Changes In Domain Structure Research Articles

Interlayer coupling in symmetric and asymmetric CoFeB based trilayer films with different domain structures: Role of spacer layer and temperature

We report the study of interlayer coupling between Co20Fe60B20 (CoFeB262) layers and the resulting magnetic properties of trilayer [CoFeB262 (y nm)/Cr (x nm)/CoFeB262 (20 nm)] films with symmetric (y = 20) and asymmetric (y = 100) structures. All as-deposited CoFeB262 films exhibit amorphous structure. Surface topography studies display clear and uniform surfaces with very fine and sparsely dispersed nanosized grains. The average surface roughness of the CoFeB262 films increases marginally as y is increased from 20 to 100 nm. The shape of magnetic hysteresis (M-H) loop of single-layer CoFeB262 (y nm) films transforms from rectangular shape for CoFeB262 (20 nm) film to transcritical one for CoFeB262 (100 nm) film. This is mainly due to change in magnetic domain structure from in-plane magnetization to dense stripe domain with increase in y. On the other hand, the shape of the M-H loops in trilayer films strongly depends on x, y and temperature. All symmetric trilayer films show single magnetization reversal process at room temperature with a kink in the first quadrant for films with x < 1. Coercivity (HC), saturation field (Hsat) and remanence ratio (MR/MS) show oscillatory behaviors as a function of x. For asymmetric films, the transcritical loop changes into rectangular one after the introduction of Cr interlayer. This also causes a large reduction in Hsat and enhances MR/MS sharply. Temperature dependent M-H loops at low temperatures reveal the disappearance of the kink in symmetric trilayer films and the formation of additional steps in asymmetric trilayer films with x > 0.5. The relative increase in HC with decreasing temperature is found to be larger for symmetric films as compared to asymmetric ones. The observed results are explained on the basis of change in the interlayer coupling between CoFeB262 layers with change in x, y and temperature dependent interfacial strain, which modifies the nature of interlayer coupling. These results also demonstrate that dense stripe domain of thicker CoFeB262 layers can be easily converted into simple in-plane magnetization using trilayer thin films.

The impact of bending stress on magnetic properties of Finemet type microwires and ribbons

In our research we studied the influence of bending on the total magnetic losses, the coercivity of minor hysteresis loops and the virgin magnetization curves of amorphous ribbons and microwires prepared from Finemet-type alloy wound on a mandrel of different diameters. The impact of various factors contributing on static and dynamic magnetic properties through bending stress are discussed. The factors pertain to contribution of the magnetoelastic anisotropy, the onset of the strain-induced magnetization, the changes of domain structure and the mobility of domain walls. The major contribution of hysteresis losses as-compared to the eddy-current losses have been observed on changing the mandrel diameter in wound ribbons and wires. The total specific losses of the Finemet-type ribbons are lower than that of microwires at the frequencies ranging from 50 to 400 Hz. Observed difference in the magnetic properties is attributed to different magnetization processes of amorphous microwires and ribbons. A different geometry and magnetoelastic anisotropy of studied materials are most likely to influence the formation of different domain structures.

Effect of cooling rate on magnetic domain structure and magnetic properties of Tb0.27Dy0.73Fe1.95 alloys solidified in high magnetic field

In this work, Tb0.27Dy0.73Fe1.95 alloys were solidified in a high magnetic field of 4.4 T at various cooling rates. Changes in the magnetostriction, crystal orientation, magnetization, and magnetic domain of the solidified alloys were investigated. The application of the magnetic field can induce &amp;lt;111&amp;gt; orientation of (Tb, Dy)Fe2 phase. However, the effect of the magnetic field is strongly dependent on the cooling rate. The alloy solidified at 5 °C/min shows the highest magnetostriction, strongest &amp;lt;111&amp;gt; orientation, best contrast of light and dark in the domain image, and fastest magnetization, and followed in descending order by the alloys solidified at 1.5 °C/min and 60 °C/min. The change in the magnetostriction of the alloys can be attributed to the changes in crystal orientation and magnetic domain structure caused by both the magnetic field and cooling rate.

