Observation Of Domain Structure Research Articles

High-resolution observations of temperature-dependent magnetic domain structures withinGaxMn1−xAsby Lorentz microscopy

The observation of magnetic domain structures within an in-plane magnetized ${\mathrm{Ga}}_{x}{\mathrm{Mn}}_{1\ensuremath{-}x}\mathrm{As}$ dilute magnetic semiconductor on the submicronmeter scale by Lorentz microscopy is described. A micronmeter-scale domain substructure is found to be characteristic of the micromagnetics of the ${\mathrm{Ga}}_{x}{\mathrm{Mn}}_{1\ensuremath{-}x}\mathrm{As}$ sample. Due to the competition of temperature-dependent biaxial and uniaxial anisotropy, conventional zigzag and unusual segmented domain structures are identified, with the latter exhibiting spontaneous reorganization with varying temperature. The experimental results are compared with micromagnetic simulations.

Irreversible phase transition and spontaneous strain in CsHSO 4

We have carried out DTA, X-ray measurements and the optical observation of domain structure using the polarizing microscope, in order to investigate the mechanism of irreversible phase transitions observed at around 350 K ( T III–IV) and 380 K ( T II–III) in CsHSO 4. It is found from the result of DTA measurement that with decreasing temperature from 430 K (in the phase I) the irreversible phase transitions at T III–IV and T II–III are not observed at first day, but these irreversible phase transitions are observed after 12 days. Moreover, with increasing temperature, ferroelastic domain structure changes at III–IV and II–III phase and disappears with the superprotonic phase transition at 414 K ( T I–II). It is also found that a lot of small ferroelastic domains are observed, after the temperature decreases from 430 K of phase I to 300 K. The size of these domains gradually increases, and no change of domain size is observed. Considering that the observed domains are ferroelastic ones, the change of domain structure is caused by the change of spontaneous strain. From these results it is deduced that the increase in spontaneous strain is closely related to the appearance of irreversible phase transition.

Simultaneous observation of magnetic domain structure and topography of Fe70Co30 using scanning Lorentz force microscopy

The surface topography and the distribution of stray magnetic flux density of Fe70Co30 are observed simultaneously by using scanning Lorentz force microscopy (SLFM). The SLFM images of the magnetic domain of Fe70Co30 have been observed repeatedly, and they were found to be unaffected by the surface roughness and friction force. As compared to the magnetic force microscopy image, it can be inferred that small stray magnetic flux loops were detected near the sample surface in the SLFM image.

Imaging domains of hard magnetic materials by SEM and MFM

The paper deals with observation of the magnetic domain structure of hard magnetic materials by the colloid-scanning electron microscopy (colloid-SEM) technique and the magnetic force microscopy (MFM) method. The specimens studied were anisotropic sintered Nd–Fe–B-based and SmCo 5 magnets, produced by powder metallurgy route. Observations of the magnetic microstructure were carried out in the thermally demagnetized state of the magnets at the surface perpendicular to the alignment axis. The domain structure is of complicated character. The coarse domain pattern consists of the main domains (forming a maze pattern near the specimen surface) and surface reverse spikes. Besides the coarse domain structure, the presence of fine scale surface domains is revealed by MFM.

In situ observations of domain structures and magnetic flux distributions in Mn-Zn and Ni-Zn ferrites by Lorentz microscopy and electron holography

Domain structures and magnetic flux distributions in Mn-Zn and Ni-Zn ferrites are investigated by in situ observations with Lorentz microscopy and electron holography. In situ Lorentz microscopic observation with the magnetic field applied reveals that the domain walls in Mn-Zn ferrite move easily across the grain boundary. On the other hand, each grain of Ni-Zn ferrite is magnetized by domain wall motion inside the grain. By taking a series of holograms with adjustment of the optical axis and astigmatism while the magnetic field is applied, we succeeded in observing the change in magnetic flux distribution quantitatively. Eventually, it is clarified that magnetization rotation does not take place in the magnetization process of Ni-Zn ferrite. The domain wall widths delta in Mn-Zn and Ni-Zn ferrites are evaluated to be 73 and 58 nm, respectively. Furthermore, through direct observation of the domain structure in Ni-Cu-Zn ferrite with Lorentz microscopy, it is found that the grains with size below 1.5 microm diameter are single domain.

