Observation Of Domain Structure Research Articles

In-situ observation of magnetic domain structures in nanocrystalline soft magnetic materials by differential-phase-contrast scanning transmission electron microscopy

In-situ observation of magnetic domain structures in nanocrystalline soft magnetic materials by differential-phase-contrast scanning transmission electron microscopy

Large topological Hall effect and in situ observation of magnetic domain structures in the Mn2FeSn compound

The search for novel topological magnetic domain structures such as magnetic skyrmions, bubbles and vortices, and relative physical effect has always been the focus of spintronics devices. Here, the magnetism, transport properties and magnetic domain structures of the polycrystalline hexagonal Mn2FeSn compound are studied in detail. We find the strong texture along c-axis in this bulk compound owing to large temperature gradient between the bottom and top of the ingot during the preparation process. The resistivity resulting from topological Hall effect reaches about 5.19 μΩ cm at 50 K in the sample of compound obtained by cutting along perpendicular texture direction. Spontaneous nanoscale magnetic bubbles have directly been observed at low temperature due to the competition among the magnetocrystalline anisotropy, antiferromagnetic, and ferromagnetic exchange interactions as decreasing temperature. It is the formation of non-collinear or non-coplanar spin configuration that causes the obvious topological Hall effect. Additionally, the biskyrmion-like state can be obtained with evolution of stripe domains under an appropriate magnetic field. Based on these results, this study of Mn2FeSn magnet may be beneficial to the development for exploring novel magnetic spin textures.

Oxygen tracer diffusion analysis and observation of domain structure in quenched (Bi0.5Na0.5)TiO3 ceramics

Lead-free ferroelectric and piezoelectric ceramics, (Bi0.5Na0.5)TiO3 [BNT] ceramics were prepared by controlling the quenching rate. The quenching effects mainly caused an increase in lattice distortion 90-α and T d, contribution of electrical properties and ordered structural phase transitions. In this study, we analyzed oxygen tracer diffusion and examined domain structures for quenched BNT ceramics, and then we proposed a mechanism for the quenching effect. As a result, the diffusion coefficients D of 18O tracer for the OF and quenched samples were 2.5 × 10–11 and 1.8 × 10–11 cm2 s−1, respectively, and there were no significant differences in oxygen vacancies after quenching. The correlation between the quenching effect and oxygen vacancies was also examined in BNT with hard and soft dopants. However, the contribution of oxygen vacancies was small thus, the correlation between the quench effect and oxygen vacancies was low. On the other hand, the domain structure of BNT ceramics was observed and the domain size of OF-BNT was around 20 nm. This is a typical domain size for BNT ceramics. In contrast, the domain size of the quenched BNT was 40 nm. Thus, quenching increased the domain size and decreased their density. Consequently, we propose that the domain structure is strongly correlated with the quench-induced increase in lattice distortion and T d, its contribution to electrical properties, and ordered structural phase transitions.

Pulse-poling and characterization of (Na,K)NbO3 ceramics

Conventional direct current (DC)-poling and three different types of pulse-poling were performed on MnO-added Na0.55K0.45NbO3 (NKN) ceramics. While NKN with DC-poling at 4.0 kV mm−1 for a poling time (t p) of 100 s showed a piezoelectric charge coefficient d 33 of 141.3 pC N−1, an almost equivalent d 33 (141.3 pC N−1) was recorded by pulse-poling in only 10 s under a unipolar electric field of 4.0 kV mm−1, with either triangular, or rectangular waveform. Especially when applying a triangular waveform, d 33 was enhanced remarkably with increasing the number of pulse cycles. In contrast, NKN ceramics poled by alternating current (AC) electric field showed a d 33 of less than 135 pC N−1 under any condition. Polarization–electric (P–E) field responses, and domain structure observations via scanning electron microscopy, showed the different poling behaviors for the various poling techniques. These results suggested that the pulse-poling method under unipolar electric field is an efficient poling procedure for NKN ceramics.

Observation of domain structure in non-collinear antiferromagnetic Mn3Sn thin films by magneto-optical Kerr effect

We perform hysteresis-loop measurement and domain imaging for (11¯00)-oriented D019-Mn3+xSn1-x (−0.11≤x≤0.14) thin films using the magneto-optical Kerr effect (MOKE) and compare it with the anomalous Hall effect (AHE) measurement. We obtain a large Kerr rotation angle of 10 mdeg, comparable with bulk single-crystal Mn3Sn. The composition x dependence of AHE and MOKE shows a similar trend, suggesting the same origin, i.e., the non-vanishing Berry curvature in the momentum space. Magnetic domain observation at the saturated state shows that x dependence of AHE and MOKE is explained by the amount of the reversible area that crucially depends on the crystalline structure of the film. Furthermore, in-depth observation of the reversal process reveals that the reversal starts with nucleation of sub-micrometer-scale domains dispersed in the film, followed by domain expansion, where the domain wall preferentially propagates along the [112¯0] direction. Our study provides a basic understanding of the spatial evolution of the reversal of the chiral-spin structure in non-collinear antiferromagnetic thin films.

