Stripe Domain Pattern Research Articles

Reorientational magnetic transition in mesoscopic cobalt dots

We have measured magnetic anisotropy constants and domain structures in arrays of magnetic dots 0.5 μm wide fabricated out of an epitaxial (0001) hcp cobalt film. Occurrence of a concentric stripe domain pattern for which the magnetization is mostly in-plane with small alternately up and down perpendicular components is found for a 25-nm-thick cobalt dot array. Interestingly, this sample produces a spin reorientation from a quasi in-plane to a fully perpendicularly oriented magnetization when the temperature is lowered, due to an increase of the perpendicular anisotropy at low temperature.

Free-standing mesoporous silica films; morphogenesis of channel and surface patterns

Extraordinary channel patterns have been observed in an oriented mesoporous silica film that is synthesized at the boundary between air and water. The basic channel designs comprise concentric circles, herringbones, fingerprints and hairpins. It is suggested that these patterns are spatio-temporal silicified recordings of the polymerization and growth of a silicate liquid-crystal seed emerging in two spatial dimensions at the air/water interface. The origin of the channel patterns may be from defects, such as disclinations and dislocations, that spontaneously form in a surface confined precursor silicate liquid-crystal film to give a liquid-crystalline texture to the resulting mesoporous silica film. The reaction–diffusion processes and defects that are believed to contribute to the curved three-dimensional morphologies and channel patterns of mesoporous silica free to grow in solution, may also occur in the surface version, except that the isotropy of solution is replaced by the anisotropy of the air/water interface together with proximity effects from neighboring growth centers. Polymerization induced radial stresses produced in the as-synthesized mesoporous silica film before drying, are relieved through warping of the film into micrometer-scale hillock-shaped protuberances. These mounds are arranged into patterns that appear to reflect the channel designs within the film. A linear radial stress model is found to successfully account for the warp patterns. A possible connection between the two-dimensional channel patterns in mesoporous silica films and the two-dimensional stripe domain patterns found in modulated phases is discussed.

Domain structure of iron single crystals grown on Si(111) investigated by magnetic force microscopy (abstract)

Single-crystal iron films grown epitaxially on (111) silicon were studied using a magnetic force microscope (MFM). The crystalline anisotropy easy axes (〈100〉), directed 35° out of the film plane, result in a significant magnetic charge density at the film surface and a sixfold symmetry in the energy minima of the system. To reduce the magnetostatic energy of this configuration, an alternating, stripe domain pattern formed in samples of thickness ranging from 1240 to 315 nm. Because of the wavelike form of the MFM response across the stripes, two-dimensional Fourier transforms of the MFM images were used to give measures at the domain period, i.e., the wavelength of the stripes, as well as the complexity of the patterns. The stripe domain period was found to be approximately equal to the film thickness which is consistent with previous theoretical predictions. The domain patterns of the films in various remanent states and progressive stages of the magnetization process were investigated using the MFM and an in situ, variable magnetic field. A MFM tip that is magnetically soft compared to the iron is most suitable for this. Measurements of the domain period and pattern complexity as a funciton of applied field were correlated with bulk hysteresis measurements.

一方向性けい素鋼板の圧縮応力下における磁区構造変化

The effects of compressive stress on the magnetization in grain-oriented silicon iron sheets have been investigated. The magnetization changes due to compression are composed of two effects, reversible and irreversible magnetization changes. The magnetization changes due to compression for a sample cut at a declining angle of 35° from the rolling direction have peculiar characteristics. This sample shows two peaks of magnetization change due to compression. Changes in the domain structure due to compression were observed in order to determine the mechanism of magnetization change. A stripe domain pattern with 180° domain walls changes into a small perpendicular stripe pattern as a result of the application of both a magnetic field and compression, and the density of stripes changes as a result of compressive stress.