Indirect Observation of Inner Domain Structure in Nd2Fe14B Sintered Magnets

Domain structures in sintered Nd2Fe14B magnets were studied using Kerr effect microscopy (KEM) and magneto-force microscopy (MFM). In the direction perpendicular to the crystal c-axis (c-plane), a fine maze domain structure was observed using KEM, but an only unclear complex structure can be obtained using MFM. After 5T pulse magnetization, both observation methods gave clear monotonous images of many magnetized grains and local fine domain structures with strong contrast in limited numbers of grains. On the other hand, in the direction of parallel to the c-axis (in a sense, a-plane), only bright or dark grains as a whole grain, were observed using both methods. These observations can be explained as that the surface demagnetized grains have a role of permeable medium of the magnetic fluxes from the inner domains. As a conclusion, when the inner grains generate sufficient magnetic fluxes to magnetize the surface no-coercive grains, the inner domain structures of the sintered Nd2Fe14B magnets can be observed using KEM and MFM.

Observation of magnetic domain structures in [formula omitted

We investigated ferromagnetic domain structures for La 1 - x Sr x MnO 3 ( x = 0.125 , 0.175, 0.300), as functions of x and temperature by means of low-temperature Lorentz electron microscopy. We have observed the change of magnetic domain structures accompanied with the orthorhombic (monoclinic or triclinic)-to-rhombohedral phase transitions with respect to the chemical composition. In addition, the transition of the magnetic domain structure in the x = 0.175 compound, which exhibits the orthorhombic-to-rhombohedral phase transition at ∼ 190 K , has been observed with changing in temperature.

Observation of step-induced magnetic domain formation in La1−xSrxMnO3 thin films by photoelectron emission microscopy

Magnetic domain formation in thin films of La1−xSrxMnO3 (LSMO) with x=0.2 and 0.4 epitaxially grown on stepped SrTiO3 (001) substrates has been investigated by photoelectron emission microscopy. The magnetic domains show a stripe structure elongated along the step directions, indicating uniaxial magnetic anisotropy induced by step structures. We have also found that the magnetization of the magnetic domains is slightly meandering at domain boundaries. The existence of the additional structures suggests that the magnetic domains in LSMO films are also influenced by biaxial magnetocrystalline anisotropy. The direct observation of the magnetic domain structures suggests that the competition between the two magnetic anisotropies may play an important role in magnetic properties in LSMO films.

Thermal Expansion and Phase Transformation Observation in Cs2BX4 Crystals

The results of studies for thermal expansion and optical indicatrix rotation at the ferroelastic phase transition, along with the domain structure observations for Cs2HgCl4, Cs2HgBr4 and Cs2CdBr4 crystals are presented. On the basis of the literature data and the results of our studies for the heterophase structure, domain structure and thermal expansion, the phase diagram common for Cs2HgCl4, Cs2HgBr4 and Cs2CdBr4 crystals is proposed.

Observation and manipulation of the as-grown maze domain structure in lead germanate by scanning force microscopy

The ferroelectric domain structure of single crystalline Pb5Ge3O11 was inspected and manipulated using piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM). The irregularly shaped three-dimensional maze reflecting the as-grown domain structure on the micron and submicron scale was resolved with both PFM and KPFM. The temporal stability and recovery of that equilibrium structure was tested with macroscopic and local electric fields. Fractal analysis was applied for quantitative characterization of the complicated domain geometry. While spatially extended fields lead to a partial decay of the maze structure, local electric fields applied by the PFM tip result in addition in pronounced surface charging. The time constants of charge decay were extracted by KPFM and could be attributed to mobile charge redistribution and backswitching.

