e.g., the value of the coercive force) for Ni nanoparticles
are in reasonable agreement with the experimental data. We also discuss the
sensitivity of the hysteresis loops and ZFC susceptibilities to the change of
anisotropy and dipole-dipole interaction, as well as the 3d-shell occupation of
the metallic nanoparticles; in particular we predict larger coercive force for
Fe, than for Ni nanoparticles.Comment: 10 pages, 12 figure
Bimeron nanoconfined design
We report on the stabilization of the topological bimeron excitations in
confined geometries. The Monte Carlo simulations for a ferromagnet with a
strong Dzyaloshinskii-Moriya interaction revealed the formation of a mixed
skyrmion-bimeron phase. The vacancy grid created in the spin lattice
drastically changes the picture of the topological excitations and allows one
to choose between the formation of a pure bimeron and skyrmion lattice. We
found that the rhombic plaquette provides a natural environment for
stabilization of the bimeron excitations. Such a rhombic geometry can protect
the topological state even in the absence of the magnetic field.Comment: 5 pages, 7 figure
Profile approach for recognition of three-dimensional magnetic structures
We propose an approach for low-dimensional visualisation and classification
of complex topological magnetic structures formed in magnetic materials. Within
the approach one converts a three-dimensional magnetic configuration to a
vector containing the only components of the spins that are parallel to the z
axis. The next crucial step is to sort the vector elements in ascending or
descending order. Having visualized profiles of the sorted spin vectors one can
distinguish configurations belonging to different phases even with the same
total magnetization. For instance, spin spiral and paramagnetic states with
zero total magnetic moment can be easily identified. Being combined with a
simplest neural network our profile approach provides a very accurate phase
classification for three-dimensional magnets characterized by complex
multispiral states even in the critical areas close to phases transitions. By
the example of the skyrmionic configurations we show that profile approach can
be used to separate the states belonging to the same phase
Variational optimization of tensor-network states with the honeycomb-lattice corner transfer matrix
We develop a method of variational optimization of the infinite projected
entangled pair states on the honeycomb lattice. The method is based on the
automatic differentiation of the honeycomb lattice corner transfer matrix
renormalization group. We apply the approach to the antiferromagnetic
Heisenberg spin-1/2 model on the honeycomb lattice. The developed formalism
gives quantitatively accurate results for the main physical observables and has
a necessary potential for further extensions
Supervised learning magnetic skyrmion phases
We propose and apply simple machine learning approaches for recognition and
classification of complex non-collinear magnetic structures in two-dimensional
materials. The first approach is based on the implementation of the
single-hidden-layer neural network that only relies on the z projections of the
spins. In this setup one needs a limited set of magnetic configurations to
distinguish ferromag- netic, skyrmion and spin spiral phases, as well as their
different combinations in transitional areas of the phase diagram. The network
trained on the configurations for square-lattice Heisenberg model with
Dzyaloshinskii-Moriya interaction can classify the magnetic structures obtained
from Monte Carlo calculations for triangular lattice and vice versa. The second
approach we apply, a minimum distance method performs a fast and cheap
classification in cases when a particular configuration is to be assigned to
only one magnetic phase. The methods we propose are also easy to use for
analysis of the numerous experimental data collected with spin-polarized
scanning tunneling microscopy and Lorentz transmission electron microscopy
experiments.Comment: 9 pages, 14 figures. Accepted for publication in Physical Review
About a contactless transmission of 10 keV electrons through tapering microchannels
The possibility of increasing the current density of a beam of fast electrons passes through glass cone-shaped channels was demonstrated in. But the fraction of the electrons that passed through the conical channels without loss of the initial energy was not cleared up. Measurements of X-ray spectra generated by transmitted electrons in copper target mounted in vicinity of capillary output were performed for a detailed study of the contactless passage of 10 keV electrons through conical capillarie
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