Domain Wall Arrays Research Articles

Co‐Polarized Second Harmonic Generation Induced by Ferroelectric Domains and Domain Wall Arrays (Advanced Optical Materials 21/2022)

Co‐Polarized Second Harmonic Generation Induced by Ferroelectric Domains and Domain Wall Arrays (Advanced Optical Materials 21/2022)

Co‐Polarized Second Harmonic Generation Induced by Ferroelectric Domains and Domain Wall Arrays

AbstractOptical second harmonic generation (SHG) is a sensitive and powerful technique to probe various symmetry breaking, especially ferroelectric/magnetic domains, in artificial thin films or heterostructures. In a wide range of ferroelectric crystals, a non‐trivial broken symmetry will emerge at domain boundaries, however, the contribution of such symmetry breaking to SHG is often neglected due to its random orientation. Here, a co‐polarized SHG effect from the well‐aligned domain wall arrays is observed in BiFeO3 thin films. This SHG component is highly dependent on the local orientation of the wall arrays, and its polarization feature reveals the Néel‐like evolution of electric polar vectors in the wall region. Based on this intriguing effect, mixed‐phase patches with four possible orientations in the quasi‐tetragonal stripes are identified by polarization‐sensitive SHG mapping. These findings not only clarify a critical SHG contribution in this multiferroic material, but also demonstrate an optical approach for exploring phase‐determined function unit.

Discrete energy spectrum of nonlinear spin ensembles in the ferrimagnet K0.4[Cr(CN)6][Mn(R/S)-pn](R/S)-pnH0.6

Series of spontaneous magnetization jumps have been observed on the background of a continuous relaxation of the magnetic moment of a molecular ferrimagnet in a constant magnetic field. A statistical analysis of the set of data has demonstrated the presence of at least two modes in the distribution of magnetization reversal jumps over their amplitude. It has been found that the number of modes in the distribution depends on the magnetic field and temperature and characterizes a discrete energy spectrum of nonlinear spin ensembles formed at low temperatures. The continuous component of the magnetic relaxation corresponds to the motion of domain-wall arrays in the temperature range from 20 to 50 K and to relaxation processes in the spin-soliton lattice at temperatures ranging from 2 to 10 K.

Operando x-ray photoelectron emission microscopy for studying forward and reverse biased silicon p-n junctions.

Significant progress in the understanding of surfaces and interfaces of materials for new technologies requires operando studies, i.e., measurement of chemical, electronic, and magnetic properties under external stimulus (such as mechanical strain, optical illumination, or electric fields) applied in situ in order to approach real operating conditions. Electron microscopy attracts much interest, thanks to its ability to determine semiconductor doping at various scales in devices. Spectroscopic photoelectron emission microscopy (PEEM) is particularly powerful since it combines high spatial and energy resolution, allowing a comprehensive analysis of local work function, chemistry, and electronic structure using secondary, core level, and valence band electrons, respectively. Here we present the first operando spectroscopic PEEM study of a planar Si p-n junction under forward and reverse bias. The method can be used to characterize a vast range of materials at near device scales such as resistive oxides, conducting bridge memories and domain wall arrays in ferroelectrics photovoltaic devices.

Domain wall arrays, fronts, and bright and dark solitons in a generalized derivative nonlinear Schrödinger equation

We obtain some exact solutions of a generalized derivative nonlinear Schrödinger equation, including domain wall arrays (periodic solutions in terms of elliptic functions), fronts, and bright and dark solitons. In certain parameter domains, fundamental bright and dark solitons are chiral, and the propagation direction is determined by the sign of the self-steepening parameter. Moreover, we also find the chirping reversal phenomena of fronts, and bright and dark solitons, and discuss two different ways to produce the chirping reversal.