Pattern analysis of magnetic stripe domains morphology and topological defects in the disordered state

Abstract A direct-space analysis of globally disordered (‘labyrinthine’) stripe domain patterns in thin ferrimagnetic garnet films is presented. A set of algorithms, designed to encode and analyse line patterns, serves to identify and correlate the positions of topological defects, and to delineate structural motifs in the pattern morphology. Despite the fact that labyrinthine patterns represent a metastable state, statistical analysis of morphological and certain geometrical features extracted via pattern analysis reveals that the labyrinthine state's structure is well defined and robust; it is composed of oblong polygonal regions of ‘smectic’ ordering of its constituent line segments. That is, there exists a well defined length scale in these globally disordered labyrinths over which the ordered lamellar state of minimal free energy is realized; this length scale corresponds to a characteristic size of the ordered regions (‘segment clusters’). Furthermore, local orientational correlations of adjacent se...

Ion beam sputter deposited Permalloy thin films

Ni/sub 80/Fe/sub 20/ thin films were deposited using a wide range of process parameters in a dual source ion beam sputter deposition system. The films were characterized structurally, chemically, and magnetically. Two modes of deposition were investigated; the first permitted concurrent second source bombardment during film deposition but was limited in net deposition rate to about 300 AA/m; the second provided deposition rates in excess of 1000 AA/m, but did not allow for concurrent ion bombardment from the second ion source. Depending on specific conditions film stress varied from slightly tensile to highly compressive in both deposition modes. This, combined with small variations in magnetostriction, resulted in films with vertical anisotropy and stripe domain patterns as well as conditions where well-formed closure domain patterns were observed in yoke shaped structures. For monolithic films, easy axis coercivities >

Magnetic characterization of ion-beam sputter deposited permalloy thin films

Ni 80Fe 20 thin films were deposited using a wide range of process parameters in a dual source ion-beam sputter deposition system. The films were characterized magnetically, structurally and chemically. Depending on specific deposition conditions, film stress varied from slightly tensile to highly compressive in both deposition modes. This combined with small variations in magnetostriction resulted in films with vertical anisotropy and stripe domain patterns as well as conditions where well formed closure domain patterns were observed in yoke-shaped structures. For the monolithic films, easy-axis coercivities of < 0.7 Oe, anisotropy fields of ≅ 4 Oe and hard-axis coercivities of < 0.5 Oe were obtained.

Morphology and Local Structure in Labyrinthine Stripe Domain Phase

Analysis of globally disordered, nonequilibrium "labyrinthine" stripe-domain patterns in thin ferrimagnetic garnet films has revealed a well-defined local structure containing an oblong polygonal plaquette as the fundamental motif. Two types of labyrinths were found: one having topological defects, the other composed of a single, unbranched, meandering line. These patterns emerge when the labyrinthine state is approached either by heating at constant magnetic field or by demagnetizing from saturation at constant temperature. Size and aspect ratios of the oblong polygonal plaquettes prove to be independent of the choice of these two mutually orthogonal trajectories within the phase diagram, which is surprising in view of the different mechanisms and concomitant topological constraints governing the evolution of disorder. The significance of this unique local structure is discussed in the general context of defectmediated melting of two-dimensional stripe phases.

Strong stripe domains in 80Co 20Ni obliquely deposited films

Obliquely deposited cobalt-nickel films were studied as continuous magnetic media. The columns are sufficiently in contact to produce effectively a continuous magnetic layer. For film thicknesses below about 800 AA, relatively wide in-plane domains are observed which may give rise to unfavorable zigzag walls. Beyond a critical thickness of about 800 AA, a regular, globally nonmagnetic strong stripe-domain pattern takes over, which should be a favourable information carrier. The domain width for these patterns increases with the film thickness. Films just beyond the critical thickness are therefore expected to be the best choice from the standpoint of magnetic microstructure. In these films a modulation of the strong stripe pattern should allow a continuous magnetization transition in longitudinal recording as in particulate media, avoiding the irregular zigzag transition characteristic of conventional thin-film media.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Flux Reversal and Calculations of Hysteresis Loops in CoCr Sputtered Films

Stripe domain patterns were clearly observed in CoCr-sputtered films using the Bitter method. These patterns suggested that wall motion dominates the flux reversal for films having a low coercive field; however, both the wall motion and rotational modes take place in a flux reversal for films having a high coercive field. Therefore, the hysteresis loops and angular dependence of the coercive field for CoCr sputtered films were calculated based on the assumption of a simultaneous occurrence of the rotational and wall motion modes. Good agreements were obtained between the experimental and calculated results.

