Microstructure and bloch wall arrangement in 22 NiMoCr 3 7 steel

Starting from a simulated structural condition typical for the coarse-grained heat affected zone of welding joints, the changes of microstructure (residual stresses, grain structure, dislocations and precipitates) and of the arrangement of Bloch walls and domains caused by isothermal tempering (610°C/0.1–150 h) were examined using transmission electron microscopy. In the same way, the water quenched material (as-received) was also examined. The micrographs show that the arrangement of Bloch walls became clearer with increasing tempering time. This is correlated with a decrease in the dislocation density caused by recovery and recrystallization processes. Differences of the mobility of Bloch walls and the area traversed by single jumps of Bloch wall segments could be observed.     

Static properties of asymmetric vortex-like domain walls in magnetically uniaxial thick films

The structure and energy of asymmetric vortex-like Bloch and Néel walls in a magnetically uniaxial film with an easy magnetization axis lying in the film plane are investigated by numerically minimizing the total energy within the rigorous micromagnetic approach and the two-dimensional model of the magnetization distribution. The calculations are performed over wide ranges of film thicknesses b (up to b = 1 μm) and magnetic parameters of the films. It is established that the asymmetric vortex-like domain walls are the most universal wall structures in the films under consideration. In magnetically uniaxial films, unlike in magnetically multiaxial films, the asymmetric Bloch walls are always stable.     

Generation of mesoscopic magnetic structures by local laser action

New effects are observed wherein the internal structure of the domain walls in a thin magnetic iron garnet film are modified by the action of focused laser radiation. A single laser pulse with increasing power gives rise to the following: 1) displacement of vertical Bloch lines in a domain wall; 2) generation of a pair of vertical Bloch lines on initially line-free walls; and, 3) an irreversible change in shape of a domain wall and the domain structure as a whole. The mechanism leading to the generation and displacement of Bloch lines is connected with the motion of domain walls which is induced by a local change in the distribution of demagnetizing fields as a result of a heating-induced decrease of the magnetization in the focal spot of the laser radiation. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 398–402 (25 September 1997)     

Interaction between superconducting vortices and a Bloch wall in ferrite garnet films

A theoretical model for how Bloch walls occurring in in-plane magnetized ferrite garnet films can serve as efficient magnetic micromanipulators is presented. As an example, the walls' interaction with Abrikosov vortices in a superconductor in close contact with a garnet film is analyzed within the London approximation. The model explains how vortices are attracted to such walls, and excellent quantitative agreement is obtained for the resulting peaked flux profile determined experimentally in NbSe(2) using high-resolution magneto-optical imaging of vortices. In particular, this model, when generalized to include charged magnetic walls, explains the counterintuitive attraction observed between vortices and a Bloch wall of opposite polarity.     

Experimental evidence of the magnetic moment of Bloch walls in garnet films

Differential susceptibility measurements in low in-plane fields showed up a new peak assumed to be caused by magnetization reversal inside the Bloch walls (BW). Highly sensitive measurements carried out subsequently on different domain structures yielded various new parameters such as the BW hysteresis curve, the integral saturated and remanent BW moments and the internal BW coercivity. The mechanism proposed for the observed phenomena is based on the reversible and irreversible motion of Bloch lines inside the Bloch walls.     

Transition micromagnetic structures in asymmetric vortexlike domain walls (Static solutions and dynamic reconstructions)

The possible types of transition structures with a three-dimensional magnetization distribution over regions in the vortex asymmetric domain walls that exist in magnetically uniaxial soft magnetic films with in-plane anisotropy are studied by computer simulation in terms of a micromagnetic approach. It is shown that the possible structure types include both the type of vertical Bloch lines that was discussed earlier in other works and new types, namely, singular (Bloch) points and clusters consisting of vertical Bloch lines and Bloch points. The spatial configurations of the transition structures are calculated and their topological properties are found. The numerical simulation of the dynamics of closely spaced substructure regions reveals various scenarios of their interaction, including annihilation accompanied by energy release and the excitation of nonlinear waves.     

Domain walls and ising-BLOCH transitions in parametrically driven systems

Parametrically driven systems sustaining sech solitons are shown to support a new kind of localized state. These structures are walls connecting two regions oscillating in antiphase that form in the parameter domain where the sech soliton is unstable. Depending on the parameter set the oppositely phased domains can be either spatially uniform or patterned. Both chiral (Bloch) and nonchiral (Ising) walls are found, which bifurcate one into the other via an Ising-Bloch transition. While Ising walls are at rest Bloch walls move and may display secondary bifurcations leading to chaotic wall motion.     

Classical one-dimensional uniaxial ferromagnets: Role of Bloch walls in statistical mechanics

We study the conceptual features lying in low-temperature thermodynamic quantities of classical one-dimensional uniaxial ferromagnets. The phenomenological statistical mechanics of an ensemble of Bloch walls is shown to reproduce the non-spin wave part of the free energy obtained analytically on the basis of the functional integral methods. The longitudinal correlation length, which shows the Ising-like behaviour, is found inversely proportional to the concentration of Bloch walls.     

On the domain structure of thin ferromagnetic films

The energy of Bloch walls is calculated for very thin ferromagnetic films with respect to the demagnetizing energy of a Bloch wall. A model of the stability of the domain structure in thin films is proposed.Part of this paper was delivered at the conference of solid state physics in Sopoty (Poland) November 5–11th, 1956.     