Thickness Dependent Surface Topography, Magnetic Properties and Magnetic Domain Structure of Amorphous FeTaC Thin Films

We report systematic investigation of thickness dependent surface topography, magnetic properties and magnetic domain structures of amorphous Fe80Ta8C12 (x nm) films with x=5–100 nm. All the as-deposited films fabricated directly on thermally oxidized Si substrate at ambient temperature using magnetron sputtering technique exhibit amorphous structure. The structural studies reveal that island-like structure in ultra-thin films transforms into continuous one with increasing x>10. In addition, the average surface roughness increases with increasing x, but without any systematic dependency on x. Room temperature magnetic properties illustrate that the paramagnetic nature observed for films with x 97%), low coercivity (HC 3.5 kA/m) and HS (>40 kA/m) and reduced MR/MS (<45%). The magnetic domain studies not only reveal that the domains change from in-plane magnetization to dense stripe domain pattern with increasing x due to enhancement of effective magnetic anisotropy caused by stress quenched in during deposition, but also confirm that films with 12<x<40 exhibit in-plane magnetization with uniaxial anisotropy. High temperature thermomagnetization reveal a clear magnetic phase transition from ferromagnetic to paramagnetic state at relatively higher temperature of about 530 K. The observed results are elucidated on the basis of enhanced effective magnetic anisotropy, change in the magnetic domain structure and magnetic disorder with increasing FeTaC film thickness.

Magnetic Domain Patterns in Bilayered Ribbons Studied by Magnetic Force Microscopy and Magneto-Optical Kerr Microscopy.

The magnetic domain patterns of amorphous bilayered FeSiB/FeNbSiB and FeNbCuSiB/CoSiB ribbons are observed and analysed using the magneto-optical Kerr microscopy (MOKM) and magnetic force microscopy (MFM). Both microscopic techniques are highly sensitive to the sample surface; possibility of Kerr microscopy to visualize the domains separately in both layers is achieved by focusing the laser spot on the ribbon cross section. Wide curved domains as well as fine fingerprint domains were detected at the surface of ribbons due to presence of local stresses coming from the preparation process. With respect to high lateral resolution of MFM and its out-of-plane magnetization sensitivity, the perpendicularly magnetized crossed stripe domain patterns can be selected as well. Coiling of the ribbons on the half-round-end sample holder is often used to induce and control the magnetic anisotropy of these alloys. Changes in the magnetic domain structure at the outer-coiled surface and its dependence on the sign of magnetostriction coefficient are discussed in detail. Finally, the MFM images in the presence of external in-plane magnetic field up to ±40 kA/m are shown.

The change of domain structure of the amorphous microwire of Fe73.5Cu1Nb3Si13.5B9 composition under thermal treatment

The investigation on domain structure evolution under variation of magnetostriction, phase composition and internal stresses was provided. Glass-coated amorphous microwires of Fe73.5Cu1Nb3Si13.5B9 composition with positive magnetostriction were studied. The decrease of internal stresses and controlled crystallization leading to changes in the phase composition and reduction of magnetostriction were observed under different thermal treatment. The domain structure of the as-prepared and annealed microwires was studied by the method of magneto-optical indicator films. The estimation of the domain size was realized by Fourier transform from the domain contrast of magneto-optical images. The regularities of the influence of thermal treatment on the magnetic domain structure of microwires have been estimated.

Change in Magnetic Domain Structure of Nd‐Fe‐B Sintered Magnets by Compressive Stress

SUMMARYTo clarify the relationship between compressive stresses and demagnetization of Nd‐Fe‐B sintered magnets, we have examined the change in domain configuration by compressive stresses using a Kerr microscope. The magnetic domains of five kinds of Nd‐Fe‐B sintered magnets have been observed. The magnets have a coercivity of 0.8 MA/m to 1.4 MA/m and residual magnetic flux density of 1.3 T to 1.5 T. Irreversible demagnetization of Nd‐Fe‐B magnets with a low coercivity of 0.875 MA/m and high residual magnetic flux density of 1.41 T to 1.47 T have occurred from applying a compressive stress of 100 MPa. The compression‐affected area is approximately 0.14%. The stress more than 50 MPa is needed to demagnetize Nd‐Fe‐B magnets. The amount of irreversible demagnetization depends upon the intensity of the compressive stress as well as the residual magnetic flux and coercive force of the magnets.

