scholarly journals Direct observation of Σ7 domain boundary core structure in magnetic skyrmion lattice

2016 ◽  
Vol 2 (2) ◽  
pp. e1501280 ◽  
Author(s):  
Takao Matsumoto ◽  
Yeong-Gi So ◽  
Yuji Kohno ◽  
Hidetaka Sawada ◽  
Yuichi Ikuhara ◽  
...  
Keyword(s):  
Dynamic Properties ◽  
Domain Boundary ◽  
Coincidence Site Lattice ◽  
Core Structure ◽  
Relaxation Mode ◽  
Structure Relaxation ◽  
Hexagonal Close Packed ◽  
Domain Boundaries ◽  
Magnetic Skyrmions ◽  
Boundary Core

Skyrmions are topologically protected nanoscale magnetic spin entities in helical magnets. They behave like particles and tend to form hexagonal close-packed lattices, like atoms, as their stable structure. Domain boundaries in skyrmion lattices are considered to be important as they affect the dynamic properties of magnetic skyrmions. However, little is known about the fine structure of such skyrmion domain boundaries. We use differential phase contrast scanning transmission electron microscopy to directly visualize skyrmion domain boundaries in FeGe1−xSix induced by the influence of an “edge” of a crystal grain. Similar to hexagonal close-packed atomic lattices, we find the formation of skyrmion “Σ7” domain boundary, whose orientation relationship is predicted by the coincidence site lattice theory to be geometrically stable. On the contrary, the skyrmion domain boundary core structure shows a very different structure relaxation mode. Individual skyrmions can flexibly change their size and shape to accommodate local coordination changes and free volumes formed at the domain boundary cores. Although atomic rearrangement is a common structural relaxation mode in crystalline grain boundaries, skyrmions show very unique and thus different responses to such local lattice disorders.

Influence of Micropipe and Domain Boundary in SiC Substrate on the DC Characteristics of AlGaN/GaN HFET

2007 ◽  
Vol 556-557 ◽  
pp. 1043-1046 ◽  
Author(s):  
Hiroyuki Sazawa ◽  
Tomohisa Kato ◽  
Kazutoshi Kojima ◽  
K. Furuta ◽  
K. Hirata ◽  
...  
Keyword(s):  
Domain Boundary ◽  
Topographic Analysis ◽  
Raman Analysis ◽  
X Ray ◽  
Free Carriers ◽  
Crystal Imperfections ◽  
Dc Characteristics ◽  
Domain Boundaries ◽  
Gan Hfet ◽  
Gan Crystal

AlGaN/GaN HFETs were fabricated around micropipes and on a domain boundary in a semi-insulating silicon carbide (SI-SiC) substrate and the DC characteristics of the fabricated devices were measured. Devices around micropipe showed no pinch-off or large gate leakage. The devices on the domain boundaries showed no degradation in the performances, even though an X-ray topographic analysis indicated that crystal imperfections, due to the defects, propagated to the GaN layer across the hetero interface. Based on these results, we concluded that micropipe degrades the DC characteristics and that the domain boundary does not affect the DC characteristics. From Raman analysis on the devices around the micropipes, these degradations could be attributed to the free carriers introduced into the GaN crystal by the micropipes.

A Study Of Domain Boundary Structures In Lead Titanate Single Crystals

1991 ◽  
Vol 238 ◽  
Author(s):  
C. C. Chou ◽  
J. Li ◽  
C. M. Wayman
Keyword(s):  
Electron Microscopy ◽  
Single Crystals ◽  
Lead Titanate ◽  
Mixed Type ◽  
Domain Boundary ◽  
Dynamical Theory ◽  
Fringe Contrast ◽  
Transmission Electron ◽  
Domain Boundaries ◽  
Contrast Analysis

ABSTRACTDomain boundary structures of flux-grown poly-domain lead titanate single crystals have been studied using transmission electron microscopy. 90° and 180° domain boundaries were seen in the crystals and were systematically analyzed under various diffraction conditions. Although 90° domain boundaries are supposely δ-type boundaries in BaTiO3, our results show that displacement plays an important role at boundaries and the extreme fringe contrast (EFC) behavior of 90° boundaries is of the mixed type. In the present work, an analysis based upon the two beam dynamical theory was conducted and a rule similar to stacking-fault contrast analysis was established to predict the geometric configuration of a 180° domain boundary using EFC behavior. Examples are given and verified by tilting experiments and electron diffraction. The results are consistent and offer a convenient way to distinguish between 90° and 180° boundaries.

