Types Of Domain Walls Research Articles

Ferroelastic domain walls in BiVO4

Analysis of the domain structure is performed using the method of matching strains at the interface and the model of thin domain walls. Equations describing the matching interlayers for crystal lattices are derived and the interlayer parameters are obtained for all possible types of domain walls in BiVO4. It is shown that the matching interlayers have monoclinic symmetry. A difference between the elastic energy of a domain wall and the parameters of adjacent orientation states is revealed.

Domain Walls in Superfluid 3He-B

We consider domain walls between regions of superfluid 3He-B in which one component of the order parameter has the opposite sign in the two regions far from one another. We report calculations of the order parameter profile and the free energy for two types of domain wall, and discuss how these structures are relevant to superfluid 3He confined between two surfaces.

FractionalSzExcitation and Its Boundstate for theS=1/2 Antiferromagnetic Zigzag Spin Chain in a Magnetic Field

We demonstrate that domain-wall type excitations carrying the fractional magnetization S z =±1/3 and their bound state describe the low-energy physics around the 1/3 plateau of the antiferromagnetic zigzag spin chain in the strongly frustrated region. In particular we discuss the relevance of such domain-wall excitations to the characteristic properties of the magnetization curves: the 1/3 plateau accompanying the spontaneous symmetry breaking of the translation, the cusp singularities above and/or below the plateau, and the even-odd effect in the magnetization curve.

Domain wall orientations in ferroelastics and ferroelectrics

This paper concerns the problem of orientations of domain walls in ferroelastic and/or ferroelectric single crystals. They are specified on the basis of elastic compatibility of the neighbouring domains. Results are presented in form of tables, which make it possible to find spontaneous tensors (i.e. strain and polarization) for each domain state in any ferroelastic and/or ferroelectric species. Domain wall orientations are listed in tables for all combinations of domain states. For each domain wall orientation, their charge or neutrality is indicated. Results are summarized in comprehensive table including numbers of possible domain states, domain wall types (W ∞, W f , S) and their charge or neutrality. Domain pairs with non-permissible domain walls (R case) are also specified.

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.

New type of domain walls: Domain walls caused by frustrations in multilayer magnetic nanostructures

Roughness of the interfaces between layers in a multilayer magnetic structure causes frustration of the exchange interaction between spins. Under certain conditions, frustration brings about the formation of domain walls (DWs) of a new type, whose parameters are determined by the competition between different exchange interactions rather than between the exchange and anisotropy energies as is the case with conventional DWs. Such DWs are much sharper than conventional DWs. The conditions under which micro-(nano-) domains arise are considered, and magnetic phase diagrams for ferromagnet-nonmagnetic metal-ferromagnet and ferromagnet-antiferromagnet nanostructures are discussed.

Domain wall contribution to the magnetoresistance of magnetic multilayers

Abstract The domain wall contribution to the resistance was considered. The frustrations induce the new type of domain walls in the magnetic multilayers “ferromagnet-antiferromagnet”. The thickness of such a domain wall is much smaller than that of the common one. It was shown that the electron scattering on these domain walls could give the significant contribution to the giant magnetoresistance.

Magnetostrictive domain walls in antiferromagnetic NiO.

We report high-resolution observations of antiferromagnetic (AF) domain walls at the surface of NiO and determine the typical width of AF walls in this material to be of the order of 150 nm. We observe a number of different types of domain walls, including double walls caused by long-range interaction between walls. We describe the observed wall profiles by a model containing the exchange interaction and magnetostriction as basic ingredients. The good agreement of this model with experiment shows that the formation of walls between antiferromagnetic domains in NiO and their properties are dominated by magnetoelastic interactions.

Domain wall behaviour at constrictions in ferromagnetic ring structures

Direct non-intrusive imaging and magnetoresistance measurements have been employed to investigate the head-to-head domain walls occurring in micrometre-sized NiFe and Co rings. In wide rings vortex head-to-head domain walls are found to be present. These vortex head-to-head walls are repelled by constrictions in structures with notches, but they are pinned in energetically favourable positions adjacent to the notches. For rings with sufficiently large notches, a transverse head-to-head wall can be stabilized in the constriction. The type of domain wall is shown to be easily identifiable using magnetoresistance measurements.

