Direction Of External Magnetic Field Research Articles

Mode conversion and laser energy absorption by plasma under an inhomogeneous external magnetic field.

The interaction of a high-frequency laser with plasma in the presence of an inhomogeneous external magnetic field has been studied here with the help of particle-in-cell simulations. It has been shown that the laser enters the plasma as an extraordinary wave (X-wave), where the electric field of the wave oscillates perpendicular to both the external magnetic field and propagation direction and as it travels through the plasma, its dispersion property changes due to the inhomogeneity of the externally applied magnetic field. Our study shows that the X-wave's electromagnetic energy is converted to an electrostatic mode as it encounters the upper-hybrid (UH) resonance layer. In the later stage of the evolution, this electrostatic wave breaks and converts its energy to electron kinetic energy. Our study reveals two additional processes involved in decay of the electrostatic mode at the UH resonance layer. We have shown that the energy of the electrostatic mode at the upper-hybrid resonance layer also converts to a low-frequency lower-hybrid mode and high-frequency electromagnetic harmonic radiations. The dependence of energy conversion processes on the gradient of the external magnetic field has also been studied and analyzed.

Fiber Vector Magnetometer Based on Polarization-Maintaining Fiber Long-Period Grating With Ferrofluid Nanoparticles

An opticalfiber vector magnetometer based on a thin-cladding polarization-maintaining fiber (TPMF) long-period fiber grating (LPFG) and magnetic fluid (MF) is proposed and experimentally demonstrated. The non-circular symmetric fiber structure and asymmetric evanescence field distribution of the LPFG induce a vector surrounding refractive index (SRI) response. Based on the magneto-optical properties of the MF nanoparticles and the directional SRI characteristics of the TPMF-LPFG, the resonance dip wavelength shift of the grating is dependent on the angle between the principal axis of TPMF and the external magnetic field direction when being applied to an external magnetic field. The achieved maximum sensitivity of the wavelength shift was −618 pm/mT when the magnetic intensity changes in the range of 0–10.5 mT. The achieved maximum orientation sensitivity of the sensor was 72 pm/degree, but the magnetic orientation can be detected only within the range of 0–90 degree. The minimum magnetic field intensity that can be detected is about 32.3 μT due to the 0.02 nm wavelength resolution of the optical spectrum analyzer. Our study proves that the high birefringence fiber based LPFG combined with MF can be developed as a high-performance vector magnetometer and such type of sensor is anticipated to find potential applications in magnetic or electric field systems.

Tunable nonreciprocal transmission based on non-Hermitian optical system with magnetic optical materials in a one-dimensional multilayer structure

In this study, a one-dimensional composite structure composed of a PT-symmetric system and magnetic optical (MO) materials is designed. The nonreciprocal propagation of a one-dimensional multilayer structure is investigated both theoretically and numerically based on the transfer matrix theory. Different from the single nonreciprocal frequency in the parity-time (PT) system, two adjacent band gaps are changed into a pair of nonreciprocal bands under the effect of MO materials and a PT system above the PT exceptional point, and extraordinary transmissions are inspired in some nonreciprocal frequencies. At the same time, the nonreciprocal propagation bands can be tuned based on the different choices of external magnetic field directions. Furthermore, with an increase in the gain/loss factor, the two nonreciprocal band gaps both disappear and form two bands with an extraordinary transmission at certain frequencies. Such peculiar properties in the composite structure may have broad potential applications in communication and integration devices.

Cross-waveguide based on sunflower-type eightfold quasiperiodic magnetic photonic crystal

Nonreciprocal waveguides play a key role in optical communication devices due to their robustness in unidirectional transmission along the edge. We proposed a unidirectional air guide waveguide structure based on eightfold sunflower quasiperiodic magnetic photonic crystal (PC) that has a large working bandwidth, high transmission efficiency, and strong stability. A cross-waveguide is constructed in the sunflower-type eightfold quasiperiodic magnetic PC structure. It can be used as a single-pole double-throw switch by changing the external bias magnetic field direction, in which the isolation is over 28 dB in the microwave band from 4.21 to 4.5 GHz and insertion loss is close to 0.001 dB. It can also achieve 1 × 2 or 1 × 3 equal ratio beam splitting, with a total transmission rate of close to 100% and transmission loss of 0.001 dB. The cross-waveguide is simple in structure and easy to integrate and manufacture, and it has a wide range of functions that have tremendous potential applications in optical communication systems.