Dielectric nonlinear behavior of (Ba0.95Ca0.05)(Ti0.83Zr0.17)O3‐based multi‐layer ceramic capacitor

AbstractThe influence of temperature on the variation in dielectric nonlinearity and domain structures was investigated for the (Ba0.95Ca0.05)(Ti0.83Zr0.17)O3 (BCTZ)‐based multilayer ceramic capacitor that shows a diffuse phase transition. Whereas the dielectric constant (εr) vs temperature shows a broadened maximum peak at low ac driving field, such a peaked behavior disappears at high ac driving field due to an abrupt increase in dielectric constants at low temperatures. Such low temperature effect can be associated with an enhanced spontaneous polarization (PS) and a significant increase in irreversible domain wall contribution to polarization representing normal ferroelectric behavior based on the Preisach analysis. No ferroelectric domain contrasts were observed at room temperature through transmission electron microscopy. However, they appeared and became more and more distinct with the decrease in temperature, and the crystal structure also changed from cubic to rhombohedral with increased lattice constants. It demonstrates that the dramatic increase in the dielectric nonlinearity with decreasing temperatures originates from the corresponding changes in domain and crystal structure, where the polar‐micro‐regions of BCTZ at room temperature change to normal ferroelectric domains at low temperatures.

Change of magnetic domain structure by mechanically induced twin boundary motion in Ni-Mn-Ga single crystal

The single variant state exhibits usual labyrinth and band magnetic domains depending on orientation of easy magnetization axis. By the passage of single twin boundary induced by mechanical stress the rake and granular domain patterns are formed. These domain patterns are further modified by repeated passage of the twin boundary resulting in similar domain patterns in the sample even though the orientation of the magnetization is different.

Temperature‐ and E‐field‐dependent domain configuration and electrical properties in (K, Na, Li)(Nb, Ta, Sb)O3 single crystal

AbstractE‐field‐ and temperature‐dependent domain evolution of lead‐free tetragonal (K, Na, Li)(Nb, Sb, Ta)O3 (KNLNTS) single crystals as well as its corresponding electrical properties have been investigated. When E field is applied along [011]C direction, (2T) engineered domain structure is formed. Spontaneous polarizations switch under a critical electric field (around 4‐5 kV/cm), resulting in significant changes in domain structure and great improvement in piezoelectric properties. Furthermore, it is found that piezoelectric constant d31 and electromechanical coupling factor k31 of [011]C poled KNLNTS single crystal decrease with temperature. The extrinsic and intrinsic piezoelectric responses are discussed from the viewpoint of domain structure and lattice distortion, respectively. Our results show that the nanodomain structure relaxes and the lattice distortion declines with temperature, resulting in reduction of extrinsic and intrinsic piezoelectric responses, respectively. Therefore, the piezoelectric instability is ascribed to the decrease of both extrinsic and intrinsic contributions. This work provides a better understanding of domain engineering technique, and the useful information on the improvement of both piezoelectricity and temperature stability of the lead‐free piezoelectric materials.

Fe on W(001) from continuous films to nanoparticles: Growth and magnetic domain structure

The evolution of the structural and magnetic properties of Fe films during growth on the W(001) surface have been studied with low energy electron diffraction, real-time low energy electron microscopy, and quasi-real-time, spin-polarized low energy electron microscopy in the absence of a magnetic field (virgin state). Depending on the growth temperature, different growth modes are observed: growth of atomically rough and highly strained (10.4% tensile) pseudomorphic films at room temperature, kinetically limited layer-by-layer growth (quasi--Frank-van der Merwe growth mode) of smooth pseudomorphic films up to 4 monolayers at around 500 K and growth of fully relaxed three-dimensional Fe islands on top of a thermodynamically stable 2-monolayer-thick wetting layer (Stranski-Krastanov growth mode) at and above 700 K. Around 500 K, layered growth is terminated by partial (2 monolayers) dewetting of the metastable Fe film and formation of thin, partially relaxed, elongated islands on a thermodynamically stable 2 monolayer film. Ferromagnetic order is first detected during growth at room temperature at 2.35 monolayer Fe film thickness. The magnetization is in-plane with a thickness-dependent direction, rotating from the substrate $\ensuremath{\langle}110\ensuremath{\rangle}$ directions at 3 monolayers toward the $\ensuremath{\langle}100\ensuremath{\rangle}$ directions at 4 monolayers and back again toward the $\ensuremath{\langle}110\ensuremath{\rangle}$ directions at about 8 monolayers. The in-plane spin reorientation that occurs at room temperature is accompanied by significant changes of the magnetic domain structure. In the Frank-van der Merwe growth regime, large magnetic domains are observed in metastable 3 and 4 monolayer films. The isolated three-dimensional Fe islands that form in the Stranski-Krastanov regime have vortex, quasi-single domain ($C$ state), or single magnetic domain structures, depending on their size and shape. The detailed results that are obtained with high thickness, lateral and azimuthal angular resolution with spin-polarized low energy electron microscopy are compared with earlier laterally averaging and laterally resolving magnetic studies, and discrepancies are explained.

