Stripe Axis Research Articles

Spin waves excitation at micron-sized, anisotropy modified regions in amorphous Fe80B20 stripes: Local properties and inter-regions coupling

We report on the measurement of the local magnetization dynamics occurring, at units of GHz, in large aspect ratio stripes lithographed from reduced damping amorphous Fe80B20 films. The stripes were submitted to local anisotropy modifications by micrometric beam synchrotron X-ray irradiation. Our results include data on the dispersion relationships and group velocities corresponding to spin waves excited at both the non-irradiated and the irradiated regions. Whereas in the former case we observed standing spin waves with transverse-to-the stripe axis wave vector, in the latter one, for which the wave vector of the spin waves was parallel-to-the stripe axis, propagating spin waves were excited. In both regions, we measured the effective propagation distance of the spin waves, which resulted to be independent of the wave vector orientation. In the spin waves excited at the irradiated region, we also measured the decay time and effective damping coefficient, which was in good agreement with previously reported values obtained from FMR measurements in amorphous Fe80B20 continuous films. We show that the interaction of the non-irradiated and irradiated zones results, at the stripe transverse saturation remanence and under an exciting field frequency of 4 GHz, in the introduction of a π phase shift between the standing spin waves excited at both sides of the irradiated region. This result opens the possibility of using the local, transverse to the stripe axis, magnetic anisotropy easy axis induced by the X-ray irradiation as a crucial constituent of a zero-applied field spin wave phase-shifter.

Influence of Structural Defects on the Resistivity and Current Flow Field in Conductive Thin Layers

The paper presents an analysis of the influence of microcracks in textronic conductive layers on their conductive properties. The tested structures were created in the physical vacuum deposition process. The paper presents the results of computer simulations of the current flow field in thin conductive stripes with defects distributed along a line perpendicular to the stripe axis and randomly placed on its entire surface. It was found, inter alia, that a larger number of shorter collinear defects may have many times lower resistance than a small number of longer defects of the same total length (e.g., with 40 collinear cracks with a total length of 90% of the strip width, the sheet resistance is only about 3% greater compared to a track without cracks). It was found that the percolation threshold of the tested models with square proportions and randomly selected defects is close to the value of 0.5. This is consistent with the theoretical calculations for analogous discrete models with infinite sizes. It was also found that the sheet resistance of the conductive strip with randomly distributed defects clearly depends on its length when the defect concentration exceeds 20%. The simulations were carried out on the basis of the integral equation method, with the solution presented in the form of double layer potentials.

Unidirectional tilt of domain walls in equilibrium in biaxial stripes with Dzyaloshinskii–Moriya interaction

The orientation of a chiral magnetic domain wall in a racetrack determines its dynamical properties. In equilibrium, magnetic domain walls are expected to be oriented perpendicular to the stripe axis. We demonstrate the appearance of a unidirectional domain wall tilt in out-of-plane magnetized stripes with biaxial anisotropy and Dzyaloshinskii–Moriya interaction (DMI). The tilt is a result of the interplay between the in-plane easy-axis anisotropy and DMI. We show that the additional anisotropy and DMI prefer different domain wall structure: anisotropy links the magnetization azimuthal angle inside the domain wall with the anisotropy direction in contrast to DMI, which prefers the magnetization perpendicular to the domain wall. Their balance with the energy gain due to domain wall extension defines the equilibrium magnetization the domain wall tilting. We demonstrate that the Walker field and the corresponding Walker velocity of the domain wall can be enhanced in the system supporting tilted walls.

A comparison of the twisted and untwisted structures for one-dimensional carbon nanotube assemblies

The way how carbon nanotubes (CNTs) are assembled together determines the utilization efficiency of mechanical property in their macroscopic assembly materials. For one-dimensional (1D) assemblies, CNTs are often assembled under drawing and twisting into a fiber structure with a twist angle. In this study, an untwisted 1D assembly, CNT strip, is introduced, inside which the CNTs are not only aligned but also overall parallel to strip axis. Due to the shielding effect of the twisted fiber surface, the interior of CNT fiber is loosely packed, and the fiber is more stretchable and hard to become stiff. On the contrary, CNT strip with high straightness or undirectionality can utilize the CNT's mechanical property much more efficiently, as reflected by its higher strength and modulus. These insights can guide different applications of CNT fibers and strips in textile.

Polarized surface-enhanced Raman spectroscopy of suspended carbon nanotubes by Pt-Re nanoantennas

We present optical nanoantennas designed for applications that require processing temperatures larger than 800{\deg}C. The antennas consist of arrays of Re/Pt bilayer strips fabricated with a lift-off-free technique on top of etched trenches. Reflectance measurements show a clear plasmonic resonance at approximately 670 nm for light polarized orthogonal to the strip axis. The functionality of the antennas is demonstrated by growing single-walled carbon nanotubes (CNTs) on top of the antenna arrays and measuring the corresponding Raman signal enhancement of individual CNTs. The results of the measurements are quantitatively discussed in light of numerical simulations which highlight the impact of the substrate.

