Changes In Domain Pattern Research Articles

Measurement of temporal evolution of antiferromagnetic domain change in nickel oxide driven by 2TO phonon mode excitation via pump-probe experiment

The temporal evolution of antiferromagnetic domain pattern changes under resonant excitation of the second-order transverse optical phonon mode in nickel oxide was investigated using mid-infrared free electron laser (MIR-FEL) pulses and visible nanosecond probe laser pulses at room temperature. We visualized the domain patterns through magneto-optical polarized microscopy in transmission and observed their temporal variation after the phonon excitation via MIR-FEL. We evaluated the differences throughout the timeline using the structural similarity index measure technique from domain images with and without MIR-FEL irradiation. We found that the MIR-FEL irradiation induces significant structural changes in the domain patterns. The maximum difference was observed at the timing of the MIR-FEL irradiation and exponentially recovered with the time constant of 1.4 ± 0.2 ms. This rather long-time constant could be owing to the spin relaxation, whilst further investigation is needed to confirm the underlying mechanism.

Post-acquisition upsampling method for scanning x-ray microscopy.

A method of post-acquisition upsampling for scanning x-ray microscopy is developed in this study to improve the spatial resolution beyond the Nyquist frequency as determined by the intervals of a raster scan grid. The proposed method is applicable only when the probe beam size is not negligibly small compared with the pixels that constitute a raster micrograph-the Voronoi cells of a scan grid. The unconvoluted spatial variation in a photoresponse is estimated by solving a stochastic inverse problem at a higher resolution than that at which the data are acquired. This is followed by a rise in the spatial cutoff frequency due to a reduction in the noise floor. The practicability of the proposed method was verified by applying it to raster micrographs of x-ray absorption in Nd-Fe-B sintered magnets. The improvement thus achieved in spatial resolution was numerically demonstrated via spectral analysis by using the discrete Fourier transform. The authors also argue for a reasonable decimation scheme for the spatial sampling interval in relation to an ill-posed inverse problem and aliasing. The computer-assisted enhancement in the viability of scanning x-ray magnetic circular dichroism microscopy was illustrated by visualizing magnetic field-induced changes in domain patterns of the Nd2Fe14B main-phase.

Strain engineering of the magnetic anisotropy and magnetic moment in NdFeO3 epitaxial thin films

Strain engineering is a powerful mean for tuning the various functionalities of ABO3 perovskite oxide thin films. Rare-earth orthoferrite RFeO3 materials such as NdFeO3 (NFO) are of prime interest because of their intriguing magnetic properties as well as their technological potential applications especially as thin films. Here, using a large set of complementary and advanced techniques, we show that NFO epitaxial thin films, successfully grown by pulsed laser deposition on (001)-SrTiO3, show a strong magnetic anisotropy below a critical thickness tc of 54 nm, associated with the occurrence of structural modifications related to symmetry and domain pattern changes. By varying the tensile misfit strain through the decrease of film thickness below tc, the amplitudes of in and out-of-plane magnetization can be continuously tuned while their ratio stays constant. Furthermore, different low-temperature magnetic behaviors are evidenced for strained and relaxed films, suggesting that the strain-induced structural state impacts the magnetic phase stability.

In situ imaging of temperature-dependent fast and reversible nanoscale domain switching in a single-crystal perovskite

Metal halide perovskites exhibit a rich crystal structure, with multiple phases as well as ferroelastic domains, which is crucial for the optical and electrical properties. The average crystal phase-transition temperatures can be shifted by size, strain, or defects, but it is not clear whether such differences can also appear locally within a single crystal. The experimental study of domain dynamics within nanocrystals is challenging and requires a method capable of probing crystal lattice variations with both high spatial and temporal resolution. Here, we show that in situ full-field diffraction x-ray microscopy can be used to image domains in a single crystal ${\mathrm{CsPbBr}}_{3}$ nanoplatelet as the temperature traverses the orthorhombic to tetragonal phase transition, at 150 nm spatial resolution and 6 s time resolution. The images reveal sudden domain pattern changes faster than the temporal resolution. Surprisingly, we observe substantial local variations during heating, with domain changes occurring at different temperatures within the single crystal. The nanoplatelet exhibits a high-temperature domain pattern completely different from the low-temperature one, but both patterns are reproducible, and we reversibly switch between them in multiple cycles. These results demonstrate that single ${\mathrm{CsPbBr}}_{3}$ crystals can exhibit substantial local variation of their basic crystal properties.