Mechanical stress-induced switching kinetics of ferroelectric thin films at the nanoscale

We investigate ferroelectric domain structure and piezoelectric response under variable mechanical compressive stress in Pb(Zr0.2TiO0.8)O3 (PZT) thin films using high-resolution piezoresponse force microscopy (PFM) and an in situ sample bending stage. Measurements reveal a drastic change in the ferroelectric domain structure which is presented along with details of the mediating switching process involving domain wall motion, nucleation, and domain wall roughening under an applied external mechanical stimulus. Furthermore, local PFM hysteresis loops reveal significant changes in the observed coercive biases under applied stress. The PFM hysteresis loops become strongly imprinted under increasing applied compressive stress.

Shedding light on the expansion and diversification of the Cdc48 protein family during the rise of the eukaryotic cell.

BackgroundA defining feature of eukaryotic cells is the presence of various distinct membrane-bound compartments with different metabolic roles. Material exchange between most compartments occurs via a sophisticated vesicle trafficking system. This intricate cellular architecture of eukaryotes appears to have emerged suddenly, about 2 billion years ago, from much less complex ancestors. How the eukaryotic cell acquired its internal complexity is poorly understood, partly because no prokaryotic precursors have been found for many key factors involved in compartmentalization. One exception is the Cdc48 protein family, which consists of several distinct classical ATPases associated with various cellular activities (AAA+) proteins with two consecutive AAA domains.ResultsHere, we have classified the Cdc48 family through iterative use of hidden Markov models and tree building. We found only one type, Cdc48, in prokaryotes, although a set of eight diverged members that function at distinct subcellular compartments were retrieved from eukaryotes and were probably present in the last eukaryotic common ancestor (LECA). Pronounced changes in sequence and domain structure during the radiation into the LECA set are delineated. Moreover, our analysis brings to light lineage-specific losses and duplications that often reflect important biological changes. Remarkably, we also found evidence for internal duplications within the LECA set that probably occurred during the rise of the eukaryotic cell.ConclusionsOur analysis corroborates the idea that the diversification of the Cdc48 family is closely intertwined with the development of the compartments of the eukaryotic cell.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0790-1) contains supplementary material, which is available to authorized users.

Effects of composition, thickness and temperature on the magnetic properties of amorphous CoFeB thin films

We report composition, thickness and temperature dependent magnetic properties of amorphous Co80-yFeyB20 (x nm) films with y = 40,60 and x = 7–200 nm prepared directly on thermally oxidized Si substrate using magnetron sputtering technique. All the as-deposited films exhibit amorphous structure. For both the compositions, the shape of magnetic hysteresis (M-H) loops strongly depends on their thicknesses, i.e., the films with x ≤ 20 exhibit either rectangular shape or flat type loops, which change into transcritical type beyond a critical thickness (x > 50). Room temperature coercivity (HC) and field required for saturation (HS) increase almost linearly with increasing x between 7 and 20, but exhibit a rapid increase for the films with x up to 100 and then decrease slightly for x = 200 film. Thickness dependence of HC and HS varies also with composition. This is attributed to the development of effective magnetic anisotropy (Keff) with increasing film thickness, which causes a change in magnetic domain structure from in-plane magnetization to stripe domains and degrades the magnetic properties above critical thickness. Temperature dependent M-H loops reveal that the loop shapes do not change with temperature for a given film. However, the values of HC and HS increase with decreasing temperature and the rate of increase depends on the composition and thickness. Similarly, the variation of Keff with temperature also displays a considerable dependency on the composition. The observed results are discussed on the basis of development of compositional and thickness dependent effective magnetic anisotropy, which changes the magnetic domain structure with increasing CoFeB film thickness.