Ion irradiation effects on a magnetic Si/Ni/Si trilayer and lateral magnetic–nonmagnetic multistrip patterning by focused ion beam

Fabrication of a multistrip magnetic/nonmagnetic structure in a thin sandwiched Ni layer [Si(5 nm)/Ni(15 nm)/Si] by a focused ion beam (FIB) irradiation has been attempted. A control experiment was initially performed by irradiation with a standard 30 keV Ga ion beam at various fluences. Analyses were carried out by Rutherford backscattering spectrometry, X-ray reflectivity, magnetooptical Kerr effect (MOKE) measurements and MOKE microscopy. With increasing ion fluence, the coercivity as well as Kerr rotation decreases. A threshold ion fluence has been identified, where ferromagnetism of the Ni layer is lost at room temperature and due to Si incorporation into the Ni layer, a Ni0.68Si0.32 alloy layer is formed. This fluence was used in FIB irradiation of parallel 50 nm wide stripes, leaving 1 µm wide unirradiated stripes in between. MOKE microscopy on this FIB-patterned sample has revealed interacting magnetic domains across several stripes. Considering shape anisotropy effects, which would favour an alignment of magnetization parallel to the stripe axis, the opposite behaviour is observed. Magneto-elastic effects introducing a stress-induced anisotropy component oriented perpendicular to the stripe axis are the most plausible explanation for the observed behaviour.

Angular dependence of current-driven chiral walls

The current-driven dynamics of chiral domain walls is theoretically studied by means of realistic micromagnetic simulations. Trains of current pulses flowing through the heavy metal underneath the ferromagnetic layer are injected with different directions with respect to the ferromagnetic strip axis. The wall displacement is highly sensitive to the wall configuration and to the angle between the current and the longitudinal axis of the strip. These simulations can account for the experimental behavior at large currents, but preliminary results at lower current density point towards incompatibilities between the model and the experiment that need further experimental and theoretical efforts.

Domain wall dynamics of periodic magnetic domain patterns in Co2MnGe-Heusler microstripes

Highly symmetric periodic domain patterns were obtained in Co2MnGe-Heusler microstripes as a result of the competition between growth-induced in-plane magnetic anisotropy and shape anisotropy. Zero field magnetic configurations and magnetic field-induced domain wall (DW) motion were studied by magnetic force microscopy-image technique for two different cases: dominant uniaxial- and dominant cubic in-plane anisotropy. We implemented a magneto-optical Kerr effect susceptometer to investigate the DW dynamics of periodic domain structures by measuring the in-phase and out-of-phase components of the Kerr signal as a function of magnetic field frequency and amplitude. The DW dynamics for fields applied transversally to the long stripe axis was found to be dominated by viscous slide motion. We used the inherent symmetry/periodicity properties of the magnetic domain structure to fit the experimental results with a theoretical model allowing to extract the DW mobility for the case of transverse DWs (μTDW = 1.1 m s−1 Oe−1) as well as for vortex-like DWs (μVDW = 8.7 m s−1 Oe−1). Internal spin structure transformations may cause a reduction of DW mobility in TDWs as observed by OMMFF simulations.

In-plane rotation of magnetic stripe domains inFe1−xGaxthin films

The in-plane rotation of magnetic stripe domains in a 65-nm magnetostrictive ${\mathrm{Fe}}_{0.8}{\mathrm{Ga}}_{0.2}$ epitaxial film was investigated combining magnetic force microscopy, vibration sample magnetometry, and x-ray resonant magnetic scattering measurements. We analyzed the behavior of the stripe pattern under the application of a bias magnetic field along the in-plane direction perpendicular to the stripe axis, and made a comparison with the analogous behavior at remanence. The experimental results have been explained by means of micromagnetic simulations, supported by energy balance considerations. Fields smaller than $\ensuremath{\sim}400$ Oe do not induce any stripe rotation; rather, a deformation of the closure domains pattern was evidenced. Larger fields produce a sudden rotation of the stripe structure.

