Dynamic Behavior Of Domain Walls Research Articles

Static and dynamic behavior of domain walls in high BS soft magnetic ribbons tuned by the annealing temperature

In this paper, we study the domain wall dynamics in high magnetic flux density (–1.85 T) of soft magnetic ribbons Fe81.2Co4Si0.5B9.5P4Cu0.8 prepared with various annealing conditions. It is observed that annealing these ribbons beyond a temperature (C) crystalizes the alloy with the appearance of α-Fe(-Co) phase. The post annealing leads to a change from amorphous to nanocrystalline phase accompanied by a reduction in internal stress in the ribbons. Domain imaging has been performed under both dc and ac fields to study the domain wall behavior in these ribbons. A wide variety of domain structures are observed in ribbons prepared with different annealing temperature as a result of the change in the intrinsic anisotropy. Under an ac magnetic field, the ‘stress patterns’ in the amorphous ribbons are robust. However, ribbons with reduced stress (i.e. nanocrystalline) exhibit domain wall propagation which hints at a significant reduction in magnetocrystalline and magnetoelastic anisotropies due to uniform nanocrystallization. The ribbon annealed at C exhibits static domain patterns resulting from strong pinning centers created by Fe-B precipitates.

Nonlinear nonstationary dynamics of Néel domain walls in ultrathin films with an in-plane anisotropy

Nonlinear dynamic behavior of domain walls in ultrathin films (of thickness b < bt, where bt is a critical thickness below which only one-dimensional Neel walls exist in the stable state) has been investigated based on the numerical solution of the Landau-Lifshitz equation with an exact (modelless) allowance for all principal interactions, including dipole-dipole one (in the continuum approximation), in terms of a two-dimensional distribution of magnetization. It is shown that at film thicknesses close to bt the nonlinear dynamic transformation of the Neel-wall structure occurs through the formation of vortex structures. In thinner films, the mechanism of the dynamic rearrangement of the wall proves to be similar to that in unbounded samples. Giant oscillations of the thicknesses of the domain walls in the process of their motion have been revealed. A monotonic decrease in the critical field with increasing b and its nonmonotonic dependence on the saturation induction have been found. The dependences of the period of dynamic transformations of the wall structure on the magnetic parameters and film thickness have been revealed.

Effect of a pulsed magnetic field on the nonlinear dynamics of vortexlike domain walls in magnetic films

The Landau-Lifshitz equation is numerically solved to study the nonlinear dynamic behavior of domain walls with the 2D vortexlike magnetization distribution in magnetically uniaxial films that have in-plane anisotropy and are exposed to a pulsed magnetic field. It is shown that a pulsed magnetic field Hp may induce transitions between various steady wall motions that differ in magnetization distribution. Solitary rectangular pulses, as well as a regular train of rectangular pulses, may be used to control the period of nonlinear dynamic transformations of the wall internal structure and the related period of variation of the wall velocity.

An In-Situ Tem Study of the Dynamic Behavior of Domain Walls in a Free-Standing Lead Titanate Thin Film Under External Stress

AbstractThe evolution of domain structure with external stress in a free-standing PbTiO3 ferroelectric thin film of ˜100nm in thickness is observed by in-situ TEM technique. The thin film is composed of granular grains of ˜100nm in diameter, most of them appear to be single-domained whereas others are multi-domained showing domains of different sizes(5˜20nm). For some single-domained grains new domains appear during tension. For multi-domained grains, rearrangement of domain walls and coarsening of domains have been observed during tension. In many cases the domain walls disappear under high stress, i.e., a multi-domained grain changes into a single-domained grain. However, it is also observed that a large portion of single-domained grains appear not to respond to external stress. The dynamic behavior of domain walls in very thin ferroelectric thin films may help to understand the switching of these very thin films.

Dynamics of Stripe Domain Walls in Bubble Films

Computer simulations of the dynamic behavior of domain walls in bubble films, for use in the development of the different functions of Bloch line memories, are commonly based on the domain wall model developed by Slonczewski. To investigate the degree of reliability of this wall model, we compared numerical results of the dynamics of an infinitely long, straight stripe domain with stripe translation measurements, where drive pulses of the order of 2 to 10 Oe and 50 to 200 nsec were applied, and the total displacement of the stripe, including overshoot, was measured. Numerical and experimental results for the total displacement agree well for drive fields below the experimentally determined breakdown field. The values obtained for the breakdown field also agree well in most cases; however, the discrepancy increases with increasing film thickness and drive field strength. Another discrepancy is the numerical result of a strong dependence of the stripe velocity on the drive field after breakdown in the case of thicker films, which was not observed in experiments. Both discrepancies are thought to result from implicit limitations of the wall model.

