Observation Of Domain Structure Research Articles

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

Surface modification and its role in the preparation of FeSi gradient alloys with good magnetic property and ductility

Realization of the effective Si penetration at a lower processing temperature is a challenge, but of significance in reducing the strict requirements for the equipment and realizing cost-cutting in production. In this work, we have modified the surface microstructure of Fe-3 wt%Si alloy by using surface mechanical attrition treatment. The modified surface microstructure is characteristic of nanocrystalline, which is found to significantly enhance the efficiency of subsequent Si penetration into the alloy, and successively leading to the decrease of penetration temperature up to 200 °C. As a consequence, the Si gradient distribution across thickness can be readily controlled by changing penetration time, and FeSi alloys with various gradients are prepared by chemical vapor deposition along with subsequent annealing process. The dependence of magnetic and mechanical properties on Si gradient for demonstrates that the increase of Si gradient reduces core losses, especially at higher frequencies, and meanwhile improves ductility of FeSi alloys as well. The mechanism underlying the effect of Si gradient is clarified by combining magnetostriction measurement and domain structure observations. This work provides a facile and effective way for achieving gradient FeSi alloys with good magnetic property and ductility.

Domain Structure and Spin Reorientation in TbCo5 and DyCo5 Intermetallics

In this paper, we study the spin-reorientation processes in DyCo5 and TbCo5 intermetallic compounds by direct observation of domain structure (DS) realignment during the easy plane—easy cone—easy axis phase transitions. In addition to the analysis of DS changes due to temperature induced spin reorientation, a description is given of a newly discovered effect of surface out-of-plane domain reorientation produced by abrasion and/or indentation of the surface of macroscopic samples with overall easy-plane magnetocrystalline anisotropy.

Microstructure and magnetism of Co2FeAl Heusler alloy prepared by arc and induction melting compared with planar flow casting

This paper is devoted to investigations of the structural and magnetic properties of the Co2FeAl Heusler alloy produced by three technologies. The alloys prepared by arc and induction melting have resulted in coarse-grained samples in contrast to the fine-grained ribbon-type sample prepared by planar flow casting. Scanning electron microscopy completed by energy dispersive X-ray spectroscopy, X-ray diffraction, Mössbauer spectroscopy, and magnetic methods sensitive to both bulk and surface were applied. The chemical composition was slightly different from the nominal only for the ribbon sample. From the viewpoint of magnetic properties, the bulk coercivity and remnant magnetization have followed the structure influenced by the technology used. Saturation magnetization was practically the same for samples prepared by arc and induction melting, whereas the magnetization of ribbon is slightly lower due to a higher Al content at the expense of iron and cobalt. The surface magnetic properties were markedly influenced by anisotropy, grain size, and surface roughness of the samples. The surface roughness and brittleness of the ribbon-type sample did not make domain structure observation possible. The other two samples could be well polished and their highly smooth surface has enabled domain structure visualization by both magneto-optical Kerr microscopy and magnetic force microscopy.

Electric-field effect on spin-wave resonance in a nanoscale CoFeB/MgO magnetic tunnel junction

We investigate the electric-field effect on the exchange stiffness constant in a CoFeB/MgO junction through the observation of the spin-wave resonance in a nanoscale magnetic tunnel junction. We evaluate the electric-field dependence of the stiffness constant from the separation between resonance fields for the Kittel and spin-wave modes under electric fields. The obtained stiffness constant increases when the interfacial electron density is decreased. This dependence is consistent with that determined from the observation of electric-field dependent domain structures.

Enhancement of perpendicular magnetic anisotropy and coercivity in ultrathin Ru/Co/Ru films through the buffer layer engineering

We present results on a study of the interplay between microstructure and the magnetic properties of ultrathin Ru/Co/Ru films with perpendicular magnetic anisotropy (PMA). To induce PMA in the Co layer, we experimentally determined thicknesses of the buffer and capping layers of Ru. The maximum value of PMA was observed for the Co thickness of 0.9 nm with the 3 nm thick capping layer. The effective anisotropy field (Heff) and coercive force (Hc) of the Co layer are very sensitive to the Ru buffer layer thickness (tb). The values of Heff and Hc increase approximately by two and ten times, correspondingly, when tb changes from 6 to 20 nm, owing to an increase in volume fraction of the crystalline phase as a result of the grains’ growth. PMA is found to be mainly enhanced by elastic strains induced by the lattice mismatch on the Ru/Co and Co/Ru interfaces, leading to the deformation of the Co lattice. The surface impact is determined to be less than 10% of the magneto-elastic contribution to the effective anisotropy. Observation of the magnetic domain structure by means of polar Kerr microscopy reveals that out-of-plane magnetization reversal occurs through the nucleation, growth, and annihilation of domains, where the average size drastically rises with the increasing tb.

