446 research outputs found
Chiral Magnetic Skyrmions with Arbitrary Topological Charge ("skyrmionic sacks")
We show that continuous and spin-lattice models of chiral ferro- and
antiferromagnets provide the existence of an infinite number of stable soliton
solutions of any integer topological charge. A detailed description of the
morphology of new skyrmions and the corresponding energy dependencies are
provided. The considered model is general, and is expected to predict a
plethora of particle-like states which may occur in various chiral magnets
including atomic layers, e.g., PdFe/Ir(111), rhombohedral GaVS
semiconductor, B20-type alloys as MnFeGe, MnFeSi,
FeCoSi, CuOSeO, acentric tetragonal Heusler compounds
New type of stable particle like states in chiral magnets (Chiral bobbers)
We present a new type of a thermodynamically stable magnetic state at
interfaces and surfaces of chiral magnets. The state is a soliton solution of
micromagnetic equations localized in all three dimensions near a boundary and
contains a singularity, but nevertheless has a finite energy. Both features
combine to a quasi-particle state for which we expect unusual transport and
dynamical properties. It exhibits high thermal stability and thereby can be
considered as promising object for fundamental research and practical
applications in spintronic devices. We provide arguments that such a state can
be found in different B20-type alloys e.g. MnFeGe,
MnFeSi, FeCoSi.Comment: accepted in PR
SU(2) Skyrme Vortices
A regular method for constructing vortex-like solutions with cylindrical
symmetry to the equations of the SU(2) Skyrme chiral model is proposed. A
numerical estimate for the length density of mass is given
Magnetic hopfions in solids
Hopfions are an intriguing class of string-like solitons, named according to
a classical topological concept classifying three-dimensional direction fields.
The search of hopfions in real physical systems is going on for nearly half a
century, starting with the seminal work of Faddeev. But so far realizations in
solids are missing. Here, we present a theory that identifies magnetic
materials featuring hopfions as stable states without the assistance of
confinement or external fields. Our results are based on an advanced
micromagnetic energy functional derived from a spin-lattice Hamiltonian.
Hopfions appear as emergent particles of the classical Heisenberg model.
Magnetic hopfions represent three-dimensional particle-like objects of
nanometre-size dimensions opening the gate to a new generation of spintronic
devices in the framework of a truly three-dimensional architecture. Our
approach goes beyond the conventional phenomenological models. We derive
material-realistic parameters that serve as concrete guidance in the search of
magnetic hopfions bridging computational physics with materials science
Multiple Conclusion Rules in Logics with the Disjunction Property
We prove that for the intermediate logics with the disjunction property any
basis of admissible rules can be reduced to a basis of admissible m-rules
(multiple-conclusion rules), and every basis of admissible m-rules can be
reduced to a basis of admissible rules. These results can be generalized to a
broad class of logics including positive logic and its extensions, Johansson
logic, normal extensions of S4, n-transitive logics and intuitionistic modal
logics
Interaction of Individual Skyrmions in Nanostructured Cubic Chiral Magnet
We report the direct evidence of field-dependent character of the interaction
between individual magnetic skyrmions as well as between skyrmions and edges in
B20-type FeGe nanostripes observed by means of high resolution Lorentz
transmission electron microscopy. It is shown that above certain critical
values of external magnetic field the character of such long-range skyrmion
interactions change from attraction to repulsion. Experimentally measured
equilibrium inter-skyrmion and skrymion-edge distances as function of applied
magnetic field shows quantitative agreement with the results of micromagnetic
simulations. Important role of demagnetizing fields and internal symmetry of
three-dimensional magnetic skyrmions are discussed in details.Comment: accepted in PR
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