Out Of Plane Component Research Articles

Out-of-plane Emission Dipole of Second Harmonic Generation in Odd- and Even-layered vdWs Janus Nb3SeI7.

Integration of atomically thin nonlinear optical (NLO) devices demands an out-of-plane (OP) emission dipole of second harmonic generation (SHG) to enhance the spontaneous emission for nanophotonics. However, the research on van der Waals (vdWs) materials with an OP emission dipole of SHG is still in its infancy. Here, by coupling back focal plane (BFP) imaging with numerical simulations and density functional theory (DFT) calculations, we demonstrate that vdWs Janus Nb3SeI7, ranging from bulk to the monolayer limit, exhibits a dominant OP emission dipole of SHG owing to the breaking of the OP symmetry. Explicitly, even-layered Nb3SeI7 with C6v symmetry is predicted to exhibit a pure OP emission dipole attributed to the only second-order susceptibility coefficient χzxx. Meanwhile, although odd-layered Nb3SeI7 with C3v symmetry has both OP and IP dipole components (χzxx and χyyy), the value of χzxx is 1 order of magnitude greater than that of χyyy, leading to an approximate OP emission dipole of SHG. Moreover, the crystal symmetry and OP emission dipole can be preserved under hydrostatic pressure, accompanied by the enhanced χzxx and the resulting 3-fold increase in SHG intensity. The reported stable OP dipole in 2D vdWs Nb3SeI7 can facilitate the rapid development of chip-integrated NLO devices.

Tuning the spin of Dirac fermions on the surface of topological insulators in proximity to a helical spin density wave

We investigate the spin tunability of Dirac fermions on the surface of a 3D topological insulator in proximity to a helical spin density wave, acting as an applied one-dimensional periodic potential for spins produced by spiral multiferroic oxide. It is observed that the spin mean values of Dirac fermion undergo oscillations under the influence of such a periodic potential created by the exchange field of magnetization. The tunability of spin is strongly affected by the strength, orientation and period of the exchange field. In particular, the mean values of spin are anisotropic around the Dirac point, depending strongly on the amplitude and spatial period of the periodic potential. We also find that the spin expectation values change significantly by changing the plane of magnetization. Interestingly, the in-plane components of spin mean values perform pronounced oscillations, whereas the out of plane component does not oscillate at all. The oscillations of planar components of spin are originated from the spin-momentum locking on the surface of topological insulator.

Interfacial coupling effect of Cr2O3 on the magnetic properties of Fe72Ga28 thin films

Here it is investigated the effect of the antiferromagnet Cr2O3 on the magnetic properties of ferromagnetic Fe72Ga28 thin films. Sputtered Fe72Ga28 layers have their magnetization in the sample plane with a magnetic fluctuation that gives rise to magnetic ripple. In order to turn its magnetization into the out of plane (OOP) direction, it has been magnetically coupled with Cr2O3 that has magnetic moments along the c-axis, that is the perpendicular direction when properly aligned. Cr2O3 has been obtained from Cr oxidation, whereas Fe72Ga28 has been deposited on top of it by sputtering in the ballistic regime. Although a uniaxial in-plane magnetic anisotropy is expected for Fe72Ga28 thickness above 100 nm, the interfacial coupling with Cr2O3 prevents this anisotropy. The formation of stripe domains in Fe72Ga28 above a critical thickness reveals the enhancement of the out of plane component of the Fe72Ga28 magnetization with respect to uncoupled layers. Due to the interface coupling, the Fe72Ga28 magnetization turns into the out-of-plane direction as its thickness is gradually reduced, and a perpendicular magnetic anisotropy of 3·106 erg·cm−3 is inferred from experimental results. Eventually, the coupling between Cr2O3 and Fe72Ga28 promotes an exchange-bias effect that has been well fitted by means of the random field model.

Mixing and scalar dissipation rate in a decaying jet

The temporal development of the mixing field in a decaying jet (Re = 50,000) was quantified by measuring mole fraction and scalar dissipation rate (SDR) in a decaying, isothermal, turbulent gaseous jet. The 2D scalar field was measured by using planar laser induced fluorescence of acetone and, with appropriate image processing, this allowed estimation of the SDR using the two in-plane components within 16% error. The instantaneous and averaged distributions of the mole fraction are reported for downstream dimensionless distances up to 7 nozzle exit diameters and 35 exit flow timescales after end of injection. With advection of the last uniform exit concentration (UEC) profile core away from the nozzle exit, a region of weak concentration arises at the decaying jet's trailing edge. Estimates made in a Lagrangian frame of reference show that the trailing edge of the jet becomes leaner, after the end of injection (AEI), faster than in the steady state, confirming the existence of an ‘entrainment wave’. The normalised probability density functions of the 2D SDR at various stations and times AEI differ from a lognormal distribution at both low and high SDR values with negative skewness and positive excess kurtosis. A pseudo 3D SDR, made by including an estimate for the out of plane component, showed reduced departure from lognormal. The departure may be attributed to the disappearance of the strong shear layer associated with the absence of nozzle momentum AEI. To the authors’ knowledge, this study provides the first measurements of the SDR in a decaying, isothermal turbulent jet.