Anisotropic effect of dipolar interaction in ordered ensembles of nanoparticles

We implement extensive computer simulations to investigate the hysteresis characteristics in the ordered arrays (lx × ly) of magnetic nanoparticles as a function of aspect ratio Ar = ly/lx, dipolar interaction strength hd, and external magnetic field directions. We have considered the aligned anisotropy case, α is the orientational angle. It provides an elegant en route to unearth the explicit role of anisotropy and dipolar interaction on the hysteresis response in such a versatile system. The superparamagnetic character is dominant with weak dipolar interaction (hd ≤ 0.2), resulting in the minimal hysteresis loop area. Remarkably, the double-loop hysteresis emerges even with moderate interaction strength (hd ≈ 0.4), reminiscent of antiferromagnetic coupling. These features are strongly dependent on α and Ar. Interestingly, the hysteresis loop area increases with hd, provided Ar is enormous, and the external magnetic field is along the y-direction. The coercive field μoHc, remanent magnetization Mr, and the heat dissipation EH also depend strongly on these parameters. Irrespective of the external field direction and weak dipolar interaction (hd ≤ 0.4), there is an increase in μoHc with hd for a fixed α and Ar ≤ 4.0. The dipolar interaction also elevates Mr as long as Ar is huge and the field is along the y-direction. EH is minimal for negligible and weak dipolar interaction, irrespective of Ar, α, and the field directions. Notably, the magnetic interaction enhances EH if Ar is enormous and the magnetic field is along the long axis of the system. These results are beneficial in various applications of interest such as digital data storage and spintronics. (a) Schematic of the two-dimensional array of nanoparticles. The variation of heat dissipation EH as a function of dipolar interaction strength and anisotropy axis orientation is shown in (b)-(d). The magnetic field is applied along the x-direction in (b). In contrast, the magnetic field is applied along y-direction in (c) and (d).

Generation and Control of Terahertz Spin Currents in Topology-Induced 2D Ferromagnetic Fe3 GeTe2 |Bi2 Te3 Heterostructures.

Future information technologies for low-dissipation quantum computation, high-speed storage, and on-chip communication applications require the development of atomically thin, ultracompact, and ultrafast spintronic devices in which information is encoded, stored, and processed using electron spin. Exploring low-dimensional magnetic materials, designing novel heterostructures, and generating and controlling ultrafast electron spin in 2D magnetism at room temperature, preferably in the unprecedented terahertz (THz) regime, is in high demand. Using THz emission spectroscopy driven by femtosecond laser pulses, optical THz spin-current bursts at room temperature in the 2D van der Waals ferromagnetic Fe3 GeTe2 (FGT) integrated with Bi2 Te3 as a topological insulator are successfully realized. The symmetry of the THz radiation is effectively controlled by the optical pumping incidence and external magnetic field directions, indicating that the THz generation mechanism is the inverse Edelstein effect contributed spin-to-charge conversion. Thickness-, temperature-, and structure-dependent nontrivial THz transients reveal that topology-enhanced interlayer exchange coupling increases the FGT Curie temperature to room temperature, which provides an effective approach for engineering THz spin-current pulses. These results contribute to the goal of all-optical generation, manipulation, and detection of ultrafast THz spin currents in room-temperature 2D magnetism, accelerating the development of atomically thin high-speed spintronic devices.