Effects of multi-stage aging on the microstructure, domain structure and magnetic properties of Fe-24Cr-12Co-1.5Si ribbon magnets

Fe-24Cr-12Co-1.5Si ribbons were prepared by melt spinning at a roller speed of 40 m/s, which were then treated by multi-stage aging between 647 °C and 540 °C. This article focuses on the microstructure and domain structure changes in the aging process by Lortenz transmission electron microscopy. It has been found that the phase change reaction of Cr(M) + α→α1+α2 occurs during aging. After that, the ribbons are composed of ferromagnetic α1 phase (about 92.4 vol%-98 vol%) and weakly magnetic α2 phase (about 7.6 vol%-2 vol%). These two phases form a uniform and periodical spinodal structure, characterized by maze magnetic domain structure. Two types of domain walls can be formed between adjacent α1 phases, one is 90° and the other is 180°. The pinning mechanism in which α2 phase works as the pinning center is the main magnetization mechanism of the ribbons, and magnetization process is carried out mainly through the rotation of magnetic moments. The coercivity as high as 742 Oe can be achieved in the ribbons even if they have not been heat treated in magnetic fields.

Domain imaging in ferroelectric thin films via channeling-contrast backscattered electron microscopy

Ferroelastic domain walls provide opportunities for deterministically controlling mechanical, optical, electrical, and thermal energy. Domain wall characterization in micro- and nanoscale systems, where their spacing may be of the order of 100 nm or less is presently limited to only a few techniques, such as piezoresponse force microscopy and transmission electron microscopy. These respective techniques cannot, however, independently characterize domain polarization orientation and domain wall motion in technologically relevant capacitor structures or in a non-destructive manner, thus presenting a limitation of their utility. In this work, we show how backscatter scanning electron microscopy utilizing channeling contrast yield can image the ferroelastic domain structure of ferroelectric films with domain wall spacing as narrow as 10 nm. Combined with electron backscatter diffraction to identify grain orientations, this technique provides information on domain orientation and domain wall type that cannot be readily measured using conventional non-destructive methods. In addition to grain orientation identification, this technique enables dynamic domain structure changes to be observed in functioning capacitors utilizing electrodes that are transparent to the high-energy backscattered electrons. This non-destructive, high-resolution domain imaging technique is applicable to a wide variety of ferroelectric thin films and a multitude of material systems where nanometer-scale crystallographic twin characterization is required.

Magnetic properties of single-layer and multilayer structured Co40Fe40B20 thin films

We report systematic investigations of thickness dependent magnetic properties of amorphous Co40Fe40B20 (x nm) single-layer films and effects of number of multilayers and thickness of spacer layer on the magnetic properties of multilayer structured [Co40Fe40B20 (y nm)/Ta (z nm)]n=1–3/Co40Fe40B20 (y nm) films prepared directly on thermally oxidized Si substrate using magnetron sputtering technique. All the as-deposited films at ambient temperature exhibit amorphous structure. For single-layer films, coercivity (HC) and field required for saturation (HS) increase gradually with increasing x from 10 to 30nm, but exhibit a rapid increase when x≥67nm. This behaviour was attributed to the change in the magnetic domain structure from in-plane magnetization to stripe domains caused by the development of effective magnetic anisotropy instigated by stress accumulated during the deposition. High temperature thermomagnetization data show the Curie temperature of Co40Fe40B20 (20nm) film as 512K. On the other hand, the introduction of thin Ta spacer layers in multilayer films helps reducing HC and HS substantially, but magnitude of the reduction depends strongly on the values of n and z. The increase of n diminishes the development of effective magnetic anisotropy in CoFeB film. This is due to the reduction in the thickness of the ferromagnetic layers, which changes the magnetic domain structure, and the optimum value of z enhancing interlayer coupling between CoFeB layers. Hence, the magnetic properties of the multilayer thin films are improved. The observed results are elucidated on the basis of change in the magnetic domain structure with increasing film thickness in single-layer films, and with increasing number of multilayers and spacer layer thickness dependent interlayer coupling in multilayer structured thin films.