Out of plane component of the magnetization of sputtered Fe72Ga28 layers

In this paper we present an investigation about the out of plane component of the magnetization of Ga-rich sputtered FeGa thin films. To study this magnetic component, we have used magnetometric measurements and magnetic force microscopy combined with a structural characterization by means of x-ray diffractometry. For a more profound analysis, we have examined samples in both, as-grown and annealed state. The out of plane component of the magnetization promotes a magnetic ripple observed by magnetic force microscopy in all the studied samples. To quantitatively monitor the out of plane component of the magnetization, we have used the ratio between the magnetic remanence and the maximum magnetization (Mr/Mmax), i.e. the squareness, measured in the perpendicular hysteresis loops. The experimental results indicate that the out of plane component of the magnetization is reduced upon annealing at a moderate temperature of 400 °C. The experimental results can be understood considering that phase coexistence is the most likely origin for the observed magnetic ripple.

Self-Consistent Two-Gap Approach in Studying Multi-Band Superconductivity of NdFeAsO0.65F0.35

High-quality single crystals of NdFeAsO$_{0.65}$F$_{0.35}$ (the transition temperature $T_{\rm c} \simeq 30.6$~K) were studied in zero-field (ZF) and transverse-field (TF) muon-spin rotation/relaxation ($\mu$SR) experiments. An upturn in muon-spin depolarization rate at $T\lesssim 3$~K was observed in ZF-$\mu$SR measurements and it was associated with the onset of ordering of Nd electronic moments. Measurements of the magnetic field penetration depth ($\lambda$) were performed in the TF geometry. By applying the external magnetic field $B_{\rm ex}$ parallel to the crystallographic $c$-axis ($B_{\rm ex}\| c$) and parallel to the $ab$-plane ($B_{\rm ex}\| ab$), the temperature dependencies of the in-plane component ($\lambda_{ab}^{-2}$) and the combination of the in-plane and the out of plane components ($\lambda_{ab,c}^{-2}$) of the superfluid density were determined, respectively. The out-of-plane superfluid density component ($\lambda_{c}^{-2}$) was further obtained by combining the results of $B_{\rm ex} \| c$ and $B_{\rm ex} \| {ab}$ set of experiments. The temperature dependencies of $\lambda_{ab}^{-2}$, $\lambda_{ab,c}^{-2}$, and $\lambda_{c}^{-2}$ were analyzed within the framework of a self-consistent two-gap model despite of using the traditional $\alpha$-model. Interband coupling was taken into account, instead of assuming it to be zero as it stated in the $\alpha$-model. A relatively small value of the interband coupling constant $\Lambda_{12} \simeq 0.01$ was obtained, thus indicating that the energy bands in NdFeAsO$_{0.65}$F$_{0.35}$ are only weakly coupled. In spite of their small magnitude, the coupling between the bands leads to the single value of the superconducting transition temperature $T_{\rm c}$.

Investigation of the Out of Plane Component of the Magnetization of [Fe72Ga28(x nm)/Tb33Fe67(50 nm)]2 Multilayers

In this work the authors present their investigation on sputtered [Fe72Ga28/Tb33Fe37]2 multilayers in which the Tb‐Fe thickness is kept fixed (50 nm), whereas the Fe‐Ga ranged from 25 to 100 nm. In particular, the authors have study the out of plane component of the magnetization by means of vibrating sample magnetometry and magnetic force microscopy. Samples are structurally characterized by X‐ray diffractometry and electron microscopy in order to correlate the magnetic characterization with the structural properties. In addition, the authors anneal the samples at 400 °C in order to analyze the effect of the thermal treatment on both, structural and magnetic properties. In the as‐grown samples, the out of plane component of the magnetization can be related to both, Tb‐Fe and Fe‐Ga. However, experimental results indicate that annealing reduces this component of the magnetization due to the crystallization of ordered phases in the Fe‐Ga layers.