Néel walls between tailored parallel-stripe domains in IrMn/CoFe exchange bias layers

Tailored parallel-stripe magnetic domains with antiparallel magnetizations in adjacent domains along the long stripe axis have been fabricated in an IrMn/CoFe Exchange Bias thin film system by 10 keV He+-ion bombardment induced magnetic patterning. Domain walls between these domains are of Néel type and asymmetric as they separate domains of different anisotropies. X-ray magnetic circular dichroism asymmetry images were obtained by x-ray photoelectron emission microscopy at the Co/Fe L3 edges at the synchrotron radiation source BESSY II. They revealed Néel-wall tail widths of 1 μm in agreement with the results of a model that was modified in order to describe such walls. Similarly obtained domain core widths show a discrepancy to values estimated from the model, but could be explained by experimental broadening. The rotation senses in adjacent walls were determined, yielding unwinding domain walls with non-interacting walls in this layer system.

Effect of an electric field on the properties of BN Möbius stripes

In the present work, we present a first-principles study on the effects of an external electric field on the structural stability and electronic properties of boron nitride Möbius stripes with armchair and zigzag chirality. The calculation results indicate that the gap energy can be remarkably reduced by the application of an external field. Such reduction is in principle attributed to the occurrence of Stark effect, which significance depends on the orientation of the applied field relative to the stripe axis. Moreover, the electric field produces significant changes on dipole momentum of the structure and induces a negative shift on the calculated total energy, reducing the obtained formation energy.

OS0905 焼結体に圧延加工を加えて作製した傾斜機能形状記憶合金の変形特性

The martensitic and reverse transformation temperatures of TiNi shape memory alloy (SMA) are directly related to its bending rigidity. In this study, we developed a new fabrication process that combines powder metallurgy and plastic working to obtain a functionally graded TiNi SMA stripe that varies in bending rigidity from high to low along the stripe axis. First, a multilayered TiNi green compact in which the Ti-Ni compositions varied layer by layer was sintered using a spark plasma sintering process; the compact was then hot and cold rolled into stripes. We investigated the functionally graded properties of the local deformation properties of the resulting rolled thin stripes. Using stripes that already exhibit functionally graded properties, we observed that the transformation temperatures of hot- and cold-rolled TiNi SMA stripes are also functionally graded. As a result, the deformation behaviors of the rolled stripes differ depending on the Ni content at a given position.

Electronic and Magnetic Properties of Graphene M?bius Strips: Density Functional Theory Approach

Electronic and magnetic properties of graphene Mobius strips with different widths are studied using density functional theory. It is shown that the multiplicity of the Mobius strip, the cohesive energy, and the band gap energy increase with increasing the width of Mobius strip. We show that the magnetic moment of Mobius strip decreases with increasing the curvature and strain. Then the effects of an external electric field applied in the direction of the Mobius strip axis are studied and it is found that the Mobius strip keeps its metallic surface (edge) states even in the presence of the electric field. For sufficiently high applied electric field, the spin-flipping can take place in the Mobius strip. In addition, in contrast with the graphene nanoribbons, the graphene Mobius strips show half-semiconducting properties when an external electric field is applied.

Growth of magnetic nanowires on self-organized stripe templates: Fe on Pd–O/W(110)

The structural and magnetic properties of Fe-Pd nanostructures grown on regular alternating Pd and oxygen stripes on the W(110) surface are studied using SPELEEM methods. The self-organized Pd-O stripe template, formed at about 1000 °C and aligned with the [001] direction, has an average period of only few tens nm and is preserved upon quenching the sample temperature to ambient conditions. Fe is shown to preferentially bond to the Pd stripes, forming an Fe-Pd surface alloy within the stripe phase. The magnetic easy axis is found to be aligned perpendicular to the Fe-Pd stripe axis.

Magnetic domain patterns in Co2MnGe Heusler nanostripes

We have prepared thin films of the ferromagnetic Heusler alloy Co2MnGe on a-plane Al2O3 substrates exhibiting growth-induced, superimposed fourfold and uniaxial magnetic anisotropies, the symmetry being determined by the single-crystalline Al2O3 substrate. The magnitude of the uniaxial anisotropy compared to the cubic anisotropy can be tuned over a wide range by the film thickness and the growth conditions. On submicrometer-wide stripes of Co2MnGe prepared by electron beam lithography we studied magnetic domain patterns by magnetic force microscopy. For stripes with a sufficiently large uniaxial anisotropy and with the easy axis oriented perpendicular to the stripe axis, we find perfectly regular domain patterns with the magnetization direction perpendicular to the stripe axis and alternating from domain to domain. The highly regular and controllable domain patterns in Co2MnGe nanostripes could be useful for magnetic storage devices and applications related to spin transfer torque.