Hydrostatic pressure effect on magnetic hysteresis parameters of pseudo‐single‐domain magnetite

AbstractThis paper reports the first in situ magnetic hysteresis measurements of pseudo‐single‐domain (PSD) magnetite under high pressure up to 1 GPa. The magnetic hysteresis measurements of stoichiometric PSD magnetite samples under hydrostatic pressure were carried out using a piston‐cylinder high‐pressure cell, and the pressure dependence of the hysteresis parameters of PSD magnetite was calculated from the hysteresis curves. It was found that coercivity (Bc) increases with increasing pressure as a quadratic function up to 1 GPa by ∼90%, which is different from the pressure dependences of Bc of multidomain and single‐domain magnetites. Coercivity of remanence also increases as a quadratic function, and saturation remanence (Mrs) increases with pressure up to 0.5 GPa by ∼20% until reaching saturation. In contrast, saturation magnetization is constant up to 1 GPa. The approximate demagnetizing factor calculated from the ratio Bc/Mrs increases with increasing pressure, suggesting that the number of lamellar domains increases with increasing pressure. The number of lamellar domains and domain wall width are theoretically estimated to increase under high pressure due to the changes in magnetostriction, elastic, and magnetocrystalline anisotropy constants, and these changes in magnetic domain structure should relate to the changes in the magnetic properties of PSD magnetite.

Three-dimensional disorganization of the cancer genome occurs coincident with long-range genetic and epigenetic alterations

A three-dimensional chromatin state underpins the structural and functional basis of the genome by bringing regulatory elements and genes into close spatial proximity to ensure proper, cell-type–specific gene expression profiles. Here, we performed Hi-C chromosome conformation capture sequencing to investigate how three-dimensional chromatin organization is disrupted in the context of copy-number variation, long-range epigenetic remodeling, and atypical gene expression programs in prostate cancer. We find that cancer cells retain the ability to segment their genomes into megabase-sized topologically associated domains (TADs); however, these domains are generally smaller due to establishment of additional domain boundaries. Interestingly, a large proportion of the new cancer-specific domain boundaries occur at regions that display copy-number variation. Notably, a common deletion on 17p13.1 in prostate cancer spanning the TP53 tumor suppressor locus results in bifurcation of a single TAD into two distinct smaller TADs. Change in domain structure is also accompanied by novel cancer-specific chromatin interactions within the TADs that are enriched at regulatory elements such as enhancers, promoters, and insulators, and associated with alterations in gene expression. We also show that differential chromatin interactions across regulatory regions occur within long-range epigenetically activated or silenced regions of concordant gene activation or repression in prostate cancer. Finally, we present a novel visualization tool that enables integrated exploration of Hi-C interaction data, the transcriptome, and epigenome. This study provides new insights into the relationship between long-range epigenetic and genomic dysregulation and changes in higher-order chromatin interactions in cancer.

Electric field-induced changes of domain structure and properties in La-doped PZT—From ferroelectrics towards relaxors

Electromechanical properties and crystal and domain structures of piezoelectric ceramics from the Pb1−xLax(Zr0.65Ti0.35)1−x/4O3 (x/65/35 PLZT) solid solution system were systematically analysed by electrical measurements, X-ray diffraction and scanning electron microscopy. The compositionally-driven phase transition from a rhombohedral ferroelectric into a pseudocubic relaxor state is accompanied by a decrease in domain size and changes in domain morphology. SEM analyses of the ex-situ poled samples showed that only in the ferroelectric compositions domain configuration changed, while in the relaxor compositions no domain changes were detected. In order to evaluate the extrinsic contribution to enhanced piezoelectric properties in relaxors, in-situ environmental scanning electron microscopy analyses with applied external electric field were performed. Extrinsic effects as a result of poling were predominant in the ferroelectrics, whereas the intrinsic effect prevailed in the relaxors. Finally, a model of electric field-induced displacements as a result of decreasing domain size for the ferroelectric-to-relaxor PLZT materials was proposed.