Magnetic domain reversal induced by thermal activation in SmCo alloy

The SmCo alloys are widely used in the field of precision instruments and high temperatures due to their excellent temperature stability. At present, the effect of high temperature on the domain structure of SmCo alloy lacks sufficient study. In this paper, the effect of temperature on the magnetic domain of type 2:17 SmCo alloy was investigated by domain structure observation and micromagnetic simulation. After heating at 240 ℃ and 300 ℃, the reverse domains could be observed on the surface of the magnet, and the domains nucleated at the center region of the grains and then expanded into maze domains. The in-situ heating test using Lorentz electron microscope confirms, from a microscopic point of view that thermal activation causes irreversible movement of the walls of the domains. It was found by the comparison between batch heating tests and continuous heating tests that part of the inverted domains are unstable during the cooling from high temperature down to room temperature, and the micromagnetic simulation results verified that without the temperature field and magnetic field, the unstable inverted domains would disappear under the influence of the interaction, and the domains pinned by the phase boundary will be stably retained. The micromagnetic simulation results reveal that the nucleation sites of the reverse domains in the SmCo alloy are at the intersection of the 2:17R phase and Zr-rich phase, which is due to the lower pinning field of the Zr-rich phase.

Temperature-induced phase transition of -oriented 0.92Na0.5Bi0.5TiO3-0.08Bi(Zn0.5Ti0.5)O3 lead-free single crystals

Lead-free single crystals 0.92Na0.5Bi0.5TiO3-0.08Bi(Zn0.5Ti0.5)O3 (NBT-BZT) near the morphotropic phase boundary (MPB) were grown by the top seeded solution growth (TSSG) method. The temperature-induced phase transition behaviour of <001>-oriented NBT-BZT lead-free single crystals was investigated. The relationship between dielectric properties and temperature exhibited phase transition temperatures of approximately 200 °C and 328 °C. The thermal evolution of phase structure in NBT-BZT single crystals was further studied by Raman spectroscopy, and the structural phase transitions from rhombohedral (R) to monoclinic (M) phases, then from monoclinic to tetragonal (T) phases were confirmed by optical domain structure observation. These results are beneficial for understanding the nature of ferroelectric phase transitions.

Structure of Alloys for (Sm,Zr)(Co,Cu,Fe)z Permanent Magnets: II. Composition, Magnetization Reversal, and Magnetic Hardening of Main Structural Components.

Experimental series of alloys for (Sm,Zr)(Co,Cu,Fe)Z permanent magnets are presented in the concentration ranges that provide wide variations of (4f)/(4d)/(3d) ratios of comprising elements. Optical metallographic analysis, observation of the surface domain structure upon magnetization reversal (Kerr effect), electron microprobe analysis, and measuring the major hysteresis loops of samples at different stages of heat treatment are used to study processes related to the development of the highly coercive state of these samples. It was found that the volume fractions of two main structural components A and B, which comprise 90% of the total sample volume, rigorously control the coercivity at all stages of thermal aging. At the same time, structural components A and B themselves in samples being in the high-coercivity state differ qualitatively and quantitatively in the chemical composition, domain structure and its development in external magnetic fields and, therefore, are characterized by different morphologies of the phases comprising the structural components. Two stages of phase transformations in the sample structure are observed. During isothermal annealing, the cellular structure develops within the B component, whereas, during stepwise (slow) cooling or quenching from the isothermal aging temperature to 400 °C, a phase structure evolves within both the cell boundaries in B and the structural component A. The degree of completion of the phase transformations within micro- and nano-volumes of the components determines the ultimate hysteretic characteristics of the material.

Microscopic origin of asymmetric magnetization reversal of Co/Pt multilayers with perpendicular magnetic anisotropy

We have comprehensively investigated asymmetric magnetization reversal behaviors of (x-Å Co/7.7 Å Pt)5 multilayers (x = 3.1 and 4.7) with perpendicular magnetic anisotropy. Our direct observation of magnetic domain structures by means of magneto-optical microscopy reveals that the asymmetry arises both from nucleation and wall-motion processes. An asymmetric nucleation behavior is observed, which could be originated from the preexisting non-reversed domains which might have a reproducible or random spatial distribution, controllable by tuning the field profile. An asymmetric wall-motion behavior stemming from asymmetric stripe domain evolution is also observed.