Field mapping and temperature dependence of magnetic domain memory induced by exchange couplings

Strong magnetic domain memory is achieved in [Co/Pd]IrMn exchange-biased ferromagnetic thin films when zero-field-cooled (ZFC) below their blocking temperature TB. By mapping out the amount of memory throughout the entire magnetization cycle, from nucleation to saturation, at different temperatures below and above TB, we discover how microscopic morphological changes in the magnetic domain patterns correlate with the macroscopic magnetic hysteresis, in the presence or absence of exchange couplings. Our unique inter-field correlation maps show that in the ZFC state, the film exhibits the highest amount of domain memory, exceeding 90%, when domain patterns are compared at the same field value, in the coercive region of the magnetization loop. However, domain patterns also cross-correlate surprisingly well when measured at different field values, on a wide field range centered about the coercive region. The shape and symmetry of the correlation maps provide further insights into the microscopic morphological changes in the domain patterns and the amount of reversibility in the reversal process, at the nanoscale.

Effect of ferroelastic domain pattern changes on the EPR spectra in TDM

This article presents polarized light microscopy studies of the ferroelastic domain structure and the analysis of electron paramagnetic resonance spectra of Cr3+ admixture ions in trigonal double molybdates. The correlation has been found between abnormal EPR lineshape and domain structure in ferroelastic phases of these crystals.

Stability and crossover of 71° and 109° domains influenced by the film thickness and depolarization field in rhombohedral ferroelectric thin films

The stability of domain patterns in rhombohedral ferroelectric films was studied using the minimum of free energy consisting of electrostatic and elastic energies. The converse piezoelectric effect due to the residual depolarization field was also considered. In the open-circuit condition, the 109° domain is more stable than the 71° one, which has a large depolarization field energy. By gradually decreasing the depolarization field energy, the stable domain pattern changes from 109° to 71° at a critical film thickness. This critical thickness of crossover from 109° to 71° domains is predicted to decrease with increasing residual depolarization field.

Effect of ferroic domain pattern changes on the Raman spectra of some ferroic crystals

The influence of changes in the pattern of ferroic domain structure on the Raman spectra of β-LiNH 4SO 4 and (NH 4) 3H(SO 4) 2 single crystals were studied. It was shown that the Raman spectra of β-LiNH 4SO 4 passed from the ferroelastic phase differ from those of “as-grown” crystal and those of the crystal, which was in the paraelectric phase. Significant changes could be observed in the Raman bands related to triply degenerated ν 3 and ν 4 vibrations of the SO 4 tetrahedron. Detailed temperature studies of the Raman spectra of β-LiNH 4SO 4 close to the paraelectric–ferroelectric phase transition, exhibit anomaly of some internal vibrations of SO 4 in the temperature range where a regular large-scale structure is observed. Different types of evolution of the ferroelastic domain structure and temperature behaviour of the donor and acceptor vibrations were shown while heating and cooling the (NH 4) 3H(SO 4) 2 crystal. Different values of temperature hysteresis were found in temperature studies of the ferroelastic domain structure (Δ T S ≅ 3–5 K) and in Raman spectra studies (Δ T S ≅ 12 K). No changes were observed in the pattern of ferroelastic domain structure at the temperature T II–III ≅ 265 K, at which C2/ c → P2/ n structural phase transition takes place. On the other hand, at T III–IV ≅ 135 K additional domains with W′-type of domain wall orientation were found.

Absorption of Mercury in Gold Films and Its Further Desorption: Quantitative Morphological Study of the Surface Patterns

A thin film of Au exposed to mercury vapor disrupts forming separated domains of AuHg amalgam. After evaporation of Hg at high temperature Au islands are formed and the domain pattern changes. A detailed quantitative morphological analysis and comparison of two types of surface patterns before and after the evaporation of Hg is performed. We have found that during the evaporation of Hg at high temperature the islands decrease their sizes and their shapes become more circular. The domain pattern formed by the amalgam domains is found to be characterized by one length scale. After the removal of mercury the characteristic length scale vanishes and the structure function takes the shape typical for the random droplet morphologies.