Observation of Bloch lines in yttrium orthoferrite

Utilizing the dark field method, parts of different brightness within domain walls of yttrium orthoferrite have been observed. Dark segments between these parts and the dependence of their positions on an applied magnetic field indicate the presence of Bloch lines.     

Localization of matter and fermion resonances on double walls

We investigate the possibility of localizing various matter fields on the double walls. For spin 0 scalar field, massless zero mode can be normalized on the double walls. However, for spin 1 vector field, the zero mode is not localized on the double walls. In the paper [C.A.S. Almeida, M.M. Ferreira Jr., A.R. Gomes, R. Casana, arXiv:0901.3543 [hep-th]], the authors investigated fermion localization on a Bloch brane, especially, they found fermion resonances on the Bloch brane for both chiralities and related their appearance to branes with internal structure. Inspired by their work, for spin 1/2 spinor field, we focus our attention mainly on the fermion resonances, and also found fermion resonances for both left-handed fermions and right-handed ones on the double walls, which further supports the arguments presented in the paper [C.A.S. Almeida, M.M. Ferreira Jr., A.R. Gomes, R. Casana, arXiv:0901.3543 [hep-th]].     

Magnetic force microscopy studies of domain walls in nickel and cobalt films

A magnetic force microscopy is used to examine the domain walls in nickel and cobalt films deposited by argon ion sputtering. Thin nickel films deposited at high substrate temperatures exhibit coexistent Bloch and Neel walls. Films grown at room temperature display alternative Bloch lines with cap switches. These films agglomerate to form grains after annealed at high temperatures. The film composed of larger grains behaves better nucleation implying magnetic domains of closure, while the film composed of smaller grains exhibits more defects implying alternative Bloch lines. We have also observed domain displacements and cap switches, which occur due to precipitation of particles in small grain size films. Stripe domains are observed for film thicknesses larger than 100 nm. They become zigzag cells when an external field of 1.5 T is applied perpendicular to the surface of the films. This experiment indicates that the domain sizes in thin films and the strip widths for thick films both depend on the square-root of the film thickness, which varies from 5 to 45 nm and from 100 to 450 nm, respectively.     

Bloch domain walls in type II optical parametric oscillators

Evidence of Bloch domain walls in nonlinear optical systems is given. These walls are found in the transverse fields of optical parametric oscillators when the polarization degree of freedom, the cavity birefringence, and (or) dichroism are taken into account. These domain walls arise spontaneously and exhibit defects where Bloch walls of different chirality join together. Two dynamic regimes are found:In the first one the vector field approaches a final homogeneous state, and in the other the walls are continually generated and annihilated. This dynamic behavior is caused by the fact that walls of opposite chirality move spontaneously with opposite velocity.     

Bloch lines in domain walls of antiferromagnets

Approximants describing the substructure of 180° domain walls in antiferromagnets with a high uniaxial anisotropy are derived. The structure and spectrum of Bloch lines separating the parts of domain walls with oppositely directed antiferromagnetic vectors are determined.     

A new method for investigating the domain structure of ferromagnetics

The paper deals with a new method developed for studying the domain structure on the surface of ferromagnetics. In a number of examples it is shown that this method can be successfully used to indicate Bloch walls between domains of spontaneous magnetization; an arrangement enabling the mapping of domain structure is described.     

A theoretical analysis of Bitter-pattern evolution

A theoretical analysis of the bitter-pattern evolution has been formulated basing on a non-interacting particle behaviour. The results permit an estimation of the observed optical contrast produced by the microfield distribution of Bloch walls. Additionally, the information transference concerning the wall width or the fine structure of the walls is discussed.     

Time development of magnetization

A simple model of Bloch wall motion is described for materials in which there exists a magnetic diffusion after-effect. The model is applied to the statistical system of independent Bloch walls. A qualitative explanation of the time development of magnetization in the d.c. magnetic field, based on this model, is given.     

Magnetization reversal in magnetic nanostripes via Bloch wall formation

We present results of micromagnetic simulations of the magnetization reversal in permalloy nanostripes with 5-10 nm thickness and 200-500 nm width under a longitudinal field of 0.4-16 kA m(-1). The data show four distinct field regions: the well-known regions of uniform and oscillating domain wall movement as well as a process with multiple vortices, and finally a new process including Bloch walls and the generation of vortex-antivortex pairs in the inner part of the stripe rather than at the edges. We investigate this process in detail and derive a criterion for the formation of Bloch walls.     

枝状畴的形成及分形维数计算

对于石榴石磁泡薄膜,提出了产生单个枝状畴（MBD)的“低静态偏磁场法”.MBD的形成是与其畴壁内垂直布洛赫线（VBL）的形核相联系的.随着静态偏磁场H_b从“枝状膨胀的临界偏磁场”H[d]的降低,相应的MBD的畴形变得越来越复杂,伴随有几类硬磁泡的相继形成.对MBD进行了分形研究,把线结构维数的计算应用于MBD极其弯曲的畴壁结构,定量地描述了它们的弯曲和分枝程度,并与其畴壁内VBL的形核联系起来. 关键词：     

Micromagnetic model of the Richter-type relaxation in vacancy-doped Fe3O4

Isothermal disaccommodation curves in vacancy-doped magnetite at room temperature show a typical Richter-type behaviour. Magnetic susceptibility decreases asymptotically according to a relaxation time of about 10² s, which is analyzed in terms of a progressive stabilization of the domains walls. The relaxation strength, vacancies and the restoring pressure on the Bloch walls are closely related.