Landau theory of domain walls for one-dimensional asymmetric potentials

Investigation of a great number of physical systems shows that a Landau free energy of the form F(φ)=Hφ+(A/2)φ2+(B/3)φ3+(C/4)φ4 describes a first-order phase transition in an internal or external field H. To study the formation of static domain walls in these systems we include a spatial gradient (Ginzburg) term of the scalar order parameter φ. From the variational derivative of the total free energy we obtain a static equilibrium condition. By solving this equation exactly for different physical parameters and boundary conditions, we obtained different quasi-one-dimensional soliton-like solutions. These solutions correspond to three different types of domain walls between the two different phases which are created in the system. In addition, we obtain soliton lattice (domain wall array) solutions, calculate their formation energy and the asymptotic interaction between the solitons. By introducing certain transformations, we show that the solutions obtained here can be used to study domain walls in other physical systems such as described by asymmetric double Morse potentials. Finally, we apply our results to the specific cases of liquid crystals and the jam phenomena in traffic flows.

Magnetic properties of sputtered soft magnetic Fe–Ni films with an uniaxial anisotropy

The microstructure and magnetic properties of polycrystalline Fe 100− x Ni x films have been studied by X-ray diffraction (XRD) and magnetic moment measurements. In the XRD pattern of Fe–Ni films, the values of area ratio, A(1 1 1)/ A(2 0 0) for the XRD peaks, in the thickness dependence decrease rapidly with increasing film thickness in the films with a bias field applied parallel to the plane in order to introduce uniaxial anisotropy, but the values for the films without the field are nearly constant. The coercivity vs. thickness analyzed by using Néel's formula show that the values for the films with the bias field follow Néel's formula within the thickness range of 40–100 nm, except the range of 10–40 nm. This result indicates that there is a change in domain wall type at the thickness of 40 nm. From the results of thickness and temperature dependence of magnetization analyzed by using some theoretical models, the values of interaction strength between magnetic ions were determined. The electrical resistivity of films is found to be consistent with the Mayadas–Shatzkes model.

Ordering kinetics in an fccA3Bbinary alloy model: Monte Carlo studies

Using an atom-vacancy exchange algorithm, we investigate the kinetics of the order-disorder transition in an fcc A_3B binary alloy model following a temperature quench from the disordered phase. We observe two clearly distinct ordering scenarios depending on whether the final temperature T_f falls above or below the ordering spinodal T_{sp}, which is deduced from simulations at equilibrium. For shallow quenches (T_f>T_{sp}) we identify an incubation time tau_{inc} which characterizes the onset of ordering through the formation of overcritical ordered nuclei. The algorithm we use together with experimental information on tracer diffusion in Cu_3Au alloys allows us to estimate the physical time scale connected with tau_{inc} in that material. Deep quenches, T_f<T_{sp}, result in spinodal ordering. Coarsening processes at long times proceed substantially slower than predicted by the Lifshitz-Allen-Cahn t^{1/2} law. Structure factors related to the geometry of the two types of domain walls that appear in our model are found to be consistent with Porod's law in one and two dimensions.

Variation of domain formation in a 15 nm NiFe layer exchange coupled with NiO layers of different thicknesses

The correlation between ferromagnetic domain formation and exchange bias in a series of NiFe/NiO samples with varying NiO thicknesses has been investigated using the magneto-optic Kerr effect and magnetic force microscopy. Below a critical thickness (15 nm) of NiO, the exchange bias HE is zero and ripple domains exist in the NiFe layer. Above this critical thickness, cross-tie type domain walls appear concurrently with the appearance of exchange bias. Both the number of cross-tie domain walls and the exchange bias increase with an increase in NiO thickness, reaching a maximum at 35 nm NiO, after which both show a gradual decrease. This variation of domain wall formation in the NiFe layer with the NiO thickness possibly reflects the variation of the domain structure in the NiO layer through interfacial exchange coupling.

Domain walls in two-component dynamical lattices.

We introduce domain-wall (DW) states in the bimodal discrete nonlinear Schrödinger equation, in which the modes are coupled by cross-phase modulation (XPM). The results apply to an array of nonlinear optical waveguides carrying two different polarizations of light, or two different wavelengths, with anomalous intrinsic diffraction controlled by direction of the light beam, and to a string of drops of a binary Bose-Einstein condensate, trapped in an optical lattice. By means of continuation from various initial patterns taken in the anticontinuum (AC) limit, we find a number of different solutions of the DW type, for which different stability scenarios are identified. In the case of strong-XPM coupling, DW configurations contain a single mode at each end of the chain. The most fundamental solution of this type is found to be always stable. Another solution, which is generated by a different AC pattern, demonstrates behavior which is unusual for nonlinear dynamical lattices: it is unstable for small values of the coupling constant C (which measures the ratio of the nonlinearity and coupling lengths), and becomes stable at larger C. Stable bound states of DWs are also found. DW configurations generated by more sophisticated AC patterns are identified as well, but they are either completely unstable, or are stable only at small values of C. In the case of weak XPM, a natural DW solution is the one which contains a combination of both polarizations, with the phase difference between them 0 and pi at the opposite ends of the lattice. This solution is unstable at all values of C, but the instability is very weak for large C, indicating stabilization as the continuum limit is approached. The stability of DWs is also verified by direct simulations, and the evolution of unstable DWs is simulated too; in particular, it is found that, in the weak-XPM system, the instability may give rise to a moving DW. The DW states can be observed experimentally in the same parameter range where discrete solitons have been found in the lattice setting.

