409 research outputs found
Skyrmions and antiskyrmions in monoaxial chiral magnets
We show that competition between local interactions in monoaxial chiral
magnets provides the stability of two-dimensional (2D) solitons with identical
energies but opposite topological charges. These skyrmions and antiskyrmions
represent metastable states in a wide range of parameters above the transition
into the saturated ferromagnetic phase. The symmetry of the underlying
micromagnetic functional gives rise to soliton zero modes allowing efficient
control of their translational movement by the frequency of the circulating
external magnetic field. We also discuss the role of demagnetizing fields in
the energy balance between skyrmion and antiskyrmion and in their stability.Comment: 5 pages, 3 figure
Turning chiral skyrmion inside out
The stability of two-dimensional chiral skyrmions in a tilted magnetic field
is studied. It is shown that by changing the direction of the field and its
magnitude, one can continuously transform chiral skyrmion into a skyrmion with
opposite polarity and vorticity. This turned inside out skyrmion can be
considered as an antiparticle for ordinary axisymmetric skyrmion. For any tilt
angle of the magnetic field, there is a range of its absolute values where two
types of skyrmions may coexist. In a tilted field, the potentials for
inter-skyrmion interactions are characterized by the presence of local minima
suggesting attractive interaction between the particles. The potentials of
inter-particle interactions also have so-called fusion channels allowing either
annihilation of two particles or the emergence of a new particle. The presented
results are general for a wide class of magnetic crystals with both easy-plane
and easy-axis anisotropy
Homotopy transitions and 3D magnetic solitons
This work provides a concept for three-dimensional magnetic solitons based on
mapping the homotopy path between various two-dimensional solutions onto the
third spatial axis. The representative examples of statically stable
configurations of that type in the model of an isotropic chiral magnet are
provided. Various static and dynamic properties of such three-dimensional
magnetic solitons are discussed in detail.Comment: 9 pages, 6 figure
Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states
Magnetic chiral skyrmions are vortex like spin structures that appear as
stable or meta-stable states in magnetic materials due to the interplay between
the symmetric and antisymmetric exchange interactions, applied magnetic field
and/or uniaxial anisotropy. Their small size and internal stability make them
prospective objects for data storage but for this, the controlled switching
between skyrmion states of opposite polarity and topological charge is
essential. Here we present a study of magnetic skyrmion switching by an applied
magnetic field pulse based on a discrete model of classical spins and atomistic
spin dynamics. We found a finite range of coupling parameters corresponding to
the coexistence of two degenerate isolated skyrmions characterized by mutually
inverted spin structures with opposite polarity and topological charge. We
demonstrate how for a wide range of material parameters a short inclined
magnetic field pulse can initiate the reliable switching between these states
at GHz rates. Detailed analysis of the switching mechanism revealed the complex
path of the system accompanied with the excitation of a chiral-achiral meron
pair and the formation of an achiral skyrmion
Tailed skyrmions -- an obscure branch of magnetic solitons
We report tailed skyrmions -- a new class of stable soliton solutions of the
2D chiral magnet model. Tailed skyrmions have elongated shapes and emerge in a
narrow range of fields near the transition between the spin spirals and the
saturated state. We analyze the stability range of these solutions in terms of
external magnetic field and magnetocrystalline anisotropy. Minimum energy paths
and the homotopies (continuous transitions) between tailed skyrmions of the
same topological charge have been calculated using the geodesic nudged elastic
bands method. The discovery of tailed skyrmions extends the diversity of
already-known solutions illustrated by complex morphology solitons, such as
tailed skyrmion bags with and without chiral kinks.Comment: 7 pages, 6 figure
Antiskyrmions stabilized at interfaces by anisotropic Dzyaloshinskii-Moriya interaction
Chiral magnets are an emerging class of topological matter harbouring
localized and topologically protected vortex-like magnetic textures called
skyrmions, which are currently under intense scrutiny as a new entity for
information storage and processing. Here, on the level of micromagnetics we
rigorously show that chiral magnets cannot only host skyrmions but also
antiskyrmions as least-energy configurations over all non-trivial homotopy
classes. We derive practical criteria for their occurrence and coexistence with
skyrmions that can be fulfilled by (110)-oriented interfaces in dependence on
the electronic structure. Relating the electronic structure to an atomistic
