Complicated Magnetic Structure Research Articles

Analysis of Nonlinear Characteristics for a Three-Phase, Five-Limb Transformer Under DC Bias

Monopole HVDC systems create dc current flow in the earth, which can cause the grounding location potential to rise relative to infinite spot and alters the working point of the transformer core. Because of the nonlinearity of the transformer core, the exciting current produces the amount of harmonics under dc bias. Past research has focused almost on simulation and testing dc bias problems of single-phase transformers. However, due to the complicated magnetic circuit structure in a three-phase five-limb transformer, there are some difficulties in studying its dc bias problem. In this paper, a new model and algorithm are proposed to find the nonlinear characteristics for the three-phase five-limb transformer under dc bias. Maxwell's equations are used to replace the magnetic circuit model of the transformer. By combining an electrical circuit with the nonlinear characteristic curve of the core, dc bias problems for a three-phase five-limb transformer are studied. Results show that the waveform of the no-load current and magnetic field intensity of the transformer are distorted under dc current inrush, and low-order harmonics increase with increasing dc current. Finally the interior and exterior nonlinear curve characteristics under dc bias are discussed.

Helical magnetic structure in a quasi-one-dimensional LiCu2O2 multiferroic crystal according to 63,65Cu NMR studies

The NMR spectra of 63Cu and 65Cu natural copper isotopes in a LiCu2O2 multiferroic single crystal compound have been measured above and below the temperature of magnetic phase transition (T c = 23 K) in zero magnetic field and in applied magnetic field H 0 = 94 kOe parallel to the c axis of the crystal. In LiCu2O2 below T c, a complicated helical magnetic structure with the magnetic moment of copper ions Cu2+ varying along the chain according to the harmonic law with the wave vector being incommensurate to the crystal lattice constants has been revealed. The experimental results have been successfully interpreted using the model based on the planar helical magnetic structure. It has been found that the plane of rotation for Cu2+ magnetic moments in LiCu2O2 does not coincide at H 0 = 0 with the ab plane. The high magnetic field (H 0 = 94 kOe) applied along the c axis of the single crystal does not affect the spatial orientation of the plane of rotation.

Multichannel Langmuir probe for turbulence study in Heliotron J

New multichannel Langmuir probe system was developed and installed to Heliotron J. The objective of the new probe is to characterize basic turbulence property and the resulting transport in advanced helical configuration. The probe developed here consists of four sets of triple probe and one pin for floating potential measurement. Initial experiments in neutral beam heating plasma were conducted and fluctuation profile of radial and poloidal electric fields and Reynolds stress were estimated. For precise evaluation of the electric fields and Reynolds stress, a technique to compensate radial change of tilt angle between probe array and magnetic surface was proposed and applied to the initial results obtained in edge region of Heliotron J where the complicated magnetic structure exists.

3D numerical MHD modeling of sunspots with radiation transport

AbstractSunspot fine structure has been modeled in the past by a combination of idealized magneto-convection simulations and simplified models that prescribe the magnetic field and flow structure to a large degree. Advancement in numerical methods and computing power has enabled recently 3D radiative MHD simulations of entire sunspots with sufficient resolution to address details of umbral dots and penumbral filaments. After a brief review of recent developments we focus on the magneto-convective processes responsible for the complicated magnetic structure of the penumbra and the mechanisms leading to the driving of strong horizontal outflows in the penumbra (Evershed effect). The bulk of energy and mass is transported on scales smaller than the radial extent of the penumbra. Strong horizontal outflows in the sunspot penumbra result from a redistribution of kinetic energy preferring flows along the filaments. This redistribution is facilitated primarily through the Lorentz force, while horizontal pressure gradients play only a minor role. The Evershed flow is strongly magnetized: While we see a strong reduction of the vertical field, the horizontal field component is enhanced within filaments.

Influence of multiple magnetic phases on the extrinsic damping of FeCo–SiO2 soft magnetic films

In order to investigate the high-frequency damping properties of the ferromagnetic film for the electromagnetic shielding applications, a series of (FeCo)2x/(Fe)x/(SiO2)1−3x nanogranular films with various volume fractions (x) were fabricated by alternate triple-target magnetron sputtering. The (FeCo)0.50/Fe0.25/(SiO2)0.25 film shows excellent soft magnetic properties (4πMs∼1.48T,Hce∼4.3Oe,ρ∼4.3μΩ m). In both ferromagnetic resonance (FMR) and frequency-dependent permeability spectra measurements, two resonance peaks of the permeability for this film are obtained, which can be attributed to the complicated magnetic structure of FeCo and Fe phases in the film. This multiphase system makes an additional contribution to the extrinsic damping. As a result, the higher natural resonance frequency f for the film is up to 2.75 GHz with full width at half maximum of about 2.5 GHz for the imaginary part μ∥; meanwhile, the real part μ/ is as high as 650 while f<1.3 GHz. These films could be novel candidates for the electromagnetic shielding applications.