Even-odd effects in magnetoresistance of ferromagnetic domain walls

Difference in density of states for the spin's majority and minority bands in a ferromagnet changes the electrostatic potential along the domains, introducing the discontinuities of the potential at domain boundaries. The value of discontinuity oscillates with number of domains. Discontinuity depends on the positions of domain walls, their motion or collapse of domain walls in applied magnetic field. Large values of magnetoresistance are explained in terms of spin-accumulation. We suggest a new type of domain walls in nanowires of itinerant ferromagnets, in which the magnetization vector changes without rotation. Absence of transverse magnetization components allows considerable spin accumulation assuming the spin relaxation length, L_S, is large enough.

Magnetic domain walls in single-phase and phase-separated double-exchange systems

We investigate the structure of magnetic domain walls in a classical double-exchange ferromagnet, evaluating domain wall energies and charges. Three different cases are studied: (i) a conventional smooth Bloch wall, (ii) an abrupt Ising-type wall, which is shown to have lower energy at small values of carrier concentration, and (iii) stripe wall, corresponding to the two ferromagnetic domains being separated by a stripe of another, antiferromagnetic, phase. General aspects of energy balance and geometry of phase-separated states are discussed in this context. It is speculated that domain walls of the latter type may be responsible for the unusual transport properties of certain manganate films.

The Raise and Peel Model of a Fluctuating Interface

We propose a one-dimensional nonlocal stochastic model of adsorption and desorption depending on one parameter, the adsorption rate. At a special value of this parameter, the model has some interesting features. For example, the spectrum is given by conformal field theory, and the stationary non-equilibrium probability distribution is given by the two-dimensional equilibrium distribution of the ice model with domain wall type boundary conditions. This connection is used to find exact analytic expressions for several quantities of the stochastic model. Vice versa, some understanding of the ice model with domain wall type boundary conditions can be obtained by the study of the stochastic model. At the special point we study several properties of the model, such as the height fluctuations as well as cluster and avalanche distributions. The latter has a long tail which shows that the model exhibits self organized criticality. We also find in the stationary state a special phase transition without enhancement and with a crossover exponent $\phi=2/3$. Furthermore, we study the phase diagram of the model as a function of the adsorption rate and find two massive phases and a scale invariant phase where conformal invariance is broken.

Domain Wall Interactions and Transformation of Domain Pattern Near the Improper Ferroelastic Phase Transition of K 2 Ba(NO 2 ) 4

The transformation of domain pattern near the improper ferroelastic phase transition of K 2 Ba(NO 2 ) 4 is investigated using the optical polarization method. Instability of orthogonal ferroelastic domains is shown to be due to their interaction with ultra-thin domains corresponding to the third orientation state. These domains become visible only near the phase transition, however, they may also exist at lower temperatures, probably arising from antiphase boundaries. It is demonstrated that permissible ( W -type) domain walls react forming non-permissible domain walls, which disturb the domain pattern. The atomic structure models are proposed for the domain walls of W -type to discuss their stability near the phase transition.

Drift of domain walls of theabtype in weak ferromagnets

The drift motion of 180° domain walls of the ab type in a weak ferromagnet in an elastic stress field created by a sound wave propagating parallel or perpendicular to the plane of the domain wall is investigated. The dependence of the domain-wall drift velocity on the direction, amplitude, and polarization of the sound wave is found. The conditions for drift of a stripe domain structure are determined.

New brane solutions in higher-order gravity

We consider the higher-order gravity with dilaton and with the leading string theory corrections taken into account. The domain wall type solutions are investigated for arbitrary number of space–time dimensions. The explicit formulae for the fixed points and asymptotic behavior of generic solutions are given. We analyze and classify solutions with finite effective gravitational constant. There is a class of such solutions which have no singularities. We discuss in detail the relation between fine tuning and self-tuning and clarify in which sense our solutions are fine-tuning-free. The stability of such solutions is also discussed.