Surface antiferromagnetic domain structures of NiO (0 0 1) studied using UV photoemission electron microscope

Direct observation of the antiferro (AF) magnetic domain structures of a NiO (0 0 1) surface is found to be possible using a spectroscopy photoelectron low-energy electron microscope (SPELEEM) and a commercial UV Hg excitation light source without using any polarizers. The principle is based on the magnetic linear dichroism (MLD) effect, where different domain contrasts are produced according to the relative angle between the antiferromagnetic axis and the linearly polarized light. The observed AF magnetic domain structures are strongly affected by both bulk AF magnetic domain structures and the stresses induced during the sample cleaving process. Moreover, the AF magnetic domain structures are found to be irreversible when the sample is heated to over its Néel temperature and then cooled. The possibility of imaging AF magnetic domain structures without using synchrotron radiation or a polarizer is attractive.     

Kinetics of domain wall pinning in an incommensurate Pb overlayer on a Cu(110) surface

We have used grazing incidence X-ray scattering to study the kinetics of domain wall pinning during the transition between an incommensurate phase and a domain wall glass phase. The growth of both domain wall density and domain size are described by power-laws. The results are discussed in the context of recent theoretical models of growth.     

Amorphization of biperiodic domain structures in quasi-uniaxial magnetic films with a critical thickness

The behavior of biperiodic stripe domain structures in quasi-uniaxial magnetic films with a near-critical thickness is studied by scanning magnetic force microscopy and magnetooptical diffraction. In these films, antiphase and hybrid biperiodic domain structures are found to be absent, and the phase transitions between monoperiodic and in-phase biperiodic domain structures are shown to proceed through two-dimensional domain arrays that are amorphized in the arrangement of near-surface distortions in the domain-wall profile.     

Mode spectrum of noncollinear electroacoustic boundary-guided waves in a ferroelectric with a moving strip domain

The mode spectrum of electroacoustic boundary waves guided by a strip domain uniformly moving in a 4-mm ferroelectric is considered in the quasi-static approximation. The motion of the strip domain is found to cause the wave vector of the electroacoustic wave to be noncollinear with the guiding boundaries. The frequency dependences of the phase velocity are presented for the symmetric and antisymmetric modes of the electroacoustic wave. These dependences are compared in the reference system fixed to the strip domain and in the laboratory reference system. It is shown that, at low and moderate frequencies, the symmetric mode of the electroacoustic wave is more efficiently localized by a moving strip domain than by a single domain wall.     

Quantum tunneling of a Bloch line in the domain wall of a cylindrical magnetic domain

Tunneling through a vertical Bloch line (BL) defect in the domain wall of a cylindrical magnetic domain is considered. It is shown that the BL tunneling probability and the corresponding crossover temperature are determined by the vibrational spectrum of the domain. The parameters characterizing this effect are estimated for a state of the domain close to the elliptical instability state.     

Tunable conductance of magnetic nanowires with structured domain walls

We show that in a magnetic nanowire with double magnetic domain walls, quantum interference results in spin-split quasistationary states localized mainly between the domain walls. Spin-flip-assisted transmission through the domain structure increases strongly when these size-quantized states are tuned on resonance with the Fermi energy, e.g., upon varying the distance between the domain walls which results in resonance-type peaks of the wire conductance. This novel phenomenon is shown to be utilizable to manipulate the spin density in the domain vicinity. The domain wall parameters are readily controllable, and the predicted effect is hence exploitable in spintronic devices.     

Domain reversal behavior in perpendicular magnetic nanothin films

We report domain reversal behavior in perpendicular ferromagnetic nanothin films investigated by means of a novel magneto-optical microscope magnetometer, capable of grabbing domain reversal patterns in real time under an applied field as well as simultaneous measurements of 8000 local hysteresis loops with 400-nm special resolution. Three contrasting domain reversal behaviors are found to exist: wall-motion dominant, dendritic-growth dominant, and nucleation dominant reversal. Quantitative analysis reveals that the contrasting reversal behavior is mainly caused by a sensitive change in wall-motion speed and that the reversal ratio of wall-motion speed over nucleation rate is a governing parameter for the contrasting domain reversal dynamics. The activation volumes of the wall-motion and nucleation processes are found generally unequal, and the inequality is closely related with the domain dynamics. The domain reversal pattern is truly coincident with submicron-scale local coercivity variation and local switching time of domain evolution is exponentially dependent on local coercivity governed by a thermal activation relaxation process. The observed domain reversal behavior could be well predicted by a Monte Carlo simulation of a micromagnetic model based on the uniaxial magnetic anisotropy of nanothin films.     

