Visualization Of Domain Structure Research Articles

Research of Features Magnetic Permeability and Domain Structures in Fe2O3:GA Crystals near the Morin Transition

Specially picked up web-chamber is used for visualization of domain structure in hematite. An analysis of domain configuration shows, that domain structure of hematite in a basal plane represents multilayered structure which contains domains both in paralleled thickness and in the parallel basal planes. The temperature features of magnetic permeability and domain structures in Fe2O3:Ga crystals near the Morin transition are investigated. Observable changes of magnetic permeability and changes in domain structure confirm that transition from АFM to WFM occurs in the hematite with Ga impurity as transition of the first sort. Results of research of antiferromagnetic and weakly ferromagnetic resonances (AFMR and WFMR) in these compounds are presented.

Magnetic Imaging of Nanocomposite Magnets

Understanding the structure and magnetic behavior is crucial for optimization of nanocomposite magnets with high magnetic energy products. Many contributing factors such as phase composition, grain size distribution and specific domain configurations reflect a fine balance of magnetic energies at nanometer scale. For instance, magnetocrystalline anisotropy of grains and their orientations, degree of exchange coupling of magnetically soft and hard phases and specific energy of domain walls in a material. Modern microscopy, including Lorentz microscopy, is powerful tool for visualization and microstructure studies of nanocomposite magnets. However, direct interpretation of magnetically sensitive Fresnel/Foucault images for nanomagnets is usually problematic, if not impossible, because of the complex image contrast due to small grain size and sophisticated domain structure. Recently we developed an imaging technique based on Lorentz phase microscopy [l-4], which allows bypassing many of these problems and get quantitative information through magnetic flux mapping at nanometer scale resolution with a magnetically calibrated TEM [5]. This is our first report on application of this technique to nanocomposite magnets. In the present study we examine a nanocomposite magnet of nominal composition Nd{sub 2}Fe{sub 14+{delta}}B{sub 1.45} (14+{delta}=23.3, i.e. ''hard'' Nd{sub 2}Fe{sub 14}B-phase and 47.8 wt% of ''soft'' {alpha}-Fe phase ({delta}=9.3)), produced by Magnequenchmore » International, Inc. Conventional TEM/HREM study (Fig. 1-2) suggests that material has a bimodal grain-size distribution with maximum at d{sub max}=25 nm for Nd{sub 2}Fe{sub 14}B phase and d{sub max} = 15 nm for {alpha}-Fe phase (Fig.1c, Fig.2) in agreement with synchrotron X-ray studies (d{sub max}=23.5 nm for Nd{sub 2}Fe{sub 14}B [6]). Lattice parameters for Nd{sub 2}Fe{sub 14}B phase are a=8.80 and c=12.2 {angstrom}, as derived from SAED ring patterns (Fig.1a), again in good agreement with X-ray data. The fraction of large particles (of size 250 nm) is less then 57% of total amount of particles (Fig.1c, arrowed). Our new imaging technique allows visualization of domain structure in nanomagnets (Fig.3) in color code. Both projected magnetization and magnetic flux maps (Fig.3) reconstructed using Lorentz phase microscopy suggest a complex domain structure with an average domain size about 100x(100{approx}200) nm{sup 2} in a non-magnetized state. Large particles of darker contrast (of size {ge}50 nm, presumably {alpha}-Fe precipitates) or clusters of such particles act as effective concentrators for magnetic flux in nanocomposite matrix. The measured relative local-flux concentration by factor of 1.28 agrees well with theoretical ratio B{sub sat}({alpha}-Fe)/B{sub sat}(Nd{sub 2}Fe{sub 14}B)=1.31, strongly suggesting clustering of {alpha}-Fe particles that may have a detrimental effect on nanomagnet coercivity. Other smaller {alpha}-Fe particles (< 25 nm) do not disturb flux distribution, hence, they are magnetically coupled to Nd-Fe-B matrix grains as it was postulated by spring-exchange mechanism for nanocomposite magnets.« less

Simultaneous Single-Particle Tracking and Visualization of Domain Structure on Lipid Monolayers

A new method is presented that combines dual fluorescence microscopy and single-particle tracking (SPT) to investigate the impact of spatial inhomogeneities in membranes on lateral diffusion within Langmuir monolayers. In contrast to previous SPT experiments, random walks of individual fluorescent tracer particles and the structure of the membrane are simultaneously imaged. Monolayers of 1,2-dimyristoyl-sn-glycero-2-phosphoethanolamine (DMPE) in the liquid condensed/liquid expanded phase are used to model the inhomogeneous plasma membrane, while the fluorescent particles embedded in the membrane serve as model proteins. The interactions between tracers and the domain boundary and the resulting change in their random walks are directly observed. Since this technique permits systematic SPT studies of diffusion in inhomogeneous monolayers, its extensions to more biologically relevant monolayers are laid out as well.

Visualization of antiferromagnetic domain structures on as-grown NiO crystals by optical methods

The antiferromagnetic T-domain structures on a bulk NiO crystal surface could be visualized by means of incident-light types of microscope such as a differential interference microscope, a phase-contrast microscope and a high-dispersion interference contrast method. The visualization of the antiferromagnetic domain is possible due to the facial tilt which was induced in the NiO crystal due to the antiferromagnetic ordering below the Neel temperature. The lateral resolution of the present methods in visualization of the domain structure is about 1μm, which is better than that of X-ray or neutron topography. The tilt angle between each domain was measured by two-beam interferometry; the average experimental value (9′23″) agrees fairly well with the calculated value (8′24″). Direct observation of the movement and disappearance of the domain boundaries upon heating could also be carried out under the phase-contrast microscope.