In-plane field induced structural change of magnetic domains in layered manganite La 1.36Sr 1.64Mn 2O 7

We present a study of structural change of the magnetic domains in La 1.36Sr 1.64Mn 2O 7 using magneto-optical effect of a garnet film mounted on the ab-plane of a crystal. The maze domain formed below 65 K changes into the stripe domain elongated along field direction by applying in-plane field. Under an offset field perpendicular to the plane, however, the domain pattern changes into bubbles. These domain patterns are stable even after removing the field. The in-plane field needed for such structural change becomes small at higher temperatures. These changes are similar to those observed in bubble garnet films.

Recent Understanding the Dielectric Relaxation Processes, Domain Evolution and Disordering in Cd 2 Nb 2 O 7 Pyrochlore

The wide-frequency dielectric dispersion (100 Hz-13 MHz) and optical observation in domain pattern changes of pyrochlore relaxor ferroelectric Cd 2 Nb 2 O 7 between 77 and 300 K are presented and discussed from the viewpoint of relaxor and glassy behaviour of the system. A model based on two-weakly-bonded-network description of the pyrochlore structure is suggested to explain developing a sequence of disordered states of different nature (relaxor, glassy, structurally incommensurable) in Cd 2 Nb 2 O 7 on a temperature scale.

Acoustic emission from different PZT

Acoustic Emissions (AE) in ferroelectrics originate from three major sources: domain pattern changes, electric discharges and microcracking. All three may play a significant roll as damage mechanisms for the long term reliability of these materials in actuator applications. In this publication, contributions of at least two mechanisms in commercial PZT's are presented and the feasibility of a unique assignment of emission signature to mechanism is discussed. Soft PZT's show a distinct threshold for the first appearance of AE during poling. Large strain changes in these materials due to “easy'’ domain wall motion do not yield AE while high strain levels generate cascaded events. Subsequent polarization reversals generate AE events at lower fields. Hard PZT's continuously generate AE during the whole hysteretic cycle with no observable field levels of “easy'’ deformation. Domain wall motion is contrasted to the energy release of elastically prestressed domain states, domain nucleation, discharges and microcracking.

Domain Patterns and Phase Transitions in Ferroelectric Crystal KNbO3

We have studied the domain configurations and structures of KNbO3 crystal in orthorhombic and tetragonal phases by polarizing microscopy. The phase transition processes among orthorhombic, tetragonal and cubic phases and thermal hysteresis during phase transitions are observed directly. Domain-pattern changes and the stable domain patterns during the phase transitions are discussed.

Lifshitz-type domain patterns observed in CoNbZr structures

A Lifshitz-type domain pattern containing wedge-shaped easy-axis oriented domains is shown which was observed using the Kerr effect in a 250 x 160 μm 2 pattern of amorphous soft-magnetic CoNbZr with a thickness of 0.75 μm. This pattern is similar to the one recently observed for a 140 μm wide NiFe element, but displays a small additional hard-axis oriented domain on the tip of the wedge-shaped domains. This domain pattern changes into an in-plane closure domain pattern when the width of the CoNbZr structure is decreased, and into an easy-axis domain pattern without closure domains when the CoNbZr is laminated by a nonmagnetic spacer having a thickness of 30 nm. For spacer thicknesses of 50 and 100 nm, an intermediate domain pattern containing smaller wedge-shaped domains and possessing some flux closure of the large easy-axis oriented domains around the nonmagnetic spacer along the edges of the structures was observed.