Properties of Intermittent Bursts in Edge Plasma of LHD

In edge plasma in the Large Helical Device (LHD), incoherent fluctuations with intermittent density bursts were observed with a two-dimensional lithium beam probe that can measure electron density and its fluctuation two-dimensionally. Statistical analysis using a probability denstiy function (PDF) showed that those bursts have the characteristics of blobs, which have been observed in tokamaks. Two-dimensional PDF analysis indicates that the blobs originate in the ergodic layer outside the last closed flux surface and move to the outer region. Wavelet analysis showed that the direction of blob propagation is not always outward but is sometimes in arbitrary directions. These characteristics may be a result of the complicated magnetic field structure of the heliotron configuration.

Magnetism in PrPdSn and NdPdSn studied on single crystals

Abstract We present the results of specific heat, magnetization and susceptibility measurements performed on single crystals of PrPdSn and NdPdSn intermetallic compounds. Both compounds crystallize in the orthorhombic TiNiSi-type crystal structure and order antiferromagnetically at TN = 4.2(1) K (PrPdSn) and TN = 3.5(1) K (NdPdSn). NdPdSn also undergoes an order-to-order phase transition at T1 = 1.95(3) K. Both compounds exhibit high magnetocrystalline anisotropy at low temperatures and a complicated magnetic structure, which is underlined by the metamagnetic phase transitions of both compounds.

119Sn Mössbauer spectroscopy of the intermetallic compound HoRhSn

The powder X-ray diffraction data revealed that the structure of HoRhSn is isotypic with the hexagonal ZrNiAl type (space group P 6 ¯ 2 m ). Bulk magnetic AC and DC measurements have shown that this compound is ferromagnetic with a Curie temperature of T C = 6.3(2) K. The thermal variation of the hyperfine parameters has been studied in detail by 119Sn Mössbauer spectroscopy. Especially, large distribution of magnetic hyperfine fields observed at the tin sites points to a rather complicated magnetic structure of probably non-collinear character but with the magnetic holmium moments arranged in directions close to the c-axis.

Magnetic Resonance and Nature of Magnetism in CeB<sub>6</sub>

We report results of the study of the recently discovered magnetic resonance in CeB6, which is characteristic to the phase II in the magnetic phase diagram of this strongly correlated heavy fermion metal. Experiments were carried out in a wide frequency range /2=44-360 GHz in magnetic field up to 30 T. It is found that the previously reported magnetic resonance exists at all frequencies studied and the g-factor for this resonance increases with frequency from g(/2=44 GHz)~1.55 to g(/2>250 GHz)~1.7. In addition to the aforementioned mode of magnetic oscillations an additional magnetic resonance with the g-factor 1.2-1.3 is detected for the frequencies exceeding 200 GHz. This effect may be a consequence of a complicated magnetic structure of the phase II, which is not foreseen in the standard models of the low temperature magnetic ordering in CeB6.

Complicated magnetic field structure of the star HD 45583

Preliminary data on the magnetic field structure of the unique magnetic star HD 45583 are obtained. The observational data are well described by a configuration of two magnetic dipoles located on opposite sides relative to the star’s center, with their axes directed roughly in a radial direction. The positive monopoles are closer to the surface and the negative, closer to the star’s center. For this reason, there appear to be two positive magnetic poles on the star’s surface but no negative poles. The need for further observations of this unique object is pointed out.

Visible Images Induced by the Three-Dimensionally Complicated Structure of the Plasma Periphery in the Large Helical Device

The magnetic components produced by nonaxisymmetric superconducting coils in the Large Helical Device produce a complicated magnetic structure in the plasma periphery, which strongly depend on the configuration of electric currents in the magnetic coils. A tangentially viewing charge-coupled device camera has observed line emission of doubly ionized carbon CIII. The dependence of the 3-D distribution of the CIII emission on magnetic configurations will be discussed.