Direct observation of multiple magnetic transitions in the La3NiGe2-type compounds

By using Lorentz transmission electron microscopy, we show the real-space observation of magnetic domain structures in orthorhombic polycrystalline (Tb1−xGdx)3NiSi2 (x = 0, 0.4) compounds. The significant changes in magnetic domains related to multiple magnetic transitions were identified. A spin reorientation transition was further studied and a type of magnetic domain structure with two mutually perpendicular domain walls was observed, where the magnetic vortices and antivortices appeared as an array. This magnetic domain pattern evolves with temperature, which corresponds well to the spin reorientation transition and is related to the change in ferromagnetic and noncollinear magnetic components.

Imaging switchable magnetoelectric quadrupole domains via nonreciprocal linear dichroism

Parity-odd magnetoelectric multipoles such as magnetic quadrupoles and toroidal dipoles contribute to various symmetry-dependent magnetic phenomena and formation of exotic ordered phases. However, the observation of domain structures emerging due to symmetry breaking caused by these multipoles is a severe challenge because of their antiferromagnetic nature without net magnetization. Here, we report the discovery of nonreciprocal linear dichroism for visible light (~4% at 1.8 eV) in a magnetic quadrupole ordered phase of antiferromagnetic Pb(TiO)Cu4(PO4)4, which enables the identification of magnetic quadrupole domains of opposite signs. Symmetry considerations indicate that nonreciprocal linear dichroism is induced by the optical magnetoelectric effect, i.e., the linear magnetoelectric effect for electromagnetic waves. Using the nonreciprocal linear dichroism, we successfully visualize spatial distributions of quadrupole domains and their isothermal electric-field switching by means of a transmission-type polarized light microscope. The present work exemplifies that the optical magnetoelectric effect efficiently visualizes magnetoelectric multipole domains responding to external perturbations.

Influence of combined mechanical stress on magnetic structure in magnetic microwires

The experimental observation of the spiral domain structure has opened a new possibility of the fine control of the domain structure with different magnetization states in magnetic microwires which are the base elements of the magnetic sensors. Here we demonstrate that the tuning of magnetic domain structures in amorphous microwires can be engineered by the combination of tension and torsion mechanical stresses.

Development of a scanning soft X-ray spectromicroscope to investigate local electronic structures on surfaces and interfaces of advanced materials under conditions ranging from low vacuum to helium atmosphere.

A scanning soft X-ray spectromicroscope was recently developed based mainly on the photon-in/photon-out measurement scheme for the investigation of local electronic structures on the surfaces and interfaces of advanced materials under conditions ranging from low vacuum to helium atmosphere. The apparatus was installed at the soft X-ray beamline (BL17SU) at SPring-8. The characteristic features of the apparatus are described in detail. The feasibility of this spectromicroscope was demonstrated using soft X-ray undulator radiation. Here, based on these results, element-specific two-dimensional mapping and micro-XAFS (X-ray absorption fine structure) measurements are reported, as well as the observation of magnetic domain structures from using a reference sample of permalloy micro-dot patterns fabricated on a silicon substrate, with modest spatial resolution (e.g. ∼500 nm). Then, the X-ray radiation dose for Nafion® near the fluorine K-edge is discussed as a typical example of material that is not radiation hardened against a focused X-ray beam, for near future experiments.

Insights into magnetoelectric coupling mechanism of the room-temperature multiferroic Sr3Co2Fe24O41 from domain observation

The mechanism of a magnetoelectric coupling in a room-temperature multiferroic, $\mathrm{S}{\mathrm{r}}_{3}\mathrm{C}{\mathrm{o}}_{2}\mathrm{F}{\mathrm{e}}_{24}{\mathrm{O}}_{41}$, with the Z-type hexaferrite structure, is examined by three approaches: observations of domain structures and their field responses, measurements of magnetic-field effect on electric polarization, i.e., magnetoelectric effect, and phenomenological discussions on the interplay among coexisting order parameters. With use of a resonant soft x-ray microdiffraction technique, we visualized magnetic-field responses of two types of magnetic domains ascribed to ferrimagnetic and spiral components inherent in a transverse conical magnetic structure of the hexaferrite. A simultaneous inversion of these magnetic domains by a magnetic-field reversal was observed, meaning that the process of a magnetization reversal corresponds to a 180\ifmmode^\circ\else\textdegree\fi{} rotation of the cone axis. The reversal process of the magnetic structure, together with experimental results of the magnetoelectric effect, leads us to the conclusion that the magnetoelectricity in the Z-type hexaferrite originates mainly from the spin-dependent metal-ligand orbital hybridization, with minor contribution from the asymmetric spin-exchange interaction. Furthermore, such a mechanism is discussed by the symmetry analysis based on the Landau theory and is well described in terms of couplings among the coexisting order parameters included in the free energy. Thus, observations on field responses of multiple domains in multiferroics provide insights into underlying microscopic magnetoelectric coupling mechanisms.