High-frequency permeability of laminated and unlaminated, narrow, thin-film magnetic stripes (invited)

The permeability of the magnetic material in a thin-film magnetic head is an important, but hard to characterize, parameter since the magnetic permeability depends on the head domain structure, the drive frequency, and the shape and size of the head. We have measured the high-frequency permeability from 1 MHz to 300 MHz, hysteresis loops, and domain structure of unlaminated and multilayer magnetic thin-films as a function of stripe width for arrays of long narrow stripes. Monolithic permalloy films and permalloy films laminated with SiO2 have been photolithographically patterned and ion-milled to create 3 to 1000 μm wide rectangles, 1 cm long, with the hard axis oriented along the long axis of the rectangles. The high-frequency permeability of each array of a given width is measured by the signal detected by a nonresonant butterfly-coil pickup loop when the film is driven by a uniform radio-frequency magnetic field generated by a strip-line waveguide. The changes in domain pattern as the film structure and stripe width are varied are observed with a Kerr-effect imaging microscope. In unlaminated films, which exhibit standard closure domains, a reduction in high-frequency permeability is observed in agreement with simple models when the closure domains become a significant fraction of the film area. In laminated films with thick magnetic layers, the transition from the laminated domain state to closure domains as the stripe width is decreased occurs where expected from straightforward energy arguments. However, for magnetic layers less than 1 μm thick, where a transition from the easy-axis laminated domain state to a uniform hard-axis state is expected as the stripe width is reduced, the films first change from the easy-axis state to a complicated, low-Kerr-contrast domain pattern before switching to the hard-axis state at much larger widths than predicted. While the laminated state and hard-axis permeabilities are frequency independent, the permeability of the intermediate state rolls off beginning at between 10 and 100 MHz. For still thinner magnetic layers (250 Å), the multilayer retains the high-permeability easy-axis laminated domain state to the narrowest width measured, 3 μm.

The effects of localised heating on the properties of laminated core material during high voltage impulse

The authors present results of a preliminary investigation into the relationship between the influence of high-voltage impulses and the magnetic-core properties of distribution transformers. Experiments recording domain movement have shown that localized hot-spot heating and imposed impulse voltage can alter the number of domain walls. With an applied alternating field, these changes in domain pattern are rapidly restored to normal. The resulting changes in core losses are very short lived and insufficient in themselves to account for thermal degradation of insulation material leading to failure of the transformer. The B-H loops following a voltage surge do not show any significant changes in loss.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Visualization of interaction between ferroelectric domains in GASH crystal by the electron microscope methods

Abstract Electron microscope decoration technique and scanning electron microscope were used to study the ferroelectric domain structure on matched faces of guanidinium aluminium sulphate hexahydrate (GASH). Fine changes in domain patterns caused by rearrangement of domains after cleaving the crystal were observed.

Domain behavior in sintered Nd-Fe-B magnets during field-induced and thermal magnetization change

On sintered Nd-Fe-B permanent magnets, magnetic domain pattern changes in applied fields and at elevated temperatures were observed by the Kerr effect. Patterns on pole and side faces were recorded for different magnetization states in fields up to 17 kOe at 20 °C, and remanent patterns at temperatures up to TC. They are qualitatively interpreted. On pole faces, most grains are multidomain even at remanence. But the surface domains seen are not characteristic of the magnet interior. Side faces show mostly single-domain grains at remanence. These images appear to reflect bulk behavior. Walls are strongly pinned at grain boundaries but move easily in the main magnetic phase, a behavior analogous to that of sintered SmCo5.

Losses in silicon-iron

Measurements of total power loss and domain-wall spacing have been made on individual grains in polycrystalline specimens of commercial grain-oriented 3% silicon-iron material. The loss-per-cycle against frequency characteristic of a grain is found to consist of discrete linear portions, which correspond to different domain-wall spacings. These changes in domain pattern result in a lower value of static hysteresis loss than expected and, therefore, a larger proportion of the total power loss must be attributed to the anomalous loss. From domain observations, it is concluded that a part of the anomalous loss is due to nonuniform flux distribution in the material and the overloading of the well-oriented grains.

An electron microscope investigation of the temperature dependence of the magnetization directions in cobalt and nickel

Abstract The domain structure of cobalt and nickel foils has been studied as a function of temperature in the range 20–400°c. The changes in domain pattern occurring with increase in temperature in prism oriented cobalt crystallites agree closely with the calculated magnetization directions obtained from known anisotropy data. In accord with the magnetization directions calculated from the known sign of the anisotropy constants of nickel, experimental evidence for a change in the easy direction of magnetization from ⟨111⟩ to ⟨100⟩ at about 100–150°c is presented.