Numerical analysis of frequency optimization and effect of liquid sodium for ultrasonic high frequency guided wave inspection of core support structure of fast breeder reactor

The paper discusses the numerical modeling of ultrasonic high frequency guided waves (HFGW) for nondestructive inspection of main vessel core support structure (MV-CSS) in sodium cooled prototype fast breeder reactor (PFBR). A series of 2D plain strain finite element (FE) models have been created by using an explicit scheme to optimize the transducer frequency for efficient generation of HFGW in MV-CSS. The time-frequency smoothed pseudo Wigner-Ville distribution (SPWVD) has been used to analyze the generated HFGW modes. With optimum transducer frequency, several FE models have been created with a reference defect down to 20% of 30 mm wall thickness (6 mm) on MV-CSS for analyzing the propagation behavior of HFGW under the influence of fluid loading (liquid sodium) boundary conditions at high temperature. The simulation results are validated by experimental measurements performed on a mock-up structure of the MV-CSS for frequencies in the range of 0.5–5 MHz. The amplitude response of HFGW is found to be maximum at 2.25 MHz and considerably non-dispersive. The model predictions are found to capture all features observed in the experiments. Most of the out of plane components of HFGW are leaked through the liquid sodium which in turn, affects the propagation characteristics of the guided waves in the MV-CSS. From the simulation results, it has been observed that the reference defect signal amplitude decreases with increasing temperature of liquid sodium.

Elucidation of the helical spin structure of FeAs

We present the results of resonant x-ray scattering measurements and electronic structure calculations on the monoarsenide FeAs. We elucidate details of the magnetic structure, showing the ratio of ellipticity of the spin helix is larger than previously thought, at 2.58(3), and reveal both a right-handed chirality and an out of plane component of the magnetic moments in the spin helix. We find that electronic structure calculations and analysis of the spin-orbit interaction are able to qualitatively account for this canting.

Magnetic field angle dependence of out-of-plane precession in spin torque oscillators having an in-plane magnetized free layer and a perpendicularly magnetized reference layer

Out-of-plane (OP) precession in spin torque oscillators having an in-plane (IP) magnetized free layer and a perpendicularly magnetized reference layer was studied. The bias voltage (VB) and magnetic field angle (θ) dependence of the OP precession were investigated. The absolute values of the critical magnetic fields ( and ) between which OP precession is excited increased as VB increased and as θ changed from the IP to the OP direction. The IP components of converged to a constant value regardless of θ. This result indicates that excitation of OP precession is suppressed entirely by the IP component of the magnetic field, and the contribution of the OP component can be ignored. The experimentally observed precession behavior was successfully modeled by macrospin simulations.

Tunable stress induced magnetic domain configuration in FePt thin films

We present a study of the magnetic properties of chemically disordered ferromagnetic FePt films of 100 nm thickness that have been grown by sputtering with different Ar pressures ( mTorr). We found that the residual stress can be controlled by the sputtering pressure, which in turn allows to tune the perpendicular magnetic anisotropy due to magnetoelastic effects. Films deposited at lower Ar pressures display an in-plane compressive stress that favors an out of plane component of the magnetization and the formation of a magnetic domain structure in the form of stripes. For higher pressures the stress is relaxed and the magnetic configuration changes to planar domains. These results show the possibility to accurately tune the initial magnetic state in films with potential applications in magnetoelectrically coupled devices.

Assessment of Damage Detection in Composite Structures Using 3D Vibrometry

Carbon fibre reinforced polymers (CFRP) have been used significantly more in recent years due to their increased specific strength over aluminium structures. One major area in which their use has grown is the aerospace industry where many now use CFRP in their construction. One major problem with CFRP's is their low resistance to impacts. Structural health monitoring (SHM) aims to continually monitor a structure throughout its entire life and can allow aircraft owners to identify impact damage as it occurs. This means that it can be repaired prior to growth, saving weight with the repair and the time that aircraft is grounded. Two areas of SHM being researched are Acoustic Emission (AE) monitoring and AcoustoUltrasonics (AU) both based on an understanding of the propagation of ultrasonic waves. 3D Scanning laser vibrometry was used to monitor the propagation of AU waves with the aim of gaining a better understanding their interaction with delamination in carbon fibre reinforced polymers. Three frequencies were exited with a PZT transducer and the received signal analysed by a cross correlation method. The results from this and the vibrometer scans revealed 100 kHz as the most effective propagating frequency of the three. A high resolution scan was then conducted at this frequency where it could be seen that only the out of plane component of the wave interacted with the damage, in particular the A0 mode. A 3D Fast Fourier Transform was then plotted, which identified the most effective frequency as 160 kHz.

Reactivity, aromaticity and absorption spectra of pillar[5]arene conformers: A DFT study

Reactivity and aromaticity of conformers of pillar[5]arene are discussed in the light of DFT and conceptual density functional theory. The absorption spectra of the conformers are analysed using TDDFT (time dependent density functional theory). Reactivity parameters, total electronic energy (Eel), energy of the HOMO (highest occupied molecular orbital, EHOMO), global hardness (η) and electrophilicity (ω) are used to explain the reactivity of the conformers. Aromaticity of the conformers is gauged in terms of nucleus independent chemical shift (NICS). The out of plane component, (NICS)zz values advocate that the conformers are less aromatic compared to benzene. 1,2-alternate and 1,3-alternate conformers showed absorption peaks at higher wavelengths compared to the cone and partial cone conformers.