Magnetic anisotropy and reversal in epitaxial FeGa/IrMn bilayers with different orientations of exchange bias

Epitaxial FeGa/IrMn bilayers with exchange biases along the FeGa[100] and [110] directions are prepared on MgO(001) single crystal substrates by magnetron sputtering through controlling the orientation of the external field <i>in situ</i> applied during growth. The effect of the exchange bias orientation on the magnetic switching process and the magnetic switching field are studied. The X-ray <i>φ</i>-scan indicates that the FeGa layer is epitaxially grown with a 45° in-plane rotation on the MgO(001) substrate along the FeGa(001)[110] direction and the MgO(001)[100] direction. The measurements of the angular dependence of the ferromagnetic resonance field and the corresponding fitting to the Kittel equation show that the samples have a superposition of fourfold symmetric magnetocrystalline anisotropy <inline-formula><tex-math id="M4">\begin{document}$ {K}_{1} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M4.png"/></alternatives></inline-formula>, unidirectional magnetic exchange bias anisotropy <inline-formula><tex-math id="M5">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M5.png"/></alternatives></inline-formula>, and uniaxial magnetic anisotropy <inline-formula><tex-math id="M6">\begin{document}$ {K}_{\mathrm{u}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M6.png"/></alternatives></inline-formula> with configuration of <inline-formula><tex-math id="M7">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[100\right] $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M7.png"/></alternatives></inline-formula> or <inline-formula><tex-math id="M8">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[110\right] $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M8.png"/></alternatives></inline-formula>. The combined longitudinal and transverse magneto-optical Kerr effect measurements show that sample with <inline-formula><tex-math id="M9">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[100\right] $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M9.png"/></alternatives></inline-formula> exhibits square loops, asymmetrically shaped loops, and one-sided two-step loops in different external magnetic field directions. In contrast, the sample with <inline-formula><tex-math id="M10">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[110\right] $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M10.png"/></alternatives></inline-formula> exhibits one-sided two-step and two-sided two-step loops as the magnetic field orientation changes. Because the <inline-formula><tex-math id="M11">\begin{document}$ {K}_{1} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M11.png"/></alternatives></inline-formula> is superimposed by <inline-formula><tex-math id="M12">\begin{document}$ {K}_{\mathrm{u}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M12.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M13">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M13.png"/></alternatives></inline-formula>, the in-plane fourfold symmetry of the magnetic anisotropy energy is broken. The local minima are no longer strictly along the in-plane <inline-formula><tex-math id="M14">\begin{document}$ \left\langle{100}\right\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M14.png"/></alternatives></inline-formula> directions, but make a deviation angle which depends on the relative orientation and strength of magnetic anisotropy. A model based on the domain wall nucleation and propagation is proposed with considering the different orientations of <inline-formula><tex-math id="M15">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M15.png"/></alternatives></inline-formula>, which can nicely explain the change of the magnetic switching route with the magnetic field orientation and fit the angular dependence of the magnetic switching fields, indicating a significant change of domain wall nucleation energy as the orientation of <inline-formula><tex-math id="M16">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M16.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M16.png"/></alternatives></inline-formula> changes.

Low frequency Compressional modes in degenerate semiconductor plasmas

Properties of low frequency compressional electromagnetic wave pulse in a magnetized semiconductor hole-electron plasma, are investigated. The quantum mechanical effects such as Fermi pressure, quantum tunneling and exchange-correlation potential of inertialess electrons, inertial holes and stationary charged ion particulates are considered in the presence of the magnetic field. A new type of dispersion relation is derived for low-frequency compressional waves by employing quantum magneto-hydrodynamic model and Maxwell equations; the dispersion relation is then analyzed for parallel, perpendicular and oblique propagation of compressional electromagnetic wave pulse to the external magnetic field direction. We have analyzed the obtained dispersion relations numerically, for different semiconductor plasma such as GaAs, GaSb and, GaN, the graphs shows that the frequency of compressional electromagnetic wave pulse decreases with increase of electron-hole density concentration, whereas the frequency increases with the increase of angle of propagation compressional electromagnetic wave pulse. Our results are applicable to understanding the dynamics of semiconductor plasma to produce high power, high band-width devices in contrast to the existing gas plasma devices. Keywords: degenerate semiconductor plasma, quantum mechanical effects, compression electromagnetic wave, gas plasma device.