Chirped Domain Wall Arrays and Solitary Waves in a Generalized Nonlinear Schrödinger Equation

We study a generalized nonlinear Schrödinger equation, and obtain some exact solutions, including domain wall arrays (periodic solutions in terms of elliptic functions), fronts, bright and dark solitons. In certain parameter domains, fundamental bright and dark solitons show directionality and hence are chiral, and the propagation direction is determined by the sign of the self-steepening parameter. Moreover, the chirping reversal phenomena of bright and dark solitons are found.

Domain wall and periodic solutions of a coupled ϕ6 model

Coupled triple well (ϕ6) one-dimensional potentials occur in both condensed matter physics and field theory. Here we provide a set of exact periodic solutions in terms of elliptic functions (domain wall arrays) and obtain single domain wall solutions in specific limits. Topological, nontopological (e.g., some pulselike solutions), as well as mixed domain walls are obtained. We relate these solutions to structural phase transitions in materials with polarization, shuffle modes, and strain. We calculate the energy and the asymptotic interaction between solitons for various solutions.

Domain wall and periodic solutions of coupled asymmetric double well models

Coupled asymmetric double well (aϕ2−bϕ3+cϕ4) one-dimensional potentials arise in the context of first order phase transitions both in condensed matter physics and field theory. Here we provide an exhaustive set of exact periodic solutions of such a coupled asymmetric model in terms of elliptic functions (domain wall arrays) and obtain single domain wall solutions in specific limits. We also calculate the energy and interaction between solitons for various solutions. Both topological (kinklike at T=Tc) and nontopological (pulselike for T≠Tc) domain wall solutions are obtained. We relate some of these solutions to domain walls in hydrogen bonded materials and also in the field theory context. As a by-product, we also obtain a new one parameter family of kink solutions of the uncoupled asymmetric double well model.

Angular Dependence of Domain Wall Resistivity in Artificial Magnetic Domain Structures

We exploit the ability to precisely control the magnetic domain structure of perpendicularly magnetized Pt/Co/Pt trilayers to fabricate artificial domain wall arrays and study their transport properties. The scaling behavior of this model system confirms the intrinsic domain wall origin of the magnetoresistance, and systematic studies using domains patterned at various angles to the current flow are excellently described by an angular-dependent resistivity tensor containing perpendicular and parallel domain wall resistivities. We find that the latter are fully consistent with Levy-Zhang theory, which allows us to estimate the ratio of minority to majority spin carrier resistivities, rho downward arrow/rho upward arrow approximately 5.5, in good agreement with thin film band structure calculations.

Domain wall and periodic solutions of coupled ϕ4 models in an external field

Coupled double well (ϕ4) one-dimensional potentials abound in both condensed matter physics and field theory. Here we provide an exhaustive set of exact periodic solutions of a coupled ϕ4 model in an external field in terms of elliptic functions (domain wall arrays) and obtain single domain wall solutions in specific limits. We also calculate the energy and interaction between solitons for various solutions. Both topological and nontopological (e.g., some pulse-like solutions in the presence of a conjugate field) domain walls are obtained. We relate some of these solutions to the recently observed magnetic domain walls in certain multiferroic materials and also in the field theory context wherever possible. Discrete analogs of these coupled models, relevant for structural transitions on a lattice, are also considered.

Quantum phase transition of striped domain walls

Quantum melting of two-dimensional (2D) striped domain wall arrays are investigated at zero temperature. It is revealed that the stripes with short-range interactions melt and become a stripe liquid in low density due to dislocations created by quantum fluctuation. This quantum melting transition is of second order and in the 3D XY universality class. Quantum melting in the presence of long-range interactions that fall off as power laws is also studied. This result is applied to incommensurate domain walls in 2D adsorbed atoms on substrate and doped antiferromagnets.

Direct excitation of standing-wave vibrations of domain walls

We propose a method of parametrically exciting natural vibrations of magnetic 180° domain-wall arrays without involving an intermediate pump mode. The rf field is applied along the hard direction parallel to the wall plane. The derived excitation threshold amounts to several oersted for typical low-loss garnet films.