Vortex Polarity Switching Research Articles

Strain manipulation of vortex core in bi-component magnetic nanodisks

Magnetic vortex as one of the quintessentially non-uniform magnetic structure that can be found to commonly exist in micrometer or submicrometer sized ferromagnetic thin films. Here, we present that the vortex core can be efficiently expelled from the central region and excited into gyrotropic motion by using a voltage induced strain in bi-component magnetic nanodisks. In particular, the polarity can be deterministic switched by proper modulation the amplitude and frequency of applied voltage. The related results of micromagnetic simulations indicated that the magnetic vortex polarity is reversed through the nucleation-annihilation process of topological vortex-antivortex pairs or rotation-fusion edge soliton pairs. This voltage-controlled low-power vortex polarity switching scheme has the ability to accurately address individual magnets in dense arrays and also is compatible with integrated circuit techniques, which provides an additional route for the design of vortex-based on-chip devices.

The Effect of the Spin-Polarized Current on the Dynamics and Structural Changes of Magnetic Vortices in a Large-Diameter Three-Layer Conducting Nanocylinder

The structure and magnetization dynamics are investigated in a vortex spin-transfer nanooscillator, which is a three-layer spin-valve magnetic nanocolumn with a large diameter of 400 nm, under flowing spin-polarized current through it. The dynamic variation in the structure of vortices and their trajectory of motion are studied, using micromagnetic modeling, as a function of the value of the spin-polarized current. It is demonstrated that different modes of motion of vortices may exist: decaying oscillations of vortices, stationary oscillations of vortices, and the mode of switching polarity of one of vortices. The time for which different dynamic modes are settled is determined. The dependence of the oscillation frequency on the value of spin-polarized current is determined for the case of stationary dynamics of coupled vortices. It is shown that, at large values of current, switching of vortex polarity is only possible in a thick layer with the dynamic switching mechanism accompanied by generation of a vortex–antivortex pair. The software package for micromagnetic simulation, SpinPM, is used for numerical calculations of the dynamics of magnetic vortices.

Spin current induced dynamics and polarity switching of coupled magnetic vertices in three-layer nanopillars

Abstract We study dynamics of two magnetostatically coupled magnetic vortices excited by spin-polarized electrical current in a nanopillar consisting of permalloy magnetic layers with different thickness separated by a nonmagnetic spacer. We demonstrate three dynamical regimes of the vortices bound motion: damped oscillations, stationary oscillations and a regime of the polarity switching of one of the vortices; the critical currents for each dynamical phase are identified. The structure and trajectory of the vortex core motion in each magnetic layer are studied for the case of the vortex polarity switching in a thick layer. We show that the vortex polarity switching process has a dynamic nature and is associated with a vortex-antivortex pair formation.

Control of magnetic vortex polarity by the phase difference between voltage signals

Using micromagnetic simulations, we investigate the voltage control of magnetic vortex polarity based on a designed multiferroic heterostructure that contains two separate piezoelectric films beneath a magnetostrictive nanodisk. The results show that controllable switching of vortex polarity can be achieved by proper modulation of the phase difference between two sinusoidal voltage pulses V1 and V2, which are applied to the two separate piezoelectric films, respectively. The frequencies of V1 and V2 are set at the gyrotropic eigenfrequency fG of the nanodisk, and the vortex polarity switching is completed via the nucleation-annihilation process of the vortex-antivortex pair. Our findings provide an additional effective means for ultralow power switching of the magnetic vortex, which lays the foundation for voltage-controlled vortex random access memory.

Indirect switching of vortex polarity through magnetic dynamic coupling

Magnetic vortex cores exhibit a gyrotropic motion and may reach a critical velocity, at which point they invert their z-component of the magnetization. We performed micromagnetic simulations to describe this vortex core polarity reversal in magnetic nanodisks with a perpendicular anisotropy. We found that the critical velocity decreases with the increase in perpendicular anisotropy, therefore departing from a universal criterion that relates this velocity only to the exchange stiffness of the material. This leads to a critical velocity inversely proportional to the vortex core radius. We have also shown that in a pair of interacting disks, it is possible to switch the core vortex polarity through a non-local excitation; exciting one disk by applying a rotating magnetic field, one is able to switch the polarity of a neighbor disk, with a larger perpendicular anisotropy.

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 deformation of 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.

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.

Multiple vortex-antivortex pair generation in magnetic nanodots

The interaction of a magnetic vortex with a rotating magnetic field causes the nucleation of a vortex--antivortex pair leading to a vortex polarity switching. The key point of this process is the creation of a dip, which can be interpreted as a nonlinear resonance in the system of certain magnon modes with nonlinear coupling. The usually observed single-dip structure is a particular case of a multidip structure. The dynamics of the structure with $n$ dips is described as the dynamics of nonlinearly coupled modes with azimuthal numbers $m=0,\pm n,\pm 2n$. The multidip structure with arbitrary number of vortex antivortex pairs can be obtained in vortex-state nanodisk using a space- and time-varying magnetic field. A scheme of a possible experimental setup for multidip structure generation is proposed.

Controllable vortex polarity switching by spin polarized current

Nanopillars containing a perpendicular polarizer and a vortex free layer have been considered as promising structures for the selective switching of the vortex core by changing the spin polarized current direction. In this paper, two distinct switching routes of the vortex cores are found to be classified according to the lateral dimension of samples. For a relatively large element, the core polarity is switched through a creation and annihilation process of vortex-antivortex pair and the vortex circulation remains unchanged; however, for a small element, the core switching is mediated by a transient C-state, and moreover, the circulation is dominated by the current-generated Oersted field.

Switching phenomena in magnetic vortex dynamics

A magnetic nanoparticle in a vortex state is a promising candidate for information storage. One bit of information corresponds to the upward or downward magnetization of the vortex core (vortex polarity). The generic properties of the vortex polarity switching are insensitive to the way that the vortex dynamics has been excited: by an ac magnetic field, or by an electrical current. We study theoretically the switching process and describe in detail its mechanism, which involves the creation and annihilation of an intermediate vortex-antivortex pair.

Transmutation of momentum into position in magnetic vortices

We show that transmutation of linear momentum into position may occur in a system of three magnetic vortices thanks to a direct link between topology and dynamics in a ferromagnet. This happens via an exchange between the linear momentum of a vortex–antivortex (VA) pair and the position of a single vortex during a semi-elastic scattering process. Vortex polarity switching occurs in the case of inelastic collisions.

Current induced switching of vortex polarity in magnetic nanodisks

It is shown that the vortex polarity can be irreversibly switched by injecting a spin-polarized direct electrical current, which flows perpendicular to the disk plane. Intensive numerical spin-lattice simulations demonstrate that the switching process involves a vortex-antivortex pair creation. This differs from magnets with no dipolar interaction, where the spin dc acts similar to a static magnetic field.

Vortex Polarity Switching by a Spin-Polarized Current

The spin-transfer effect is investigated for the vortex state of a magnetic nanodot. A spin current is shown to act similarly to an effective magnetic field perpendicular to the nanodot. Then a vortex with magnetization (polarity) parallel to the current polarization is energetically favorable. Following a simple energy analysis and using direct spin-lattice simulations, we predict the polarity switching of a vortex. For magnetic storage devices, an electric current is more effective to switch the polarity of a vortex in a nanodot than the magnetic field.