Ferroelectric domain structure of SrBi2Nb2O9 epitaxial thin films

The domain structure in a ferroelectric with well-defined crystallography and negligible ferroelastic distortion (<0.002%) is reported. In contrast to prototypical ferroelectrics in which long-range elastic strain dictates the domain structure, in SrBi2Nb2O9 the elastic term is insignificant, allowing dipole-dipole interactions and domain wall energies to dominate in determining the domain structure. Electron microscopy reveals ferroelectric domains that are irregularly shaped and highly curved. Out-of-phase boundary defects are shown to be weakly correlated with 90 degrees ferroelectric domain structure.     

Fundamental Equations of Quantum Mechanics in Time-Varying Domain

Fundamental equations of quantum mechanics in time-varying domain are presented. The used method consists in transforming the variable domain into a fixed domain. The transformation has to be covariant in relation to the wavefunction. The new fundamental equations turn out to be a generalization of the classical equations established in a Newtonian space-time. When the time-varying domain becomes stationary, we find again the fundamental equations of the classical quantum mechanics.     

纳米接触行为的三维多尺度数值模拟

应用分子动力学与有限元耦合的桥域多尺度算法,模拟三维刚性球形压头与光滑基体表面的纳米尺度接触行为,并与全原子分子模拟结果比较.考察在一定载荷下的系统弛豫行为、两种模型桥接区位移和应力的连续性、法向力和接触面积随压头位移变化等,结果表明:一定外载荷下,桥域多尺度算法能较快达到平衡状态,且压头的振荡幅度更小,系统初始温度为0 K时该算法的相对误差最小.在准静态加载过程中,该算法能够将原子区的位移、应力等连续的过渡到连续介质区,具有较好的耦合效果;法向力-压头位移和接触半径-压头位移曲线几乎与分子模拟结果重合,表明算法具有较高的计算精度.     

Study of the specific features of lithium niobate crystals near the domain walls

The domain walls in LiNbO₃ are studied using X-ray topography, X-ray diffraction, and scanning electron microscopy. It is shown that the regions of distortions of the crystal lattice near the domain walls of different types are different and have lateral sizes of 100–200 μm. The character and the magnitude of the distortions are substantially dependent on the method of formation of the domain structure. Under irradiation in a scanning electron microscope, the crystal region up to 25 μm in width near the “tail-to-tail” domain walls is charged more slowly and, unlike the “head-to-head” domain walls, exhibits a dynamic charge image in the secondary-electron regime.     

Dynamics of magnetic domain wall motion after nucleation: dependence on the wall energy

The dynamics of magnetic domain wall motion in the FeNi layer of a FeNi/Al2O3/Co trilayer has been investigated by a combination of x-ray magnetic circular dichroism, photoelectron emission microscopy, and a stroboscopic pump-probe technique. The nucleation of domains and subsequent expansion by domain wall motion in the FeNi layer during nanosecond-long magnetic field pulses was observed in the viscous regime up to the Walker limit field. We attribute an observed delay of domain expansion to the influence of the domain wall energy that acts against the domain expansion and that plays an important role when domains are small.     

W(110)基底上的铁纳米岛初始自发磁化态的微磁学模拟

用微磁学模拟研究W(110)基底上铁纳米岛的初始自发磁化态的磁畴结构,确定了不规则形状、椭圆形和矩形岛中不同磁畴态之间的各向异性常数的临界点,得到了纳米岛的磁化态作为各向异性常数和厚度函数的完整相图,相图中存在一较宽的过渡区,把双畴态与涡旋态和菱形态分开,过渡区两侧的边界是不确定的.计算结果表明,初始自发磁化态的磁畴结构主要由各向异性及岛的厚度决定,而且岛的边沿形状对涡旋态和菱形态的磁畴结构有重要影响.准确的铁纳米岛的各向异性常数仍有待于进一步确定. 关键词： 初始自发磁化磁畴结构 铁纳米岛 微磁学模拟 各向异性     

The effect of stripe domain structure on dynamic permeability of thin ferromagnetic films with out-of-plane uniaxial anisotropy