Thermal, magnetic and magnetomechanical properties of amorphous magnetron sputtered Fe&amp;lt;inf&amp;gt;78&amp;lt;/inf&amp;gt;B&amp;lt;inf&amp;gt;13&amp;lt;/inf&amp;gt;Si&amp;lt;inf&amp;gt;9&amp;lt;/inf&amp;gt;

Large scale thick films of a high coupling magnetostrictive metallic glass have, for the first time, been successfully produced by magnetron sputtering and removed from the substrate. Magnetization and coupling factor experiments were performed on these free-standing films. Annealing of the samples resulted in a coercive force an order of magnitude lower than that achieved thus far by RF sputtering. Values of 35 mOe coercive force and 0.74 coupling factor were obtained. SEM pictures show the presence of a striped domain pattern distorted by the presence of residual inhomogeneous stresses.

Stability of domain patterns and domain wall coercivity

The stability of demagnetized stripe domain patterns of epitaxial magnetic garnets with respect to applied field pulses has been observed to be strongly dependent on the magnetic history of the sample. The highest stability with regard to irreversible changes of the wall positions has been measured after the demagnetization by a slowly decreasing ac field normal to the specimen which is commonly considered to yield the lowest total energy domain structure with the zero field stripe period. In such a case the stability field has been found just equal to the sample's coercivity. The measurement is believed to make it possible to decide experimentally which of the alternative domain structures of a certain type is the lowest energy one.

Structure-sensitive magnetic properties of RF sputtered NiFe films

X-ray small angle scattering (SAS) and transmission electron microscopy (TEM), together with MH loop measurements, were used to investigate effects of substrate bias on microstructural and magnetic anisotropy of sputtered NiFe films of 80-81 wt.% Ni. Films of ∼4000Å thickness had perpendicular anisotropy H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> ∼210 Oe when prepared with 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> Torr base pressure and without bias, but MH loops showed no evidence of perpendicular anisotropy for bias voltages of -60V or more. SAS for these films correlated closely with values of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> , being intense and anisotropic for 0V bias films but very weak for films sputtered with -60V or -120V bias. This correlation suggests that substrate bias for sputtered films and substrate temperature for evaporated films have similar effects on microstructure and magnetic anisotropy and that the magnetic anisotropy arises from magnetostatic interactions at aligned, crack-like voids. TEM observations were limited to films of 300Å-1300Å thickness. A strong void network and stripe domain pattern were seen only for 0V bias films prepared in poor vacuum. Improved vacuum conditions or application of -120V bias produced much more homogeneous films having in-plane domain structures for this range of thicknesses.

Excitation of stripe domain patterns by propagating acoustic waves in an oriented nematic film

Stripe domain patterns have been observed in a nematic liquid crystal film excited by ultrasonic waves propagating in a sandwiched glass-nematic-glass medium. The effect was found to be due to molecular reorientation induced by acoustic streaming in the nematic film. Based on a simple fluid dynamical model, we calculated the propagating acoustic modes, their nonlinear mixing which causes acoustic streaming, and the resultant shear flow reorientation of the director which produces the birefringent stripe patterns. Our calculations show quantitative agreement with the measured acoustic modes and the observed stripe domain patterns.