Room temperature ferroelectricity in continuous croconic acid thin films

Ferroelectricity at room temperature has been demonstrated in nanometer-thin quasi 2D croconic acid thin films, by the polarization hysteresis loop measurements in macroscopic capacitor geometry, along with observation and manipulation of the nanoscale domain structure by piezoresponse force microscopy. The fabrication of continuous thin films of the hydrogen-bonded croconic acid was achieved by the suppression of the thermal decomposition using low evaporation temperatures in high vacuum, combined with growth conditions far from thermal equilibrium. For nominal coverages ≥20 nm, quasi 2D and polycrystalline films, with an average grain size of 50–100 nm and 3.5 nm roughness, can be obtained. Spontaneous ferroelectric domain structures of the thin films have been observed and appear to correlate with the grain patterns. The application of this solvent-free growth protocol may be a key to the development of flexible organic ferroelectric thin films for electronic applications.

Direct Observation of Ferroelectricity and Charge Separation Process in CH3NH3PbI3 Perovskite Solar Cell

In recent years, organometallic trihalide perovskites has attracted more and more attention for the application of solar cells. In particular, methylammonium (MA) lead triiodide (CH3NH3PbI3 or MAPbI3) has attracted the most attention and undergoes rapid development since it was first applied as light absorber in mesoscopic solar cells. Up to now, it has been demonstrated that the power conversion efficiency of MAPbI3 based solar cells can reach 20%, which is directly related to the favorable direct band gap, high carrier mobilities and long carrier diffusion length. To further improve the performance of MAPbI3 based solar cell, researchers have been focused on studying the otpical, electronic, and optoelectronic properties of MAPbI3 perovskites extensively. However, there is not a systematic study of its ferroelectric properties and the correlation between its ferroelectricity and its optoelectronic properties. Here, we report our direct observation of the ferroelectric domain structure in MAPbI3 thin film using piezoresponse force microscope (PFM). A strong evidence of the intrinsic ferroelectricity is that the ferroelectric domain structure has no correlation to its crystal domain structure, as shown in figure 1. Besides, we also observed the characteristic butterfly loop and hysteresis loop from pointwise experiment, to further verify the ferroelectricity. In addition to using PFM, we also directly observed the charge separation process by measuring the surface potential with Kelvin probe force microscope (KPFM). Under laser illumination when the charge carriers are generated, the surface potential will either decrease or increase depending on the device structure (p-i-n or n-i-p), which can be probed with KPFM and correlated with the surface topography as well. Our preliminary study shows that with AFM’s capability of localized probing, both the ferroelectric property and the optoelectronic properties can be measured and correlated to the structure, which can help us better understand the role of ferroelectricity in the high performance of organometallic trihalide perovskites. Figure 1

Foucault optical system by using a nondedicated conventional TEM

We have constructed an electron optical system for both Foucault imaging and small‐angle electron diffraction (SmAED) modes by using a nondedicated conventional transmission electron microscope. The objective lens is switched off as for Lorentz microscopy. An objective mini‐lens is utilized in order to make a crossover on the plane where a selected area aperture is located. The aperture works for an angular selection in the Foucault mode. The present electron optical system has two advantages: one is the independent control of the illumination and the imaging optics, and the other is the application of external magnetic fields to the specimen parallel to the optical axis with the objective lens. In SmAED mode, the maximum camera length is estimated to be approximately 1300 m. We succeeded in the observation of magnetic domain structures and SmAED patterns of the rhombohedral phase of La0.7Sr0.3MnO3 by using the present electron optical system. Copyright © 2016 John Wiley & Sons, Ltd.

