arXiv subjects

Yuri Gaididei

Publications and source records attributed to Yuri Gaididei.

At least 37 records · Page 2Linked to original sources

arXiv2015

Curvature induced domain wall pinning

It is shown that a local bend of a nanowire is a source of pinning potential for a transversal head-to-head (tail-to-tail) domain wall. Eigenfrequency of the domain wall free oscillations at the pinning potential and the effective friction are determined as functions of the curvature and domain wall width. The pinning potential originates from the effective curvature induced Dzyaloshinsky-like term in the exchange energy. The theoretical results are verified by means of micromagnetic simulations for the case of parabolic shape of the wire bend.

cond-mat.mes-hall↗

arXiv2015

Resonantly exited precession motion of three-dimensional vortex core in magnetic nanospheres

We found resonantly excited precession motions of a three-dimensional vortex core in soft magnetic nanospheres and controllable precession frequency with the sphere diameter 2R, as studied by micromagnetic numerical and analytical calculations. The precession angular frequency for an applied static field $H_{DC}$ is given as $ω_{MV}= γ_{eff} H_{DC}$, where $γ_{eff} = γ $ is the effective gyromagnetic ratio in collective vortex dynamics, with the gyromagnetic ratio $γ$ and the average magnetization component $ $ of the ground-state vortex in the core direction. Fitting to the micromagnetic simulation data for $ $ yields a simple explicit form of $ = (73.6 \pm 3.4)(l_{ex}/2R)^{2.20 \pm 0.14}$, where $l_{ex}$ is the exchange length of a given material. This dynamic behavior might serve as a foundation for potential bio-applications of size-specific resonant excitation of magnetic vortex-state nanoparticles, for example, magnetic particle resonance imaging.

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arXiv2015

Magnetization patterning induced by electrical spin-polarized current in nanostripes

The combined action of a transverse spin-polarized current and the current-induced Ørsted field on long ferromagnetic nanostripes is studied numerically and analytically. The magnetization behavior is analyzed for stripes with various widths and for all range of the applied current density. It is established that Ørsted field does not destroy periodical magnetization structures induced by the spin-torque, e.g. vortex-antivortex crystal and cross-tie domain walls. However, the action of the Ørsted field disables the saturation state for the strong currents: a stationary state with a single longitudinal domain wall appears instead. Shape of this wall remains constant with the current increasing. The latter phenomenon is studied both numerically and analytically.

cond-mat.mes-hall↗

arXiv2015

Curvature effects in statics and dynamics of low dimensional magnets

We develop an approach to treat magnetic energy of a ferromagnet for arbitrary curved wires and shells on the assumption that the anisotropy contribution much exceeds the dipolar and other weak interactions. We show that the curvature induces two effective magnetic interactions: effective magnetic anisotropy and effective Dzyaloshinskii-like interaction. We derive an equation of magnetisation dynamics and propose a general static solution for the limit case of strong anisotropy. To illustrate our approach we consider the magnetisation structure in a ring wire and a cone surface: ground states in both systems essentially depend on the curvature excluding strictly tangential solutions even in the case of strong anisotropy. We derive also the spectrum of spin waves in such systems.

cond-mat.mes-hall↗

arXiv2015

Vortex Polarity Switching in Magnets with Surface Anisotropy

Vortex core reversal in magnetic particle is essentially influenced by a surface anisotropy. Under the action of a perpendicular static magnetic field the vortex core undergoes a shape deformationof pillow- or barrel-shaped type, depending on the type of the surface anisotropy. This deformation plays a key point in the switching mechanism: We predict that the vortex polarity switching is accompanied (i) by a linear singularity in case of Heisenberg magnet with bulk anisotropy only and (ii) by a point singularities in case of surface anisotropy or exchange anisotropy. We study in details the switching process using spin-lattice simulations and propose a simple analytical description using a wired core model, which provides an adequate description of the Bloch point statics, its dynamics and the Bloch point mediated switching process. Our analytical predictions are confirmed by spin-lattice simulations for Heisenberg magnet and micromagnetic simulations for nanomagnet with account of a dipolar interaction.