The permeability is calculated for a thin ferromagnetic film with the stripe domain structure and out-of-plane uniaxial magnetic anisotropy. Analytical expressions for the frequency dependence of components of permeability tensor are derived with the use of the Smit–Beljers method, with the thickness of domain walls and the domain wall motion being neglected. The effect of the domain width and the angle between the anisotropy axis and the film plane on the frequency dependence of the permeability is analyzed. General equations relating the static permeability components and the ferromagnetic resonance frequencies are found. The results of the approach are applied to the derivation of the constraint for the microwave permeability of thin ferromagnetic films. The analysis of the constraint as a function of the axis deviation angle, the domain aspect ratio and the damping parameter allows the conditions to be found for maximal microwave permeability. The results obtained may be useful in connection with the problem of developing high-permeable microwave magnetic materials.     

Effect of domain walls on the propagation of microwaves

The propagation of microwaves in ferrimagnets is affected mainly by the gyrotropic terms of the magnetic permeability tensor, due in this frequency range to ferromagnetic and exchange resonances. It is shown that the change in the gyrotropic terms in the domain wall region leads to the existence of a localized mode propagating close to the domain wall. The domain wall constitutes an optical inhomogeneity for the microwave. The reflectivity and transmittivity of a domain wall are calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 22–26, June, 1985.The authors are grateful to G. S. Krinchik for discussion of the paper.     

High-temperature memory in multiferroic cobalt–bromine boracite

The observation of the domain dynamics of the ferroelectric–ferroelastic domains near the paraelectric–ferroelectric phase transition is reported. The study was performed by means of high-temperature polarized light microscopy. Close to the phase transition an increase in the number of domain walls was observed. After several heating–cooling cycles around the transition temperature, a memory domain microstructure at high temperature was observed. The possible physical mechanisms responsible for the high-temperature domain dynamics are discussed. Using a complex systems approach the complexity of the domain behavior is characterized.     

Magnetization reversal in (0 0 1)Fe thin films studied by combining domain images and MOKE hysteresis loops

The magnetization reversal of epitaxial single-crystal Fe films has been studied by combining domain images and hysteresis loops. The reversal is quantitatively described by combining the coherent rotation model and the domain wall displacement model. The pinning energy exerted on the domain walls and the domain wall angle at the switching fields are obtained by fitting this model to experimental hysteresis loops. The field-dependent pinning energy and the domain wall angle in the reversal process, and the contributions of second-order magneto-optic effect to hysteresis loops, are revealed to be two important features of single-crystal Fe films.     

LETTER: Gauge Field Corrections to Domain Walls

Gauge field corrections to domain walls are obtained by making use of perturbation method on the usual flat domain wall. The gauge vector field introduces a damping term and an external force on the motion equation for the perturbed domain wall. A thin domain wall approximation solution is found. The vector gauge field also introduces a gauge mass term correction into the perturbed Lagrangean.     

Transient domain wall displacement under spin-polarized current pulses

This paper investigates the non steady-state displacement of magnetic domain walls in a nanostrip submitted to a time-dependent spin-polarized current flowing along the nanostrip. First, numerical micromagnetic simulations show that a domain wall can move under application of a current pulse, and that the displacement resulting from a conversion of the domain wall structure is quantized. The numerical findings are subsequently explained in the framework of simplified analytic models, namely the 1D model and the point-core vortex model. We then introduce the concept of an angle linked to the magnetization of a general domain wall, and show that it allows understanding the transient phenomena quite generally. Simple analytic formulas are derived and compared to experiments. For this, charts are given for the key parameters of the domain wall mechanics, as obtained from numerical micromagnetic simulations. We finally discuss the limitations of this work, by looking at the influence of temperature elevation under current, presence of a non-adiabatic term, and of disorder.     

Periodic domain structures in stoichiometric lithium niobate: Formation by electron beam

The formation of periodic domain structures in stoichiometric lithium niobate crystals via direct surface irradiation using a controllable electron beam in a scanning electron microscope is studied. The periodic domain structures are fabricated at different microscope parameters (current, voltage, charge density) and different ways of charge implantation. The irradiation modes for the formation of uniform periodic domain structures are experimentally found. The use of optimal electron-beam parameters and ways of crystal surface irradiation make it possible to fabricate domain structures with a period of 6.9 μm in a crystal 0.5 mm thick. Domain structures of this kind can be used for optical wavelength conversion by quasi-phase-matching and second harmonic generation in lithium niobate.