Incommensurate and commensurate antiferromagnetic states in CaMn2As2 and SrMn2As2 revealed by As75 NMR

We carried out $^{75}\mathrm{As}$ nuclear magnetic resonance (NMR) measurements on the trigonal $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ and $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ insulators exhibiting antiferromagnetic (AFM) ordered states below N\'eel temperatures ${T}_{\mathrm{N}}=62$ and 120 K, respectively. In the paramagnetic state above ${T}_{\mathrm{N}}$, typical quadrupolar-split $^{75}\mathrm{As}$ NMR spectra were observed for both systems. The $^{75}\mathrm{As}$ quadrupolar frequency ${\ensuremath{\nu}}_{\mathrm{Q}}$ for $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ decreases with decreasing temperature, while ${\ensuremath{\nu}}_{\mathrm{Q}}$ for $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ increases, showing an opposite temperature dependence. In the AFM state, the relatively sharp and distinct $^{75}\mathrm{As}$ NMR lines were observed in $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ and the NMR spectra were shifted to lower fields for both magnetic fields $H\ensuremath{\parallel}c$ axis and $H\ensuremath{\parallel}ab$ plane, suggesting that the internal fields ${B}_{\mathrm{int}}$ at the As site produced by the Mn ordered moments are nearly perpendicular to the external magnetic field direction. No obvious distribution of ${B}_{\mathrm{int}}$ was observed in $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$, which clearly indicates a commensurate AFM state. In sharp contrast to $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$, broad and complex NMR spectra were observed in $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ in the AFM state, which clearly shows a distribution of ${B}_{\mathrm{int}}$ at the As site, indicating an incommensurate state. From the analysis of the characteristic shape of the observed spectra, the AFM state of $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ was determined to be a two-dimensional incommensurate state where Mn ordered moments are aligned in the $ab$ plane. A possible origin for the different AFM states in the systems was discussed. Both $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ and $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ show very large anisotropy in the nuclear spin-lattice relaxation rate $1/{T}_{1}$ in the paramagnetic state. $1/{T}_{1}$ for $H\ensuremath{\parallel}ab$ is much larger than that for $H\ensuremath{\parallel}c$, indicating strong anisotropic AFM spin fluctuations in both compounds.

Interaction between surface acoustic waves and spin waves in a ferromagnetic thin film

We present a theoretical description of magnon–phonon interactions in a multilayer structure containing a ferromagnetic thin film. The formalism is applicable to an arbitrary direction of external magnetic field and various types of acoustic waves including Rayleigh and Love surface modes. A particular attention is paid to the spatial profile of the acoustic wave modes and analytical expressions for the effective coupling coefficients are derived taking into account the degree of mode profile overlap between spin waves and acoustic waves. The results are applied to reproduce a strongly anisotropic and non-reciprocal linewidth of acoustic ferromagnetic resonance reported in a recent experiment.

Ultra-deep optical cooling of coupled nuclear spin-spin and quadrupole reservoirs in a GaAs/(Al,Ga)As quantum well

The physics of interacting nuclear spins in solids is well interpreted within the nuclear spin temperature concept. A common approach to cooling the nuclear spin system is adiabatic demagnetization of the initial, optically created, nuclear spin polarization. Here, the selective cooling of 75As spins by optical pumping followed by adiabatic demagnetization in the rotating frame is realized in a nominally undoped GaAs/(Al,Ga)As quantum well. The lowest nuclear spin temperature achieved is 0.54 μK. The rotation of 6 kG strong Overhauser field at the 75As Larmor frequency of 5.5 MHz is evidenced by the dynamic Hanle effect. Despite the presence of the quadrupole induced nuclear spin splitting, it is shown that the rotating 75As magnetization is uniquely determined by the spin temperature of coupled spin-spin and quadrupole reservoirs. The dependence of heat capacity of these reservoirs on the external magnetic field direction with respect to crystal and structure axes is investigated.