Temperature dependence of power loss anomalies in directional FeSi 3%

Measurements as a function of temperature t were performed on directional FeSi 3%, in order to study the possible influence on the power loss anomalies of a change of intrinsic parameters, such as crystalline anisotropy energy K, without affecting the extrinsic ones, such as grain size and orientation. Power losses per cycle P/f were measured vs. frequency f, between d. c. and 50 Hz at various temperatures ranging from 25 to 650°C. The variation of K and of saturation induction B s with t were also determined up to the Curie point by means of a torque magnetometer. The results show that the excess loss anomaly at 50 Hz, measured by the ratio of experimental to classical eddy-current loss, and the non-linearity anomaly, determined from the renormalized P/f vs. f curves, are essentially independent of t. Analogies with the temperature dependence of the power density spectrum of the Barkhausen noise, which varies according to a B_{s}^{2} (t) law, are briefly discussed. These results seem to indirectly stress the role of extrinsic parameters in determining the anomalous loss behaviors in directional FeSi 3%. Kerr observations made up to 350°C on a (300 × 30)mm2strip did not detect any change of stripe domain widths and patterns.

Bubble lattice formation in thick MnBi platelet by one-point nucleation

The dynamic domain formations in a single crystal MnBi platelet were examined under various external field strengths. Once the reverse domain is nucleated at one point of the saturated plate by pricking or external pulse field, the domain expands with various modes depending on the net field strength acting on the moving wall and forms various patterns. In a thick platelet, a bubble lattice is produced with no bias field, but it is suppressed by the external field; a radial stripe domain pattern or a spider web like pattern is formed depending on the field polarity. The phase velocity of the wall propagation during lattice formation was estimated as about 50m/sec by the pulse field method. This result brought us the important information about the truly complicated nature of the bubble lattice formation, i.e., the sequential process of the dynamic conversion, breakdown of velocity, static conversion, high speed propagation, and sharp deflection.

Electro-optic effects in smectic C liquid crystals

Electro-optic effects are observed in the smectic C states of 4- n-heptyloxybenzoic acid, 4- n-octyloxybenzoic acid. 4,4′-bis- n-heptyloxyazoxybenzene, and 4- n-decyloxy cinnamic acid under the application of an external ac electric field. The stripe domain pattern is observed for all the compounds studied above the first threshold. In the smectic C state there exists a second threshold at which the direction of the domain lines changes.

Magnetic domains in (Gd0.5Y2.5)(Ga1Fe4)O12 garnet films

We present a model which explains the behavior of the magnetization and the resultant stripe domain patterns in thin films of (Gd0.5Y2.5) (Ga1Fe4)O12 grown by liquid-phase epitaxy on [111]-oriented GGG substrates under the influence of dc or pulsed in-plane magnetic fields.

New method to determine the domain wall energy in thin uniaxial films with perpendicular easy axis and large saturation magnetization

The surface energy density, γ, of domain walls in thin uniaxial films with perpendicular easy axis is usually found either by measurements of the domain pattern period of the stripe domain pattern or by determination of the bubble collapse field and diameter. However, when the saturation magnetization is large, the widths of stripe domains and bubbles become smaller than the minimum optical resolution, and optical observation becomes impossible. The method proposed in this paper is based on measurements of the susceptibility S = d ( M/M s)/d( H a/4π M s) of the stripe pattern at M = 0. Optical observations are avoided. The only additional important quantities are the saturation magnetization M s and the film thickness. The method has been successfully applied to MnBi films ( M s = 625 G). The determination of γ in this material yields γ = (15 ± 1) erg/cm 2.

Analysis of a method for measuring the magnetocrystalline anisotropy of bubble materials

A method of measuring the uniaxial anisotropy of bubble materials is analyzed. The method consists of observing the in-plane field H∥* at which a stripe domain pattern disappears. Calculations, based on a model with uniaxial anisotropy, are presented which give a relation between H∥* and the uniaxial anisotropy field HK for different values of the characteristic magnetic length. It is shown that H∥* is always smaller than HK owing to the influence of the wall energy and the demagnetizing energy. The calculations are verified experimentally.