cond-mat.str-el↗

arXiv2014

Curvature effects in vortex chirality switching

A simple mechanism of controllable switching of magnetic vortex chirality is proposed. We consider curvilinear magnetic nanoshells of spherical geometry whose ground state is a vortex magnetization distribution. Chirality of this magnetic vortex can be switched in controllable way by applying a Gaussian pulse of spatially uniform magnetic field along the symmetry axis of the shell. The chirality switching process is explored in detail numerically for various parameters of magnetic pulse: the corresponding switching diagram is build. The role of the curvature is ascertained by studying the switching diagram evolution under the continuous transition from hemispherical shell to the disk shaped sample with the volume and thickness kept constant.

cond-mat.mes-hall↗

arXiv2014

Magnetochiral symmetry breaking in a Möbius ring

We show that the interaction of the magnetic subsystem of a curved magnet with the magnet curvature results in coupling of a topologically nontrivial magnetization pattern and topology of the object. The mechanism of this coupling is explored and illustrated by an example of ferromagnetic Möbius ring, where a topologically induced domain wall appears as a ground state in case of strong easy-normal anisotropy. For the Möbius geometry the curvilinear form of the exchange interaction produces an additional effective Dzyaloshinskii-like term which leads to the coupling of the magnetochirality of the domain wall and chirality of the Möbius ring. Two types of domain walls are found, transversal and longitudinal, which are oriented across and along the Möbius ring, respectively. In both cases the effect of magnetochirality symmetry breaking is established. The dependence of the ground state of the Möbius ring on its geometrical parameters and on the value of the easy-normal anisotropy is explored numerically.

cond-mat.mes-hall↗

arXiv2014

Curvature induced chirality symmetry breaking in vortex core switching phenomena

The interplay between magnetic vortex polarity, chirality and the curvature of the underlying surface results in a dependence of the vortex polarity switching efficiency on the vortex chirality. The switching is studied numerically by applying a short Gauss pulse of the external magnetic field to a spherical cap within its cut plane. The minimum field intensity required for the switching essentially depends on the vortex chirality and it does not depend on the initial vortex polarity. This effect decreases with the curvature radius increasing and it vanishes in the planar limit.

cond-mat.mes-hall↗

arXiv2013

Curvature effects in statics and dynamics of a thin magnetic shell

Equations of the magnetization dynamics are derived for an arbitrary curved 2D surface. General static solutions are obtained in the limit of a strong anisotropy of both signs (easy-surface and easy-normal cases). It is shown that the effect of the curvature can be treated as appearance of an effective magnetic field which is aligned along the surface normal for the case of easy-surface anisotropy and it is tangential to the surface for the case of easy-normal anisotropy. In general, the existence of such a field denies the solutions strictly tangential as well as strictly normal to the surface. As an example we consider static equilibrium solutions and linear dynamics for a cone surface magnetization.

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arXiv2013

Effects of Surface Anisotropy on Magnetic Vortex Core

The vortex core shape in the three dimensional Heisenberg magnet is essentially influenced by a surface anisotropy. We predict that depending of the surface anisotropy type there appears barrel- or pillow-shaped deformation of the vortex core along the magnet thickness. Our theoretical study is well confirmed by spin-lattice simulations.