Effect of internal bias field on domain switching in (CH3NH3)5Bi2Br11 crystal

In this report we investigate the microscopic features of 180° domain wall dynamics and relate its dynamics to the defect structure in unipolar methylammonium bromobismuthate, (CH3NH3)5Bi2Br11, single crystal. The switching and spontaneous backswitching processes have been studied by observation of domain structure by using nematic liquid crystal method and by switching current registration. We found a two-step relaxation decay of polarization induced by Eb; the fast one decays on the time scale of milliseconds, while the slow one lasts over seconds. In the late-time regime, the stretched-exponential function was used as an empirical fit of relaxation data.

Carrier-controlled ferromagnetism in transparent oxide semiconductors

The search for an ideal magnetic semiconductor with tunable ferromagnetic behaviour over a wide range of doping or by electrical gating is being actively pursued as a major step towards realizing spin electronics. A magnetic semiconductor having a high Curie temperature, capable of independently controlled carrier density and magnetic doping, is crucial for developing spin-based multifunctional devices. Cr-doped In(2)O(3) is such a unique system, where the electrical and magnetic behaviour-from ferromagnetic metal-like to ferromagnetic semiconducting to paramagnetic insulator-can be controllably tuned by the defect concentration. An explicit dependence of magnetic interaction leading to ferromagnetism on the carrier density is shown. A carrier-density-dependent high Curie temperature of 850-930 K has been measured, in addition to the observation of clear magnetic domain structures in these films. Being optically transparent with the above optimal properties, Cr-doped In(2)O(3) emerges as a viable candidate for the development of spin electronics.

Self‐organized and highly ordered domain structures within swarms of Myxococcus xanthus

Coordinated group movement (swarming) is a key aspect of Myxococcus xanthus' social behavior. Here we report observation of domain structures formed by multiple cells within large three-dimensional swarming groups grown on amorphous glass substrates, using the atomic force microscope (AFM). Novel analyses revealed that 90% of the wild type swarms displayed some form of preferential cell alignment. In contrast, cells with mutations in the social and adventurous motility systems displayed a distinct lack of cell alignment. Video microscopy observations of domain features of in vivo swarming M. xanthus cells were also consistent with the AFM data. The results presented here reveal that unique domain formation within swarms of wild type cells is a biologically driven process requiring the social and adventurous motility systems and is not a statistical phenomenon or thermodynamic process arising from liquid crystal behavior.

Applications of high-resolution MFM system with low-moment probe in a vacuum

Magnetic force microscopy (MFM) is very useful for observing magnetic domain structures. However, due to stray fields from an MFM probe, observations of small magnetic domain structures are limited. The authors have developed a high-resolution MFM system that utilizes a low-moment probe and a quality (Q)-controlled prove driver, which allows high-quality measurement in a vacuum without disturbing domain structures. Using this system, a resolution finer than 20 nm was achieved. In this paper, the advantages of this MFM are demonstrated using a Permalloy honeycomb nanonetwork and a Permalloy semicircular loop.

In-situ Observation of Magnetic Domain Structure by Electron Holography and Lorentz Microscopy with a Magnetizing Stage

Extract HTML view is not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button. Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

