Observation Of Domain Walls Research Articles

Relation of eddy current losses with domain wall movement of very thin 3%Si-Fe strip-wound cores

The authors discuss the relation of eddy current losses to dynamic domain behavior for very thin 3%Si-Fe strip-wound cores up to 5 kHz. The dynamic domain behavior was observed by using scanning electron microscope. The stripe domain structure B/sub 8/, and H/sub c/ were recovered after the strip was wound into a core and annealed above 800 degrees C. The wall bowing was negligible up to 1 kHz if the strip thickness was below 59 mu m. On the basis of these experiments, the measured domain wall numbers were compared with the calculated ones from Vm/He. The eddy current losses were calculated by applying the observed domain wall numbers to the modified Pry and Bean model and compared with the measured ones. The measured eddy current losses agreed comparatively well with the calculated ones above 500 Hz. The same tendency was obtained in the comparison of the observed domain wall numbers with the calculated ones. >

Preliminary Study of Domain Boundaries in Barium Titanate with High Angle Annular Dark Field(HAADF) Imaging

BaTiO3 have been studied for years by electron microscopists. Those studies have revealed the existence of 90° and 180° ferroelectric domain boundaries. The high angle annular dark field(HAADF) STEM technique is known to have strong sensitivity to atomic number Z. The signal is generated by the channelling of electrons along rows or planes and high angle scattering(mostly thermal diffuse scattering) from the atoms. Contrast in HAADF images can be given by crystal defects as a result of changes in channeling or changes in the high angle scattering process. This work reports a preliminary study of ferroelectric domain boundaries in BaTiO3 with HAADF imaging and a qualitative discussion of the observed domain wall contrast.

Three-dimensional transmission line model for flux conduction in thin-film recording heads

Flux spreading in thin-film recording heads has been studied using a three-dimensional transmission line model. This model uses the observed domain wall structure in a thin-film head as the map on to which a set of electrical circuit nodes in the model are placed. These nodes are connected in the transverse direction by inductive circuit elements which simulate the domain wall mobility for transverse flux conduction by wall motion. In the longitudinal direction skin-effect-limited conduction by magnetization rotation is simulated by a R/L series element. At frequencies above 8 MHz this model begins to exhibits a concentration of flux on the axis of the head.

Domain wall pinning by fine precipitates

The addition of Nb to the Nd-Fe-B-type magnet causes precipitates to form within the hard magnetic grain. Domain-wall pinning effects of the precipitates were investigated by measuring an initial magnetization curve and by domain-wall observation in a magnetic field using Lorentz microscopy. Precipitates which were 500 A in size and 10/sup 15/ nuclei/cm/sup 3/ in density were produced in an Nb-doped (Nd,Dy)-Fe-B sintered magnet and found to contain Nb. A Lorentz micrograph showed that the domain walls pass through the precipitates. The initial magnetization increased abruptly, which indicates that the magnetization process is still nucleation-type. It was observed that almost all walls disappear under application of an external field of 5 kOe. It is concluded that the pinning effect is not strong enough to produce a significant increase in the coercive force of the permanent magnet and that the suppression of grain growth by niobium addition is the cause of the improvement of the coercivity. >

Study of field-driven wall-configuration conversions for laminated Permalloy in the easy-axis state

Laminated Permalloy, with edge-curling walls replacing closure domains, has been proposed to increase permeability and reduce wall noise in recording. However, in structures meeting the criteria for Slonczewski’s ‘‘easy-axis’’ state, normal walls often coexist with edge-curling walls. We have used our laser magneto-optic microscope to study inductive-head-yoke shaped elements of two and four Permalloy layers separated by nonmagnetic, metallic spacers. In the four-magnetic-layer sample a state with a single wall, terminating at the edge-curling regions and lying along the easy-axis direction, is often observed on the top and bottom layers. Some elements may be driven into an easy-axis state with no observed domain walls. The two-magnetic-layer sample also exhibited simultaneous one-wall structures on the top and bottom layers. The other stable configuration was a no-wall state on the top layer and a two-wall (three-domain) state on the lower layer. These ‘‘coupled’’ states were exceptionally stable in both samples; fields on the order of 300 Oe were required to switch between configurations.

Experiment investigation of the ferroelastic domain structure in cesium lead chloride in the monoclinic phase

The experimental observations of the ferroelastic domain structure of CsPbCl3, in its monoclinic phase, are compared to the results obtained by a theoretical analysis using twinning by pseudo-symmetry, or a tensor method. The various kinds of observed domain walls are identified with the permissible W and S walls.

The variation of domain wall motion throughout the magnetization cycle in grain-oriented silicon-iron

The excess eddy current loss, formerly called the anomalous loss, is, in modern grain-oriented 3% silicon-iron, responsible for about 50% of the total loss for the power frequency range. Hence, it is commercially important for the causes of the excess eddy current loss to be defined. One of the suggested possible causes of the excess eddy current loss is non-sinusoidal, non-uniform and non-repetitive domain wall mobility from the ideal behaviour. In the study reported here, the domain wall positions have been measured in individual grains in commercial polycrystalline 3% grain-oriented silicon-iron for peak flux densities of up to 1.2 T and over a frequency range of 20 to 120 Hz. The flux density of the individual grain is maintained sinusoidal by the feedback technique and by restricting the peak flux density to 1.2 T the observed domain wall motions are completely repetitive. The domain wall motions have been observed using a double-sided stroboscopically illuminated Kerr magneto-optic effect bench which enables the domain structure, spacing and mobility, to be measured on both sides of the sample simultaneously. The position of the domain walls have been measured throughout the magnetization cycle. It is shown that the movement of the walls is not sinusoidal, although the localised flux density is sinusoidal. It is also shown that the wall motions are complex since the amount of domain wall bowing varies throughout the magnetization cycle.

Domain structures in orthorhombic KNbO3 and characterisation of single domain crystals

Domain configurations in large KNbO3 single crystals grown by a top seeded flux growth technique are studied by optical methods and etching techniques. The orientation of observed domain walls is consistent with the principles of mechanical compatibility and electrical neutrality. Experimental evidence for the existence of a new type of ferroelectric domain wall (S-wall) is presented. Miller indices of such walls are irrational and depend on spontaneous strain tensor coefficients. The preparation of large single domain crystals (up to 1/3 cm3) is described. Assessment of crystal perfection by x-ray topographic and interference methods reveals a very small mosaic spread (one minute of arc) and a good optical homogeneity.