Determination of displacement vector on 180° domain boundary and polarization arrangements in lead titanate crystals

1997 ◽  
Vol 12 (2) ◽  
pp. 457-466 ◽  
Author(s):  
Chen-Chia Chou ◽  
C. Marvin Wayman
Keyword(s):  
Lead Titanate ◽  
Displacement Vector ◽  
Domain Boundary ◽  
Polarization Vector ◽  
Dynamical Theory ◽  
Fringe Contrast ◽  
Displacement Vectors ◽  
Domain Boundaries ◽  
Contrast Analysis ◽  
Diffraction Patterns

180° domain boundaries in flux-grown lead titanate single crystals show intriguing domain boundary extreme fringe contrast using transmission electron microscopy. Symmetrically distributed domain boundaries with alternate contrast have been observed, indicating that opposite displacement vectors exist one by one at boundaries. If appropriate reflection vectors were employed, an inclined domain boundary shows reversed fringe contrast. An analysis based upon the two-beam dynamical theory and a rule similar to stacking-fault contrast analysis was employed to predict the geometric configuration of a 180° domain boundary using the extreme fringe contrast (EFC) behavior. Appropriately choosing reflection vectors and utilizing the EFC reversal, a displacement vector as well as the polarization vector arrangement across a 180° domain boundary can be unambiguously identified. Employing the information derived from diffraction patterns and a tilting experiment across a nearby 90° boundary, the whole polarization configuration can be uniquely determined.

STUDY ON THE PEIREL–NABARRO STRESS OF IRON ALUMINIDES

2012 ◽  
Vol 19 (06) ◽  
pp. 1250057 ◽  
Author(s):  
L. X. PANG ◽  
N. F. HAN ◽  
H. SHI ◽  
J. XU ◽  
X. H. HAO ◽  
...  
Keyword(s):  
Domain Boundary ◽  
Antiphase Domain ◽  
Iron Aluminides ◽  
Stress Model ◽  
Theoretical Yield ◽  
Domain Boundaries ◽  
Ordered Intermetallic ◽  
Critical Resolved Shear Stress ◽  
B2 Structure ◽  
Type Crystal

The modified Peirel–Nabarro model of dislocations is not valid for the superdislocation bounded by the antiphase domain boundaries in long-range ordered intermetallic. In this work, a new Peirel–Nabarro Stress model is developed to take into account the critical resolved shear stress of antiphase domain boundary (APDB). Based on it, the Peirel–Nabarro Stress of DO3 structure and B2 structure in iron aluminides are calculated. Comparing the Peirel–Nabarro Stress of dislocations and the crystal theoretical yield strength, the results demonstrate B2-type crystal has good plasticity. It coincides with the experimental results well.

Enhanced Light Emission at Self-assembled GaN Inversion Domain Boundary

2011 ◽  
Vol 1324 ◽  
Author(s):  
Mei-Chun Liu ◽  
Yuh-Jen Cheng ◽  
Jet-Rung Chang ◽  
Chun-Yen Chang
Keyword(s):  
Molecular Beam ◽  
Light Emission ◽  
Domain Boundary ◽  
Mbe Growth ◽  
Polarity Inversion ◽  
Circular Pattern ◽  
Inversion Domain ◽  
Domain Boundaries ◽  
Self Assembled ◽  
Inversion Domain Boundaries

ABSTRACTWe report the fabrication of GaN lateral polarity inversion heterostructure with self assembled crystalline inversion domain boundaries (IDBs). The sample was fabricated by two step molecular-beam epitaxy (MBE) with microlithography patterning in between to define IDBs. Despite the use of circular pattern, hexagonal crystalline IDBs were self assembled from the circular pattern during the second MBE growth. Both cathodoluminescent (CL) and photoluminescent (PL) measurements show a significant enhanced emission at IDBs and in particular at hexagonal corners. The ability to fabricate self assembled crystalline IDBs and its enhanced emission property can be useful in optoelectronic applications.

Microdiffraction from out of Phase Domain Boundaries and Stacking Faults

1982 ◽  
Vol 40 ◽  
pp. 698-699
Author(s):  
J. Zhu ◽  
J.M. Cowley ◽  
H.Q. Ye
Keyword(s):  
Electron Beam ◽  
Source Function ◽  
Domain Boundary ◽  
Antiphase Domain ◽  
Step Function ◽  
Phase Object ◽  
Phase Domain ◽  
Domain Boundaries ◽  
The Fourier Transform ◽  
Coherent Source

It has been pointed out1 that any discontinuity at the edge of a crystal or within a crystal may give rise to spot splitting in microdiffraction patterns.The present work gives the basic theory for an antiphase domain boundary in Cu3Au and a twinning boundary in a f.c.c. crystal illuminated by a finite electron beam, which has a diameter of about 15Å. The treatment is based on the weak phase object approximation. These boundaries are planar faults. Multiplying a step function s(x) by the crystal potential expresses the discontinuity in the potential of the sample. When both sides of the boundary in the sample are illuminated by the finite coherent source and the boundary is parallel to the electron beam, the splitting of microdiffraction spots results from the convolution of the Fourier transform of the step function and the finite coherent source function.

scholarly journals Dielectric Response and Structural Analysis of (A3+, Nb5+) Cosubstituted CaCu3Ti4O12 Ceramics (A: Al and Bi)

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5822
Author(s):  
Hicham Mahfoz Kotb ◽  
Mohamad M. Ahmad ◽  
Adil Alshoaibi ◽  
Koji Yamada
Keyword(s):  
Grain Boundary ◽  
Relative Permittivity ◽  
Domain Boundary ◽  
Secondary Phase ◽  
High Energy ◽  
Relaxation Processes ◽  
Heterogeneous Structure ◽  
Reactive Sintering ◽  
Domain Boundaries ◽  
A Minor