Photographic observation of magnetic domain structure with three-dimensional local magnetization direction

The direction of magnetization of a magnetic material is possibly oriented three-dimensionally because of the presence of magnetic anisotropy field, self-demagnetizing field, and stray field. Therefore, the three-dimensional detection of the direction of magnetization is required. The method of magnetic domain observation by photographic imaging utilizing the Kerr effect is widely used. If the perpendicular magnetization components exist, there is a problem that obliquely incident light has superimposed longitudinal Kerr and polar Kerr effects. To perform the three-dimensional detection of magnetization direction, it is necessary to eliminate the influence of the polar Kerr effect from the Kerr effect of obliquely incident light. We report the photographic observation of the magnetic domain structure and the detection of the three-dimensional local magnetization direction using the Kerr effect, applying only an in-plane saturation magnetic field.

On ferroelastic phase transition in bis(imidazolium) L-tartrate crystal

ABSTRACTFerroelastic phase transition of the second order in the bis(imidazolium) L-tartrate crystal was studied with optical methods. Ferroelastic domain structure observations confirmed theoretically calculated orientation of domain walls along the a and c axis. The linear birefringence measurements were performed for main cuts of the crystal. The critical index for the order parameter was evaluated as 0.505, very close to a classical mean field value.

Effect of annealing on exchange stiffness of ultrathin CoFeB film with perpendicular magnetic anisotropy

The effect of annealing on the exchange stiffness of ultrathin CoFeB films with perpendicular magnetic anisotropy was investigated through the observation of magnetic domain structures by magneto-optic Kerr-effect microscopy. A significant reduction of the exchange stiffness after an annealing process was observed, which is in striking contrast to a previous report that studied thick CoFeB films with in-plane magnetic anisotropy. Our results suggest that interdiffusion of non-magnetic atoms from the adjacent layer into CoFeB layer reduces the exchange stiffness, which explains the difference between the annealing effect on ultrathin and the thick CoFeB films. Thus, it is critical to prevent annealing-induced interdiffusion in order to suppress undesired sub-volume switching that degrades thermal stability of a free-layer in spin-transfer torque magnetic random access memory.

Neutron Dark-Field Imaging of the Domain Distribution in the Intermediate State of Lead

The intermediate state (IS) of a type-I superconductor is characterized by coexistence of Meissner phase and normal conducting phase. Experiments on the topology of the IS show a variety of universal domain patterns which are also seen in various other physical, chemical or even biological systems on various length and time scales. The possibility to easily tune the domain structure of the IS by a variation of magnetic field or temperature ideally qualifies type-I superconductors as general model systems for the investigation of domain nucleation and distribution. However, the experimental observation of the IS domain structure was up to now restricted to either thin films or surfaces. We demonstrate how neutron grating interferometry (nGI) probes the IS domain distribution in the interior of a bulk single-crystalline lead sample. By means of nGI, we are able to visualize the field penetration process into the superconductor as well as the hysteretic behavior of the intermediate state morphology. Finally, the impact of nGI for investigations on bulk domain nucleation is discussed, as this technique is applicable on many other systems that reveal a phase separation on a micrometer length scale.

45° Induced Magnetic Anisotropy for Isotropic High-Frequency Permeability

High-frequency permeability spectra and magnetic domain structures of CoZrTa films with 45° induced magnetic anisotropy were investigated in order to realize integrated flux-closed magnetic inductors. Isotropic permeability was experimentally achieved for both in-plane parallel and transversal directions. The obtained relative permeability of $\sim 380$ for both the directions of the unpatterned sample is approximately half of the conventional hard-axis permeability as expected from a magnetization rotation model. Once the films are micropatterned, permeability is typically degraded by the formation of spike domains in addition to the demagnetization effect. Through the observations of the magnetic domain structures using magneto-optical Kerr effect microscopy, we found that the formation of the spike domains is suppressed for the smaller patterned structures due to the domain walls along the 45° axis. The relative permeability of $\sim 360$ is achieved in the low-frequency range for the micropatterned structure, promising the possibility of flux-closed magnetic inductors with large inductance enhancement.

Temperature observation of the evolution of the domain structure of triglycine sulphate by SEM

The experimental results of time and temperature studies of evolution of the domain structure of triglycine sulphate under the action of a SEM electron beam are presented. Direct domain-structure observations are performed via a heating and cooling device installed inside the SEM camera.

