Search results for "MAGNETIC FIELD"

Study of the dynamical approach to the interface localization–delocalization transition of the confined Ising model

2004

Confined magnetic Ising films in a L ? D geometry (), with short-range competing magnetic fields?(h) acting at opposite walls along the D-direction, exhibit a slightly rounded localization?delocalization transition of the interface between domains of different orientations that runs parallel to the walls. This transition is the precursor of a wetting transition that occurs in the limit of infinite film thickness () at the critical curve Tw(h). For T Tw(h)) such an interface is bounded (unbounded) to the walls, while right at Tw(h) the interface is freely fluctuating around the centre of the film. Starting from disordered configurations, corresponding to , we quench to the wetting critical t…

A coupled-map model for the magnetotail current sheet

1999

A magnetic field model of the magnetotail current sheet in the form of a coupled-map lattice (CML) is presented. It is a continuously driven and based on the MHD diffusion equation. Solar wind vBs data (solar wind speed multiplied by the southward component of IMF) are used for driving the model, and it is shown to exhibit perturbations (avalanches) with power-law scalings in their distributions of duration and size. Such distributions may indicate self-organized critical (SOC) behavior. Furthermore, it is shown that the power spectra of the model outputs are of bicolor power-law form with different slopes for high and low frequencies. The model parameters determine the frequency of the bre…

2021

The idea of remote magnetic guiding is developed from the underlying physics of a concept that allows for bijective force generation over the inner volume of magnet systems. This concept can equally be implemented by electro- or permanent magnets. Here, permanent magnets are in the focus because they offer many advantages. The equations of magnetic fields and forces as well as velocities are derived in detail and physical limits are discussed. The special hydrodynamics of nanoparticle dispersions under these circumstances is reviewed and related to technical constraints. The possibility of 3D guiding and magnetic imaging techniques are discussed. Finally, the first results in guiding macros…

Photoluminescence structure of highly excited quantum dots of type II

2007

Abstract The photoluminescence (PL) due to decay of exciton-like e–e–h complex X– (expected to appear for higher levels of activation) in electrically defined quantum dots of type II is analyzed within the Hartree approach for Gaussian confining potential, where the existence of metastable (against far-infrared interband dipole transitions) states is predicted, due to interplay of bare confinement with Coulomb interaction between the carriers. As we will show, when three-particle complexes (e–e–h) are taken into account, three PL peaks can occur at zero magnetic field, which further split into four peaks when external magnetic field is applied, which stands in a good correspondence with the…

Effect of external magnetic field on angular momenta distribution

1995

Local control of domain wall dynamics in ferromagnetic rings

2015

Ferromagnetic nanorings are of great interest due to prospective applications in memory and logic devices based on domain wall (DW) motion.1-3A key-prerequisite for their realization is a reproducible domain wall spin structure with a well-controllable wall velocity. We have found that DW propagation in magnetic ring is characterized by non-constant vortex DW velocity even below Walker breakdown4 (as opposed to straight wires). Several studies have been devoted to the optimization of ring reversal on a global scale using out-of plane field5 or flux charges emanating from neighboring rings if placed in close proximity6. However, these methods involve DW pinning and vortex nucleation processe…

Electric field driven domain wall transfer in hybrid structures

2012

Domain wall (DW) motion devices attracts much interest with their prospective logic and memory applications[1][2]. Present on-chip DW manipulations by a magnetic field of electric currents or electron spin torque raise the problem of high Ohmic energy losses. We show that such a difficulty can be avoided by applying an exchange field H eff to the magnetic layer from the proximate graphene (Gr), instead of using an actual magnetic field. H eff is shown to be dependent on carrier density gradient in Gr, which is easily manipulated with a gate voltage. A novel memory device implementing this concept is designed and modeled, demonstrating switching power well below femto-Joule while maintaining…

Automotive domain wall propagation in ferromagnetic rings

2015

Automotive domain wall propagation is a self-propelling motion utilizing the energy stored in a particular energy reservoir of the spin structure to speed up domain wall beyond its equilibrium value given by external driving force and damping. Such a concept of DW motion is of great interest due to recent development of spintronic devices based on domain walls, where automotion could be used to assist or prevent domain wall pinning at low driving fields1-2. In turn, most of studies so far have been devoted to the automotion invoked by DW transformations from metastable to stable states3-4; appearing at sufficiently high magnetic fields strong and enough to trigger domain wall spin structure…

Dynamic domain wall chirality rectification by rotating magnetic fields

2015

We report on the observation of magnetic vortex domain wall chirality reversal in ferromagnetic rings that is controlled by the sense of rotation of a magnetic field. We use time-resolved X-ray microscopy to dynamically image the chirality-switching process and perform micromagnetic simulations to deduce the switching details from time-resolved snapshots. We find experimentally that the switching occurs within less than 4 ns and is observed in all samples with ring widths ranging from 0.5 μm to 2 μm, ring diameters between 2 μm and 5 μm, and a thickness of 30 nm, where a vortex domain wall is present in the magnetic onion state of the ring. From the magnetic contrast in the time-resolved im…

Energy oscillations and a possible route to chaos in a modified Riga dynamo

2010

Starting from the present version of the Riga dynamo experiment with its rotating magnetic eigenfield dominated by a single frequency we ask for those modifications of this set-up that would allow for a non-trivial magnetic field behaviour in the saturation regime. Assuming an increased ratio of azimuthal to axial flow velocity, we obtain energy oscillations with a frequency below the eigenfrequency of the magnetic field. These new oscillations are identified as magneto-inertial waves that result from a slight imbalance of Lorentz and inertial forces. Increasing the azimuthal velocity further, or increasing the total magnetic Reynolds number, we find transitions to a chaotic behaviour of th…