Dynamic behavior of domain walls in double layer self-biasing bubble garnet films

Radial expansion of bubbles and gradient bubble propagation experiments were conducted in a double layer garnet film with perpendicular anisotropy in both layers. Implanted and as-grown samples are compared. In radial expansion the side walls of the bubble exhibit a linear mobility much lower than calculated from γΔ/α. Saturation occurs at high drives (35 Oe). At drives above 50 Oe the saturation velocity of 27 m/s occurs only in the first 120 ns of the motion. After that the velocity drops to 17.5 m/s still independent of drive. This break in velocity does not occur in implanted samples, where the saturation velocity depends on implantation conditions. In gradient propagation saturation occurs at fields an order of magnitude smaller. The saturation velocity is independent of implantation, but overshoot depends strongly on it. No creep was detected. The 180° head-on domain wall between the two layers is found to have little effect on the dynamics of the side walls of the bubble. The motion of the head-on wall is also investigated and its velocity estimated. This head-on wall exhibits a linear mobility and a saturation velocity at high drives.

Dynamic behavior of domain walls in thin magnetic films

The structure of moving domain walls is obtained by maximizing a Lagrange function, assuming that the film has a uniaxial anisotropy axis in the plane of the film. The variational calculation is based on a class of trial functions previously used for the static case of Dietze and Thomas. The solution applies for wall velocities smaller than a certain critical velocity. At the critical velocity the derivative of the wall energy with respect to velocity becomes infinite and the energy remains finite. For very thick and very thin films the critical velocity calculated with the chosen trial function approaches the critical velocity for bulk material to within one percent. At intermediate film thicknesses, near the transition from a Bloch to a Néel wall, the critical velocity is much smaller (approximately 1/20 of the bulk value in the case of Permalloy). The effective mass per unit area of the wall increases with increasing film thickness for Néel walls and decreases for Bloch walls. This dependence is qualitatively similar to that of the inverse (static) wall width on film thickness, but considerably stronger. Néel walls and Bloch walls in thick films contract with increasing velocity. At intermediate film thicknesses a region exists in which Bloch walls expand slightly with increasing velocity.

Dynamic behavior of domain walls in yttrium-gallium-iron garnets

Dynamic behavior of domain walls in yttrium-gallium-iron garnets

Domains and domain-wall motion in grain-oriented 50-percent Ni-Fe tapes

Domains and domain-wall motion in grain-oriented 50-percent Ni-Fe tapes were studied using a Kerr magnetooptical apparatus. The domain walls were quite straight under a slowly increasing field, and the nucleation of a reversed domain always occurred at either or both sides of the tapes. The 90° walls, such as those observed in a single crystal, often appeared even in the samples which were not strained to conserve the magnetization continuity. Under pulse fields the nucleation sites of reversed domains were distributed on the tape surface, and many isolated small domains appeared. It was found, however, that the domain configurations under the successive pulse field drive of much shorter length were similar to those under a slowly increasing field. Domain-wall velocities were measured for the samples of the thickness range from 25 μm to 81 μm, keeping the distance of wall displacement nearly constant by setting properly the pulse field amplitude and length. The measured dependence of the velocity on pulse field amplitude was not linear, and the mobilities increased with increasing field amplitude. This is discussed from the dynamic behavior of domain walls in tapes.

Dynamic Behavior of Domain Walls in Barium Titanate

The nucleation and growth of 90\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{} domains in barium titanate single crystals have been measured with optical techniques. Both types of domains nucleate as long thin wedges with an initial velocity of the order of ${10}^{4}$ cm/sec for a driving field of 5 kv/cm. For 90\ifmmode^\circ\else\textdegree\fi{} domains, detailed measurements of the nucleation rate as a function of time and field strength are given. After domains have been introduced into a crystal, their growth may be described in terms of wall motion. The 90\ifmmode^\circ\else\textdegree\fi{} wall displacement depends strongly on strains and clamping of the crystal; wall motion appears to cease for frequencies in the megacycle range, where the piezoelectric resonances of the crystal set in. The sideways growth of 180\ifmmode^\circ\else\textdegree\fi{} wedges is affected by the availability of neutralizing electric charges. Interaction of 180\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{} domains may lead to 90\ifmmode^\circ\else\textdegree\fi{} wall configurations with head-to-head or tail-to-tail orientation of the polar axes.