Magnetization reversal dependence on magnetic properties of a spin torque oscillator with in-plane anisotropy free layer and orthogonal polarizer

The effect of magnetic properties on magnetization dynamics is studied for a spin torque oscillator (STO) composed of a free layer with an in-plane magnetic anisotropy and a reference layer with a fixed out-of plane magnetization. A transition from damped to uniform oscillations is observed for a critical value of saturation magnetization MS). In the uniform oscillations regime, the frequency is inversely proportional to MS. Similarly, the critical current for achieving uniform oscillations is investigated as a function of free layer intrinsic properties. In a second part of the study, the magnetostatic field (Hm) from the reference layer is considered and it is revealed that the out-of plane component of magnetization has a strong dependence on Hm. For a particular configuration, Hm could reduce the out-of plane component maximizing thus the out-put signal of the STO.

Integrated structure for a resonant micro-gyroscope and accelerometer

This paper presents the study of the mechanical behavior of a microstructure designed to detect acceleration and angular velocity simultaneously. The new resonant micro-sensor proposed, fabricated by the ThELMA© surface-micromachining technique, bases detection of two components of external acceleration (one in-plane component and one out-of plane component) and two components of angular velocity (roll and yaw) on the variation of frequency of several elements set in resonance. The device, despite its small dimensions, provides a differential decoupled detection of four external quantities thanks to the presence of four slender beams resonating in bending and four torsional resonators.

In-plane and out-of-plane spin precession in lateral spin-valves

The spin signal variations of Al/NiFe lateral spin-valves with AlOx interfaces are studied under different applied field orientations. For applied fields perpendicular to the sample plane, the spin signal is governed by the spin precession and by the angular dephasing of spins in the channel, i.e., the Hanle effect. We show that using narrow permalloy wires with large shape anisotropies, it is also possible to observe spin precession with in-plane magnetic fields. In this case, the precessing spin current possesses an out-of plane component, which means that by tuning properly the external field it is possible to control along the three dimensions the orientation of the spins arriving on the ferromagnetic detector. Finally, fits of our data allow for both in and out-of plane fields extracting the relevant characteristics of our lateral spin-valves.

Mechanism of reversing the Neel domain walls in the Co nanostripes with transverse magnetic anisotropy

We present a model of reversing the Neel domain walls (DWs) in the laminar domain structure of epitaxial Co(111) nanostripes. The laminar domain structure in nanostripes is induced by magnetic anisotropy, the easy axis of which is orthogonal to the long axis and lies in the plane of the stripes. Magnetization reversal in the DWs occurs by nucleation of vortices at the opposite ends of adjacent DWs and their subsequent propagation along the domain DWs. Vortices in adjacent DWs have opposite chirality. The out of plane component of the magnetization in the vortices cores is confirmed by micromagnetic modeling.

Residual stresses and clamped thermal expansion in LiNbO3 and LiTaO3 thin films

Residual stresses in LiNbO3 and LiTaO3 epitaxial thin films were evaluated taking into account Li nonstoichiometry by means of Raman spectroscopy and x-ray diffraction. The epitaxial films were grown on C-cut sapphire substrates by pulsed injection metal organic chemical vapour deposition. Clamping of the epitaxial films by the substrate induced a transfer from the in plane thermal expansion to the out of plane component. The temperature of the phase transition of clamped LiTaO3 films was close to that expected for a bulk sample.

Fundamental Research on Development of Liquid Crystalline Micro-Actuator

As a purpose of developing new micro-actuator driven by the liquid crystal flow, transient behaviors of a nematic liquid crystal between two parallel plates are computed with parameter of twist angle. The Frank and Leslie-Ericksen theory were used. When the twist angle is 0 deg, the induced flow is planar, and when the twist angle is not 0 deg, the flow has a out of plane component. The twist angle has little effect to the time characteristics of the flow. In the experiment, the applied voltage of 5 was used, and the results are in agreement with the calculation results.

Numerical Study on Liquid Crystalline Actuators Using Back-Flow Effect

As a purpose of developing micro-actuators driven by liquid crystals, transient behaviors of a nematic liquid crystal between two parallel plates under an electric field have investigated numerically by using the Leslie-Ericksen theory. Twist angle has been selected as computational parameters. Imposition of an electric field on a liquid crystal induces backflow whose profile and magnitude depend strongly on the twist angle of the director. When the twist angle is 0 degree, the induced flow is planar, and with increasing of the twist angle, the flow has an out of plane component, and finally the profile becomes unidirectional when the twist angle reaches 180 degrees.