17 research outputs found
Spin wave vortex from the scattering on Bloch point solitons
The interaction of a spin wave with a stationary Bloch point is studied. The
topological non-trivial structure of the Bloch point manifests in the
propagation of spin waves endowing them with a gauge potential that resembles
the one associated with the interaction of a magnetic monopole and an electron.
By pursuing this analogy, we are led to the conclusion that the scattering of
spin waves and Bloch points is accompanied by the creation of a magnon vortex.
Interference between such a vortex and a plane wave leads to dislocations in
the interference pattern that can be measurable by means of magnon holography
On geometry-dependent vortex stability and topological spin excitations on curved surfaces with cylindrical symmetry
We study the Heisenberg Model on cylindrically symmetric curved surfaces. Two
kinds of excitations are considered. The first is given by the isotropic
regime, yielding the sine-Gordon equation and -solitons are predicted. The
second one is given by the XY model, leading to a vortex turning around the
surface. Helical states are also considered, however, topological arguments can
not be used to ensure its stability. The energy and the anisotropy parameter
which stabilizes the vortex state are explicitly calculated for two surfaces:
catenoid and hyperboloid. The results show that the anisotropy and the vortex
energy depends on the underlying geometry.Comment: 10 pages, 2 figures, Accepted for publication in Phys. Lett A (2013
Coupling between magnetic field and curvature in Heisenberg spins on surfaces with rotational symmetry
We study the nonlinear -model in an external magnetic field applied
on curved surfaces with rotational symmetry. The Euler-Lagrange equations
derived from the Hamiltonian yield the double sine-Gordon equation (DSG)
provided the magnetic field is tuned with the curvature of the surface. A
skyrmion appears like a solution for this model and surface deformations
are predicted at the sector where the spins point in the opposite direction to
the magnetic field. We also study some specific examples by applying the model
on three rotationally symmetric surfaces: the cylinder, the catenoid and the
hyperboloid. The coupling between a magnetic field and the curvature of the
substract is an interesting result and we believe that this issue may be
relevant to be applied in condensed matter systems, e.g., superconductors,
nematic liquid crystals, graphene and topological insulators.Comment: To be published in Physics Letters
Tuning domain wall dynamics by shaping nanowires cross-sections.
The understanding of the domain wall (DW) dynamics along magnetic nanowires is crucial for spintronic applications. In this work, we perform a detailed analysis of the transverse DW motion along nanowires with polygonal cross-sections. If the DW displaces under a magnetic field above the Walker limit, the oscillatory motion of the DW is observed. The amplitude, the frequency of oscillations, and the DW velocity depend on the number of sides of the nanowire cross-section, being the DW velocity in a wire with a triangular cross-section one order of magnitude larger than that in a circular nanowire. The decrease in the nanowire cross-section area yields a DW behavior similar to the one presented in a cylindrical nanowire, which is explained using an analytical model based on the general kinetic momentum theorem. Micromagnetic simulations reveal that the oscillatory behavior of the DW comes from energy changes due to deformations of the DW shape during the rotation around the nanowire
Magnetization ground state and reversal modes of magnetic nanotori
In this work, and by means of micromagnetic simulations, we study the magnetic properties of toroidal nanomagnets. The magnetization ground state for different values of the aspect ratio between the toroidal and polar radii of the nanotorus has been obtained. Besides, we have shown that the vortex and the in-plane single domain states can appear as ground states for different ranges of the aspect ratio, while a single domain state with an out-of-plane magnetization is not observed. The hysteresis curves are also obtained, evidencing the existence of two reversal modes depending on the geometry: a vortex mode and a coherent rotation. A comparison between toroidal and cylindrical nanoparticles has been performed evidencing that nanotori can accommodate a vortex as the ground state for smaller volume than cylindrical nanorings. Published by AIP Publishing.FONDECYT, Financiamiento Basal FB para Centros Cientificos y Tecnologicos de Excelencia, CNP
Topological magnetic solitons on a paraboloidal shell
We study the influence of curvature on the exchange energy of skyrmions and vortices on a paraboloidal surface. It is shown that such structures appear as excitations of the Heisenberg model, presenting topological stability, unlike what happens on other simply-connected geometries such as pseudospheres. We also show that the skyrmion width depends on the geometrical parameters of the paraboloid. The presence of a magnetic field leads to the appearance of 2π-skyrmions, introducing a new characteristic length into the system. Regarding vortices, the geometrical parameters of the paraboloid play an important role in the exchange energy of this excitation