Second harmonic microscopy of poled x-cut thin film lithium niobate: Understanding the contrast mechanism

Thin film lithium niobate has been of great interest recently, and an understanding of periodically poled thin films is crucial for both fundamental physics and device developments. Second-harmonic (SH) microscopy allows for the noninvasive visualization and analysis of ferroelectric domain structures and walls. While the technique is well understood in bulk lithium niobate, SH microscopy in thin films is largely influenced by interfacial reflections and resonant enhancements, which depend on film thicknesses and substrate materials. We present a comprehensive analysis of SH microscopy in x-cut lithium niobate thin films, based on a full three-dimensional focus calculation and accounting for interface reflections. We show that the dominant signal in backreflection originates from a copropagating phase-matched process observed through reflections, rather than direct detection of the counterpropagating signal as in bulk samples. We simulate the SH signatures of domain structures by a simple model of the domain wall as an extensionless transition from a −χ(2) to a +χ(2) region. This allows us to explain the main observation of domain structures in the thin-film geometry, and, in particular, we show that the SH signal from thin poled films allows to unambiguously distinguish areas, which are completely or only partly inverted in depth.

Multi‐scale domain structure observation and piezoelectric responses for [001]‐oriented PMN‐33PT single crystal

AbstractMultiple phase coexistence contributes to the extraordinary piezoelectric behavior of (1‐x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) near the morphotropic phase boundaries (MPBs). By incorporating an optical path of crossed polarized light (PLM) into the commercialized Piezoelectric Force Microscope (PFM) (named as PLM‐PFM system), in situ domain structure observation from micro‐ to nanoscale, as well as measurement of the piezoelectric behavior for individual domains can be realized. For [001]‐oriented single crystal of 67Pb(Mg1/3Nb2/3)O3‐33PbTiO3 (PMN‐33PT), fine domain boundary structures of rhombohedral (R), tetragonal (T), and monoclinic (M) phases are revealed. Measurements of the electric field‐induced displacement as a function of the applied DC electric field (VDC) are performed for domains with different polarization vectors. Values for the electric field‐induced displacement are in descending order for c‐domains of the M, R, and T phases. For an individual phase of T or M, the displacement increases when the angle between the polarization vector and the applied electric field decreases. The multi‐scale perspective of the domain structures and the corresponding piezoelectric response helps in understanding the ultra‐high piezoelectric performance for PMN‐PT single crystals near MPB.

Lorentz TEM study of the magnetic microstructure in near-eutectoid Co-Pt alloys

Abstract In this paper, we report Lorentz Transmission Electron Microscopy (LTEM) observations of magnetic domain structures in a near-eutectoid Co 40 Pt 60 alloy. The crystallographic microstructure is characterized using conventional bright field/dark field TEM imaging. The magnetic induction orientation inside magnetic domains is extracted from Fresnel through-focus images by reconstructing the phase of electron wave using the transport-of-intensity equation. The alloy shows a nano-chessboard pattern composed of the L10 tetragonal and L12 cubic phases. The magnetization distribution in four neighboring L10 tiles in the nano-chessboard structure is found to follow a vortex/anti-vortex configuration to reduce the magnetostatic and magneto-crystalline anisotropy energies. An unconventional domain wall referred to as an inter phase magnetic domain wall (IPMDW) is observed at the inter-phase boundaries of L10 and L12 phases. Magnetic domain walls in other microstructures (tweed microstructure, macro-twinned structure, coarsened L10 plates) are also documented.

Direct observation of the stress-induced domain structure in lead-free (Na1/2Bi1/2)TiO3-based ceramics

In this work, the creep behavior of (Na1/2Bi1/2)TiO3-0.07BaTiO3 was characterized as a function of bias stress up to −500 MPa, revealing the time-dependence of the stress-induced relaxor-to-ferroelectric long-range order transformation. Creep strain was observed across a range of applied compressive stress levels, in particular at stresses approximately 50% above the critical coercive stress, indicating the significant time-dependence of the transformation on the long-range ferroelectric order. The macroscopic behavior is discussed in conjunction with ex situ piezoresponse force microscopy measurements that directly show the formation of ferroelectric domains in mechanically loaded relaxor ferroelectrics.

Three-dimensional imaging of ferroelectric domain structure in periodically poled lithium niobate using digital holographic tomography

An experimental method for three-dimensional (3D) imaging of ferroelectric domain patterns using digital holographic tomography is presented. The implementation of this method employs the curvilinear filtered back-projection. Our experimental method has been demonstrated on the imagining of the domain structure in a periodically poled lithium niobate single crystal. The developed method allows fast and accurate 3D observations of ferroelectric domain structures in the whole volume of the ferroelectric single crystals on the millimeter scale.

1p-A-6 STM及びAFMによる強弾性体MP_5O_ (M:La-Tb)の分域構造の観察

1p-A-6 STM及びAFMによる強弾性体MP_5O_ (M:La-Tb)の分域構造の観察