Electric field induced phase transition and domain structure evolution in (Pb, La)(Zr, Sn, Ti)O3 single crystal

Antiferroelectric (Pb, La)(Zr, Sn, Ti)O3 (PLZST) single crystals with composition in the vicinity of morphotropic phase boundary have been grown and studied. From electric measurements, Raman study, and observation of domain structures, we found an electric field induced antiferroelectric to ferroelectric phase transition accompanied with fifteen times of strain difference. After this phase transition, the metastable ferroelectric phase (FEin) is preserved with soften of A1(TO1) mode and increase of long-range force. Coexistence of tetragonal (T) and rhombohedral (R) domains has been observed in virgin sample. Electric field induced T to R phase transition is verified by both extinction angle and domain morphology changes. Clamping “polar” structure formed by the embedded R phase would contribute to increase of long-range force. The remarkable strain difference accompany with induced phase transition makes the PLZST single crystal a promising candidate for electric switch and actuator applications.

Magneto-optical imaging technique for hostile environments: The ghost imaging approach

In this paper, we develop an approach to magneto optical imaging (MOI), applying a ghost imaging (GI) protocol to perform Faraday microscopy. MOI is of the utmost importance for the investigation of magnetic properties of material samples, through Weiss domains shape, dimension and dynamics analysis. Nevertheless, in some extreme conditions such as cryogenic temperatures or high magnetic field applications, there exists a lack of domain images due to the difficulty in creating an efficient imaging system in such environments. Here, we present an innovative MOI technique that separates the imaging optical path from the one illuminating the object. The technique is based on thermal light GI and exploits correlations between light beams to retrieve the image of magnetic domains. As a proof of principle, the proposed technique is applied to the Faraday magneto-optical observation of the remanence domain structure of an yttrium iron garnet sample.

Observation of magnetic domain structure in anatase (Ti,Co)O2 thin film at room temperature

Magnetic domain structures in anatase (Ti,Co)O2 (001) epitaxial thin films were observed at room temperature. Magnetic force microscopy in vacuum enabled to observe submicrometer-sized maze domain. Variation of magnetic domain structure as functions of carrier density and Co content was in accordance with that of macroscopic magnetization representing close relationship between the bulk magnetism and magnetic domain structure. With increasing carrier density and/or Co content, the magnetic domain became larger with larger magnetic force signal mostly, where the ferromagnetic transition at carrier density of ∼2 × 1019 cm−3 was observed as an emergence of magnetic domain structure. Micromagnetic parameters were evaluated as functions of carrier density and Co content.

Investigation of the influence of different cutting procedures on the global and local magnetic properties of non-oriented electrical steel

The process of manufacturing iron cores for electric machines out of electrical steel sheets can strongly affect the magnetic properties of the material. In order to better understand the influence of cutting on the iron losses, a characterization of the magnetization behavior near the cutting edge is needed. The local magnetic properties of the material are modified by the cutting process which leads to an increase in the iron losses measured for 5mm wide ring core samples by nearly 160% at low inductions. We present investigations on the effect of cutting by observation of the magnetic domain structure of 0.35mm thick non-oriented electrical steel. By using the magneto-optical Kerr-effect on a ring samples the local magnetic properties of the material after processing are characterized in the form of domain wall displacements under an applied external ac-field. The influence of various cutting techniques on the magnetic properties was studied before and after stress relief annealing. This method allows a quantitative analysis of the influence of different cutting techniques on the micro-magnetic properties of non-oriented electrical steel for rotating machines.

Identification and mechanical control of ferroelastic domain structure in rhombohedralCaMn7O12

We report on observation of ferroelastic domain structure in single crystals of multiferroic ${\text{CaMn}}_{7}{\text{O}}_{12}$ at room temperature. Two types of ferroelastic domain wall are found, consistent with the material's rhombohedral symmetry that is reduced from cubic symmetry at higher temperatures. Using Raman spectroscopy along with other measurements, we develop a systematic method to determine the microscopic domain orientation. Moreover, we find a switching behavior of the domains, which allows us to detwin the crystals conveniently at room temperature using a moderate uniaxial compression. Our result paves the way for further spectroscopic study and domain engineering in ${\text{CaMn}}_{7}{\text{O}}_{12}$.