Anisotropic magnetoresistance and memory effect in bulk systems with extended defects

To describe kinetic phenomena in disordered conductors, various acts of scattering of electrons can be often considered as independent, that is captured by the Boltzmann equation. However, in some regimes, especially, in a magnetic field, it becomes necessary to take into account the correlations between different scattering events of electrons on defects at different times in the past. Such memory effects can have a profound impact on the resistivity of 2D semiconductor systems, resulting in giant negative magnetoresistance and microwave-induced resistance oscillations phenomena. This work opens the discussion of the memory effects in 3D conducting systems featured by the presence of extended one-dimensional defects, such as screw dislocations or static charge stripes. We demonstrate that accounting for the memory effect, that is the capture of electrons on collisionless spiral trajectories winding around extended defects, leads to the strong negative magnetoresistance in case when the external magnetic field direction becomes parallel to the defects axis. This effect gives rise to a significant magnetoresistance anisotropy already for an isotropic Fermi surface and no spin–orbit effects. The proposed resistivity feature can be used to detect one-dimensional scattering defects in these systems.

Doping-controlled surface conduction in topological insulators with warping effects

Based on a self-consistent t-matrix approximation, we explore the influence of magnetic and nonmagnetic doping on the surface electronic states and conductivity of topological insulators. We show that warping parameter has a crucial impact on the density of states and dc conductivity of the doped surfaces. As the warping strength is increased, the surface density of states at high energies is suppressed and the resonant states induced by impurities in the vicinity of the Dirac point gradually disappear. It is found that nonmagnetic impurities break electron-hole symmetry at low warping strength, while the symmetry remains unchanged when the surface is magnetically doped. Our findings reveal that surface conductivity can be controlled by tuning the doping, the direction of external magnetic field and that of impurity magnetic moments. Also, the surface conductivity features in topological insulators with warped energy dispersions are not significantly affected by the presence of impurities compared to that of materials with circular energy contour.

Chiral-induced spin selectivity in the formation and recombination of radical pairs: cryptochrome magnetoreception and EPR detection

That the rates and yields of reactions of organic radicals can be spin dependent is well known in the context of the radical pair mechanism (RPM). Less well known, but still well established, is the chiral-induced spin selectivity (CISS) effect in which chiral molecules act as spin filters that preferentially transmit electrons with spins polarized parallel or antiparallel to their direction of motion. Starting from the assumption that CISS can arise in electron transfer reactions of radical pairs, we propose a simple way to include CISS in conventional models of radical pair spin dynamics. We show that CISS can (a) increase the sensitivity of radical pairs to the direction of a weak external magnetic field, (b) change the dependence of the magnetic field effect on the reaction rate constants, and (c) destroy the field-inversion symmetry characteristic of the RPM. We argue that CISS polarization effects could be observable by EPR (electron paramagnetic resonance) of oriented samples either as differences in continuous wave, time-resolved spectra recorded with the spectrometer field parallel or perpendicular to the CISS quantization axis or as signals in the in-phase channel of an out-of-phase ESEEM (electron spin echo envelope modulation) experiment. Finally we assess whether CISS might be relevant to the hypothesis that the magnetic compass of migratory songbirds relies on photochemically-formed radical pairs in cryptochrome flavoproteins. Although CISS effects offer the possibility of evolving a more sensitive or precise compass, the associated lack of field-inversion symmetry has not hitherto been observed in behavioural experiments. In addition, it may no longer be safe to assume that the observation of a polar magnetic compass response in an animal can be used as evidence against a radical pair sensory mechanism.

Phase-field simulation of magnetic double-hole nanoring and its application in random storage

ABSTRACT As an ideal high-density storage unit, magnetic nanorings have become a research hotspot in recent years. We can both study the evolution of microscopic state of magnetization and acquire macroscopic magnetic properties by micromagnetic simulation, which has thus been widely used. However, traditional micromagnetism cannot simulate complex stress state. Due to the introduction of microelasticity theory, the phase field method for magnetic materials can be used to calculate the coupling effect of stress and magnetic field. However, the computing model usually needs to satisfy periodic boundary condition. In this paper, the phase field simulation combined with the finite element method is employed. By using user defined element, the evolution of magnetic domain structures of the double-hole nanorings has been studied. In different diameter of the holes and external magnetic field direction, we have found seven kinds of magnetic domain evolution mechanism. Among them, the twin-vortex evolution mechanism with high stability and low demagnetization interference characteristics of advantages, has good application prospect in magnetic random-access memory (MRAM) unit.