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arXiv2013

Equilibrium states of soft magnetic hemispherical shell

The ground state of hemispherical permalloy magnetic shell is studied. There exist two magnetic phases: the onion state and the vortex one. The phase diagram is systematically analyzed in a wide range of geometrical parameters. Possible transitions between different phases are analyzed using the combination of analytical calculations and micromagnetic simulations.

cond-mat.mes-hall↗

arXiv2013

Periodic magnetic structures generated by spin-polarized currents in nanostripes

The influence of a spin-polarized current on long ferromagnetic nanostripes is studied numerically. The current flows perpendicularly to the stripe. The study is based on the Landau-Lifshitz phenomenological equation with the Slonczewski-Berger spin-torque term. The magnetization behavior is analyzed for all range of the applied currents, up to the saturation. It is shown that the saturation current is a nonmonotonic function of the stripe width. For a stripe width increasing it approaches the saturation value for an infinite film. A number of stable periodic magnetization structures are observed below the saturation. Type of the periodical structure depends on the stripe width. Besides the one-dimensional domain structure, typical for narrow wires, and the two-dimensional vortex-antivortex lattice, typical for wide films, a number of intermediate structures are observed, e.g. cross-tie and diamond state. For narrow stripes an analytical analysis is provided.

cond-mat.mes-hall↗

arXiv2013

Regular and chaotic vortex core reversal by a resonant perpendicular magnetic field

Under the action of an alternating perpendicular magnetic field the polarity of the vortex state nanodisk can be efficiently switched. We predict the regular and chaotic dynamics of the vortex polarity and propose simple analytical description in terms of a reduced vortex core model. Conditions for the controllable polarity switching are analyzed.

cond-mat.mes-hall↗

arXiv2013

Periodic magnetization structures generated by transverse spin-current in magnetic nanowires

Magnetization behavior of long nanowires with square cross-section under influence of strong perpendicular spin-polarized current is studied theoretically. The study is based on Landau-Lifshitz-Slonczewski phenomenology. In the no current case the wire is magnetized uniformly along its axis. For small currents the wire magnetization remains uniform but it inclines with respect to the wire axis within the plane perpendicular to the current direction. With the current increasing the inclination angle increases up to the maximum value $π/4$. Further current increase leads either to saturation or to stable periodic multidomain structure depending on the wire thickness. For thick wires a hysteresis is observed in the saturation process under the action of current. All critical parameters of the current induced magnetization behavior are determined theoretically. The study is carried out both analytically and using micromagnetic simulations.

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arXiv2012

Mechanism of Fast Axially--Symmetric Reversal of Magnetic Vortex Core

The magnetic vortex core in a nanodot can be switched by an alternating transversal magnetic field. We propose a simple collective coordinate model which describes comprehensive vortex core dynamics, including resonant behavior, weakly nonlinear regimes, and reversal dynamics. A chaotic dynamics of the vortex polarity is predicted. All analytical results were confirmed by micromagnetic simulations.

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arXiv2012

Magnetic vortex-antivortex crystals generated by spin-polarized current

We study vortex pattern formation in thin ferromagnetic films under the action of strong spin-polarized currents. Considering the currents which are polarized along the normal of the film plane, we determine the critical current above which the film goes to a saturated state with all magnetic moments being perpendicular to the film plane. We show that stable square vortex-antivortex superlattices (\emph{vortex crystals}) appears slightly below the critical current. The melting of the vortex crystal occurs with current further decreasing. A mechanism of current-induced periodic vortex-antivortex lattice formation is proposed. Micromagnetic simulations confirm our analytical results with a high accuracy.

cond-mat.str-el↗

arXiv2012

Bloch Point Structure in a Magnetic Nanosphere

The micromagnetic singularity, the so-called Bloch point, can form a metastable state in the nanosphere. We classify possible types of Bloch points and derive analytically the shape of magnetization distribution inside different Bloch point. We show that external gradient field can stabilize the Bloch point: the shape of the Bloch point becomes radial-dependent one and compute the magnetization structure of the nanosphere, which is in a good agrement with performed spin-lattice simulations.

cond-mat.mes-hall↗

arXiv2012

Out-of-surface vortices in spherical shells

The interplay of topological defects with curvature is studied for out-of-surface magnetic vortices in thin spherical nanoshells. In the case of easy-surface Heisenberg magnet it is shown that the curvature of the underlying surface leads to a coupling between the localized out-of-surface component of the vortex with its delocalized in-surface structure, i.e. polarity-chirality coupling.

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