spin-lattice model by means of density-functional calculations and minimizing
the energy on a mesoscopic scale applying spin-relaxation methods, we propose a
double layer of Fe grown on a W(110) substrate as a practical example. We
conjecture that ultrathin magnetic films grown on semiconductor or heavy metal
substrates with symmetry are prototype classes of materials hosting
magnetic antiskyrmions.Comment: 20 pages (11 pages + 9 pages supplementary material
Thermal generation of droplet soliton in chiral magnet
Controlled creation of localized magnetic textures beyond conventional π-skyrmions is an important problem in the field of magnetism. Here, by means of spin dynamics simulations, Monte Carlo simulations, and harmonic transition state theory we demonstrate that an elementary chiral magnetic soliton with zero topological charge—the chiral droplet—can be created by thermal fluctuations in the presence of the tilted magnetic field. The proposed protocol relies on an unusual kinetics combining the effects of the entropic stabilization and low-energy barrier for the nucleation of a topologically trivial state. Following this protocol by varying temperature and the tilt of the external magnetic field, one can selectively generate chiral droplets or π-skyrmions in a single system. The coexistence of two distinct magnetic solitons establishes a basis for a rich magnetization dynamics and opens up the possibility for the construction of more complex magnetic textures such as skyrmion bags and skyrmions with chiral kinks.Deutsche Forschungsgemeinschaft (DFG) through SPP 2137 "Skyrmionics" Grant No. KI 2078/1-1, the Russian Science Foundation (Grant No. 19-72-10138), the Icelandic Research Fund (Grant Nos. 184949 and 217750), the University of Iceland Research Fund
(Grant No. 15673), and the Swedish Research Council (Grant No. 2020-05110)Peer Reviewe
Thermal generation of droplet soliton in chiral magnet
Controlled creation of localized magnetic textures beyond conventional π-skyrmions is an important problem in the field of magnetism. Here, by means of spin dynamics simulations, Monte Carlo simulations, and harmonic transition state theory we demonstrate that an elementary chiral magnetic soliton with zero topological charge—the chiral droplet—can be created by thermal fluctuations in the presence of the tilted magnetic field. The proposed protocol relies on an unusual kinetics combining the effects of the entropic stabilization and low-energy barrier for the nucleation of a topologically trivial state. Following this protocol by varying temperature and the tilt of the external magnetic field, one can selectively generate chiral droplets or π-skyrmions in a single system. The coexistence of two distinct magnetic solitons establishes a basis for a rich magnetization dynamics and opens up the possibility for the construction of more complex magnetic textures such as skyrmion bags and skyrmions with chiral kinks.Deutsche Forschungsgemeinschaft (DFG) through SPP 2137 "Skyrmionics" Grant No. KI 2078/1-1, the Russian Science Foundation (Grant No. 19-72-10138), the Icelandic Research Fund (Grant Nos. 184949 and 217750), the University of Iceland Research Fund
(Grant No. 15673), and the Swedish Research Council (Grant No. 2020-05110)Peer Reviewe
Influence of Adding Ammonium Bifluoride when Leaching Monazite Using Sulphur Acid
The following shows the results of the leaching of monazite concentrate with sulfuric acid in the presence of ammonium bifluoride. It was established that the addition of ammonium bifluoride increases the degree of the leaching monazite concentrate and allows the separation of phosphorous from a mixture of rare earth and radioactive elements
Magnetic skyrmions, chiral kinks, and holomorphic functions
We present a novel approach to understanding the extraordinary diversity of magnetic skyrmion solutions. Our approach combines an original classification scheme with efficient analytical and numerical methods. We introduce the concept of chiral kinks to account for regions of disfavored chirality in spin textures, and classify two-dimensional magnetic skyrmions in terms of closed domain walls carrying such chiral kinks. In particular, we show that the topological charge of magnetic skyrmions can be expressed in terms of the constituent closed domain walls and chiral kinks. Guided by our classification scheme, we propose a method for creating hitherto unknown magnetic skyrmions which involves initial spin configurations formulated in terms of holomorphic functions and subsequent numerical energy minimization. We numerically study the stability of the resulting magnetic skyrmions for a range of external fields and anisotropy parameters, and provide quantitative estimates of the stability range for the whole variety of skyrmions with kinks. We show that the parameters limiting this range can be well described in terms of the relative energies of particular skyrmion solutions and isolated stripes with and without chiral kinks
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