Some Bristol–Prague explorations in x-ray topography

This paper briefly chronicles a long-standing and productive collaboration between the Institute of Physics, Czech Academy of Science and the H H Wills Physics Laboratory. It began in early 1962 with a brief visit to Bristol by Milena Polcarová. The initial aim, successfully achieved, was the mapping by transmission topography of dislocations in melt-grown single crystals of a Fe–Si alloy. A novel by-product was the x-ray topographic observation of internal magnetic domain structures in specimen plates prepared in both (110) and (112) orientations. In the alloy studied, which contained about 3 wt% Si, the directions of easy magnetization are ⟨ 100 ⟩, and domain boundaries are either 180° or 90° Bloch walls. The latter walls can generate strong x-ray diffraction contrast, but no contrast from 180° walls is expected. In the (110) plates x-ray topography revealed complex internal domain structures containing 90° walls, some previously unsuspected on evidence of optical micrography of colloid patterns (Bitter patterns). Certain details of these structures remain a puzzle to this day! In (112) specimens, in which no direction of easy magnetization lies in the plate surface, the specimen is filled with a hierarchy of domains, diminishing in scale towards the surfaces in order to minimize magnetostatic energy due to free poles. However, in (112) plate thicknesses less than ∼20 µm, x-ray topographs recorded internal domain structures sufficiently uncomplicated for their main features to be interpreted. This was achieved by F C Frank in the early 1960s, but not published till 1993! During a 1968 visit to Bristol by Polcarová it was discovered that under appropriate diffraction conditions x-ray topographic contrast from 180° Bloch walls was just detectable. This finding was not published till 1991. More recent work with Prague specimens has applied synchrotron x-ray reticulography at Daresbury, showing that this technique can be informatively used with lightly-deformed Fe–Si bicrystals.A very different enterprise was the Bristol method of producing x-ray moiré patterns by superposing one crystal plate upon another, achieved in 1967. This project gained from Czech collaboration through the skilful participation of J Brádler, on leave from Prague.

Changes of magnetic domain structure induced by temperature-variation and electron-beam irradiation in Pr0.5Sr0.5CoO3

In situ observation of magnetic domain structures of Pr0.5Sr0.5CoO3 was made by Lorentz electron microscopy to reveal an unusual magnetic behavior around 120K below the Curie temperature (TC∼220K). The observations in a cooling run clearly showed that the magnetic domain structure changes below about 90K and that the transformed domain structure remains unchanged down to 20K. Furthermore, it was found that an electron-beam irradiation in an electron microscope induces a reversible transformation of the magnetic domain structure at 20K. Possible mechanisms of such magnetic-domain structural changes are discussed.

Observation of ferroelectric domains in bismuth-layer-structured ferroelectrics using Raman spectroscopy

Raman spectroscopy has been used to investigate the domain structures in bismuth-layered-structured ferroelectrics (BLSFs). In Bi 4Ti 3O 12 single crystal, the lowest frequency mode (soft mode) at ∼30 cm −1 appears exclusively for the xx polarization configuration ( x ∥ polar axis ). We found that the polarization dependence of the Raman signal exhibits spatial symmetries that reflect the presence of different domain variants present in Bi 4Ti 3O 12. This highly anisotropic character of the soft mode shares with other BLSFs such as Bi 3.25La 0.75Ti 3O 12 and SrBi 2Ta 2O 9, which demonstrate the usefulness of the soft-mode spectroscopy for the study of ferroelectric domain structures in BLSFs. We also applied Raman spectroscopy to in situ observation of domain structures in Bi 4Ti 3O 12 under applied electric field.

Observation of Magnetic Domain Structure of Micro Magnetic Materials and Magnetic Thin Films by Photoemission Electron Microscope (PEEM)

The photoemission electron microscopy using synchrotron radiation (SR-PEEM) combined with the X-ray circular and linear dichroism (XMCD and XMLD) is one of the most powerful techniques to investigate the magnetic domain structure of micro magnetic materials or surfaces and interfaces of magnetic thin films. With the method, we can observe the magnetic domain structure directly to a very high spatial resolution. In this paper, the technique of SR-PEEM for the observation of the magnetic domain structure and its applications to the Ni-micro ring, and the ferromagnetic/antiferromagnetic interface, i.e. the Fe wedge/NiO(001), are introduced.

Observation of magnetic domain structures in manganese oxides by Lorentz electron microscopy

Observation of magnetic domain structures in manganese oxides by Lorentz electron microscopy