Preparation of one-dimensional magnetic nanocomposites with palygorskites as temples after inorganic modification

The hydrochloric acid (HCl), sodium hydroxide (NaOH) and hydrogen peroxide (H2O2) were used as inorganic modifiers for the surface modification of palygorskite (Pal). The Fe3O4 was attached on modified-palygorskite surface uniformly via coprecipitation in order to prepare magnetically oriented Pal@Fe3O4 one-dimensional nanocomposites. The effect of modifier kinds and concentration for Fe3O4 grow on palygorskite surface was evaluated carefully in this study. It was found that the acid modification and H2O2 modification of palygorskite could really help Fe3O4 nanoparticles grow on the nanorods, but the alkali treatment (after acid modification) gave the opposite effect. Especially the Fe3O4 nanoparticles could attached to modified-palygorskite uniformly when the modifier was HCl and the concentration was 2.0 mol/L. The Pal@Fe3O4 nanocomposites were superparamagnetic at room temperature without any coercivity, which could rapidly respond and orient to an external magnetic field. The brightness variation of magnetically oriented Pal@Fe3O4 under polarizing optical microscope (POM) in the direction of external magnetic fields, which provided a novel approach for the application of palygorskite as one-dimensional nanomaterials and optical active materials. Finally, a possible mechanism of inorganic modification was suggested. An appropriate concentration of HCl could not only improve the surface properties of palygorskite but also make palygorskite surface occupied by more H+ cations, which cause more Fe3+/Fe2+ cations absorbed on modified-Pal surface, leading to the Fe3O4 nanoparticles grow uniformly on palygorskite surface.

Effect of strength and direction of external magnetic field on dynamics of vortices in a square lid-driven cavity flow

In this study, the effect of magnetic field strength and its direction are considered on square lid-driven cavity flow. The whole range of applicable magnetic field strength which is used in practice up to now (0 to 10 Tesla) is accomplished in this research. The governing equations, including non-linear conservative equations of continuity, momentum and magnetic field equations are solved numerically. Continuity and momentum equations are solved by the finite volume method using SIMPLE algorithm, where the finite difference method is used in the magnetic field equation solving. In this research the effect of magnetic field on the velocity distribution, streamlines and vortex flow show that the vortices of the cavity shrink (decreases) up to 0.01 T where the uniform and vertical magnetic field applied from the bottom surface of the square cavity. For the magnetic field of 0.01 T, vortices in the cavity flow disappear. Higher values of the magnetic field create larger vortices. It was also concluded that the magnetic field has a strong effect on vortex formation, its size and location; therefore it can be used to control the vortex dynamics in a contactless way.

Спектральные характеристики прецессии положения равновесия намагниченности в нормально намагниченной ферритовой пластине.

Спектральные характеристики прецессии положения равновесия намагниченности в нормально намагниченной ферритовой пластине.

Effect of Direction of External Magnetic Field on Minimum Propagation Current of a Composite Conductor for LHD Helical Coils

The conductor for helical coils of the Large Helical Device consists of a Rutherford-type NbTi/Cu cable, a pure aluminum stabilizer, and a copper sheath. The dimensions of the conductor and the stabilizer cross-sections are 18.0 mm × 12.5 mm and 12.4 mm × 5.2 mm, respectively. The measured cold-end recovery current in the magnetic field parallel to the shorter side (B//12.5) is clearly lower than that in the field parallel to the longer side (B//18.0) because of the difference in magnetoresistance by Hall currents. Since the minimum propagation current Imp is important to determine the upper limit of operation current, Imp has been measured for two types of one-turn coil samples, which were bent flatwise (B//18.0) and edgewise (B//12.5) with the inner radius of 0.14 m to extend the length in the uniform background field of the test facility. The measured Imp at B//12.5 is almost the same as that at B//18.0 in spite of the large difference in the steady-state resistance. Imp is considered to be determined by the heat balance before the current diffuses deeply into the stabilizer.

Study of the possibility of suppressing the influence of changes in an external magnetic field direction on the relative frequency fluctuations of two rubidium atomic clocks

Study of the possibility of suppressing the influence of changes in an external magnetic field direction on the relative frequency fluctuations of two rubidium atomic clocks