CaCu3Ti4-x((A0.05Nb0.05))xO12 ceramics (A: Al and Bi; x = 0, 0.3) were synthesized by high-energy mechanical ball milling and reactive sintering at 1050 °C in air. Rietveld refinement of XRD data revealed the pure and (Al3+, Nb5+) cosubstituted ceramics contained a minor CuO secondary phase with a mole fraction of about 3.2% and 6.9%, respectively, along with a CaCu3Ti4O12 (CCTO)-like cubic structure. In addition, (Bi3+, Nb5+) cosubstituted ceramics had a pyrochlore (Ca2(Ti, Nb)2O7) secondary phase of about 18%. While the (Al3+, Nb5+) cosubstituted CCTO showed the highest relative permittivity (ε’ = 3.9 × 104), pure CCTO showed the lowest dielectric loss (tanδ = 0.023) at 1 kHz and 300 K. Impedance-spectroscopy (IS) measurements showed an electrically heterogeneous structure for the studied ceramics, where a semiconducting grain was surrounded by highly resistive grain boundary. The giant relative permittivity of the ceramics was attributed to the Maxwell–Wagner polarization effect at the blocking grain boundaries and domain boundaries. The higher tanδ of the cosubstituted samples was correlated with their lower grain boundary’s resistivity, as confirmed by IS analysis. Modulus-spectrum analysis revealed two relaxation processes for the pure and (Bi3+, Nb5+) cosubstituted CCTO samples. Dissimilar behavior was observed for the (Al3+, Nb5+) cosubstituted CCTO, where three relaxation mechanisms were observed and attributed to the grain, domain-boundary, and grain-boundary responses.

scholarly journals preciseTAD: A machine learning framework for precise 3D domain boundary prediction at base-level resolution

2020 ◽  
Author(s):  
Spiro C. Stilianoudakis ◽  
Mikhail G. Dozmorov
Keyword(s):  
Domain Boundary ◽  
Model Performance ◽  
Learning Framework ◽  
Base Level ◽  
Topologically Associating Domains ◽  
Annotation Data ◽  
Domain Boundaries ◽  
Under Sampling ◽  
Domain Boundary Prediction ◽  
Genome Annotations

AbstractThe low resolution of high-throughput chromatin conformation capture data limits the precise mapping of boundaries of topologically associating domains and chromatin loops. We developed preciseTAD, an optimized random forest model trained on high-resolution genome annotation data (e.g., CTCF ChIP-seq) to predict the location of domain boundaries at base-level resolution. Distance between boundaries and annotations, random under-sampling, and transcription factor binding sites resulted in best model performance. preciseTAD boundaries were more enriched for CTCF, RAD21, SMC3, and ZNF143, and conserved across cell lines. Using genome annotations, pre-trained models can detect boundaries in cells without Hi-C data. preciseTAD is available at https://bioconductor.org/packages/preciseTAD

Topological spin/structure couplings in layered chiral magnet Cr1/3TaS2: The discovery of spiral magnetic superstructure

2021 ◽  
Vol 118 (40) ◽  
pp. e2023337118
Author(s):  
Kai Du ◽  
Fei-Ting Huang ◽  
Jaewook Kim ◽  
Seong Joon Lim ◽  
Kasun Gamage ◽  
...  
Keyword(s):  
Domain Walls ◽  
Topological Defects ◽  
Magnetic Texture ◽  
Spintronic Devices ◽  
Wide Range ◽  
Domain Boundaries ◽  
Complex Spin ◽  
Magnetic Skyrmions ◽  
Magnetic States ◽  
Opposite Chirality

Chiral magnets have recently emerged as hosts for topological spin textures and related transport phenomena, which can find use in next-generation spintronic devices. The coupling between structural chirality and noncollinear magnetism is crucial for the stabilization of complex spin structures such as magnetic skyrmions. Most studies have been focused on the physical properties in homochiral states favored by crystal growth and the absence of long-ranged interactions between domains of opposite chirality. Therefore, effects of the high density of chiral domains and domain boundaries on magnetic states have been rarely explored so far. Herein, we report layered heterochiral Cr1/3TaS2, exhibiting numerous chiral domains forming topological defects and a nanometer-scale helimagnetic order interlocked with the structural chirality. Tuning the chiral domain density, we discovered a macroscopic topological magnetic texture inside each chiral domain that has an appearance of a spiral magnetic superstructure composed of quasiperiodic Néel domain walls. The spirality of this object can have either sign and is decoupled from the structural chirality. In weak, in-plane magnetic fields, it transforms into a nonspiral array of concentric ring domains. Numerical simulations suggest that this magnetic superstructure is stabilized by strains in the heterochiral state favoring noncollinear spins. Our results unveil topological structure/spin couplings in a wide range of different length scales and highly tunable spin textures in heterochiral magnets.

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