Spin-wave damping in ferromagnetic stripes with inhomogeneous magnetization

A theory is presented for the interactions between the dipole-exchange spin waves in ferromagnetic nanowires with a stripe geometry. A Hamiltonian-based approach is used in order to extend earlier results for the linear (or noninteracting) spin waves to include the leading nonlinear processes due to three-magnon and four-magnon effects in a stripe. As well as the magnetic dipole-dipole and exchange terms in the Hamiltonian, the role of an applied magnetic field that can be either parallel or perpendicular to the stripe axis is considered. Within a diagrammatic perturbation method the contributions to the frequency shift and damping of the quantized spin waves are deduced. Numerical calculations are presented for Permalloy stripes, and it is shown that the damping in the transverse field case, where the magnetization may become strongly inhomogeneous, can be larger than that in the longitudinal field case. Comparisons are made with recent damping measurements for Permalloy stripes in a longitudinal field.

Polarized neutron studies on exchange-bias micro-stripe pattern

In the present study we examined the results of competing interactions in laterally exchange biased modulated thin films. For studying the magnetic interactions between neighboring magnetic elements we designed a model system. Considering that the model system should be of technological interest on the one hand, and should allow the application of several different and efficient experimental techniques for complementary analysis on the other hand, we have chosen films with in-plane stripe-like magnetic domains. The evolution of the magnetic domain structure along the hysteresis loop was analyzed with a combination of experimental techniques: magneto-optical Kerr effect, Kerr microscopy, polarized neutron reflectometry, and off-specular scattering of polarized neutrons with polarization analysis.Due to the competition between interfacial exchange bias at the ferromagnetic-antiferromagnetic interface and intra-layer exchange interactions between neighboring ferromagnetic stripes the alignment is not perfectly antiparallel, but is periodically canted with respect to the stripe axis. Thus the net magnetization of the ferromagnetic film turns almost perpendicular to the stripes. At the same time the projection of the magnetization vector onto the stripe axis has a periodically alternating sign. The experimental observations are explained and quantitatively described within the frame of a phenomenological model. The model defines conditions which can be used for tailoring nano- and micro-patterned EB systems with different types of magnetic order.

Competing magnetic interactions in exchange-bias-modulated films

The magnetization reversal in stripelike exchange-bias-patterned ${\text{Ni}}_{81}{\text{Fe}}_{19}/\text{IrMn}$ thin films was investigated by complementary inductive and high-resolution magneto-optical magnetometry, magneto-optical Kerr microscopy, and polarized neutron reflectometry to clarify the effects of competing interfacial exchange-bias and lateral interface contributions. Structures of varying ferromagnetic layer thickness and stripe period were analyzed systematically at the frozen-in domain state of oppositely aligned stripe magnetization. For all samples the mean magnetization of the magnetic hybrid structures was found to be aligned nearly orthogonally with respect to the stripe axis and the set exchange-bias direction. Due to the interaction of interfacial coupling, exchange, and magnetostatic energy contributions, the opening angle of neighboring stripe magnetizations increases with decreasing ferromagnetic layer thickness and increasing stripe period. The experimental observations are in agreement with an earlier proposed model for designing micropatterned exchange-bias films.

High-Qplasmonic resonators based on metal split nanocylinders

In this paper we report on a detailed investigation of the quality $Q$ factor exhibited by metal-nanostrip resonators with a bent axis. A detailed comparison of the $Q$ with the quasistatic limit value demonstrates that under a large bending of the strip axis the resulting split-cylinder nanoresonators exhibit a $Q$ that is exceeding the quasistatic $Q$ in the near infrared. Also, a possible application of high-$Q$ split-cylinder nanoresonators as high-sensitive plasmonic sensors is proposed.

The Topography of Microstructured Surfaces Differently Affects Fibrillin Deposition by Blood and Lymphatic Endothelial Cells in Culture

While tissue-engineered blood vessels have already been successfully used in surgical practice, artificially restoring lymphatic circulation when needed is still far to be realized. Stability of arterial vessel wall depends on proper fibrillin deposition; fibrillin in fact is the scaffold for elastic fiber formation. In lymphatic vessels fibrillin is probably implied in lymph formation in response to interstitial requirements. This study was designed to verify whether fibrillin deposition is influenced by the topography of the substrate on which blood and lymphatic endothelial cells grow. Blood and lymphatic endothelial cells were cultured on microstructured surfaces with different topography: stripes of different widths (25, 50, and 100 microm), squares and rectangles, and spiral geometry, obtained by the photoimmobilization of Hyaluronan (Hyal) on aminosilanized glass. Cell orientation and fibrillin deposition were influenced by the topography of the microstructure. Blood endothelial cells deposited fibrillin as a bundle running parallel to the major axis of stripes and spirals, whereas the irregular network of fibrillin deposited by lymphatic endothelial cells was affected by the topography of the substrate only in the smallest stripes. These data bring a contribution to the basic knowledge required to design tissue-engineered blood and lymphatic vessels capable of adapting to the functional requirements of the surrounding environment.