Study of a Closed Divertor Configuration for the Three-Dimensionally Complicated Magnetic Structure in the LHD Plasma Periphery

The distribution of strike points in a closed divertor configuration with additional baffle plates installed in the toroidal ends of closed divertor components near lower/upper ports is calculated by tracing magnetic field lines from the last closed flux surface in various magnetic configurations (radial position of the magnetic axis, Rax = 3.50 ∼ 3.90 m). The calculation shows that the ratio of the number of strike points on additional plates is maximum for Rax = 3.60 m, showing that the plates are effective in this magnetic configuration. Neutral particle transport is investigated using a fully three-dimensional code EIRENE with one-dimensional plasma fluid analysis of divertor legs, where the plasma parameter profiles on the legs are obtained by an iterative calculation including interaction processes between the plasma and neutral particles. The plates raise the pressure of molecular hydrogen locally near the baffle plates to more than 0.2 Pa, which is enough for efficient particle control using vacuum pumping systems installed near the plates. The simulation proposes one possible candidate of optimized closed divertor configuration for the three-dimensionally complicated magnetic structure in the LHD plasma periphery.

31P-NMR and [formula omitted] studies of filled skutterudite compounds RRu 4P 12 (R: Sm, Gd)

The 31P nuclear magnetic resonance ( 31P-NMR) and muon spin relaxation ( μ SR ) of the filled skutterudite compounds SmRu 4P 12 and GdRu 4P 12 have been carried out. The 31P-NMR spectra of SmRu 4P 12 indicate a complicated magnetic structure in high magnetic fields. A successive anomaly of the spin-lattice relaxation rate in SmRu 4P 12 was also observed in high fields. The μ SR of both SmRu 4P 12 and GdRu 4P 12 shows the appearances of static internal magnetic fields below the metal–insulator transition temperature of 16.5 K and below the antiferromagnetic transition temperature of 22 K, respectively.

Magnetic and electronic properties of the antiferromagnetic YbFe4Al8 compound

The magnetic, electrical and electronic properties of the tetragonal ternary YbFe4Al8 compound have been investigated. This compound was supposed to be an antiferromagnetic superconductor due to the negative magnetization signal appearing at a low field of the field cooling mode, however, based on the measurements of the temperature dependence of magnetization and resistivity we do not confirm the presence of superconductivity in this material and we ascribe the negative magnetization to the complicated non-collinear magnetic structure. A switch to the antiferromagnetic order at about 150 K has been visible both on the M(T) and ρ(T) curves. The valence state of the Yb ions has been studied by X-ray photoemission spectroscopy. The valence band spectrum at the Fermi level exhibits the domination of the hybridized Yb(4f) and Fe(3d) states.

Magnetoconvection in an inclined magnetic field: linear and weakly non-linear models

Recent observations of sunspots have revealed a rich range of behaviour and a complicated magnetic field structure; magnetoconvection is the key physical process underlying these phenomena. Traditional studies of magnetoconvection have considered vertical, or sometimes horizontal, imposed fields. Tilted fields have received less attention, and yet these are crucial to sunspot dynamics, particularly in the penumbra where field lines are inclined at a variety of angles to the vertical. Tilting the field is also interesting from a purely theoretical viewpoint since it breaks many of the symmetries usually associated with convection problems. In this paper we study the linear stability of a layer permeated by an inclined magnetic field and go on to set up model equations in order to study the patterns formed in the weakly non-linear regime. Possible applications of the results to sunspots are discussed.

Studies of the magnetic ordering in the spinel system Zn 0.4Co 0.6Al xFe 2− xO 4 by neutron diffraction

Magnetic properties of the spinel ferrite Zn 0.4Co 0.6Al x Fe 2− x O 4 with x = 0.0, 0.25, 0.50, 0.75 and 1.0 have been investigated by neutron diffraction studies in the temperature range 800 K ≥ T ≥ 17 K. The distributions of the magnetic moments in the A and B sublattices and their ordering as a function of temperature and composition have been obtained. The B sublattice magnetization deviates from the usual Brillouin function. An increasing loss in B sublattice magnetization with increasing x causing gradual destabilization of the ferrimagnetic order has been revealed. A ferromagnetic transition is found to take place before reaching the paramagnetic state at higher x values. The net magnetization becomes zero at some temperatures for compositions x ≤ 0.75 indicating a state of spin compensation. The presence of a diffuse signal at low temperature causing significant broadening of the (1 1 1) Bragg peak indicates the formation of magnetic spin clusters in the system. The diffuse signal slightly fluctuates with temperature indicating freezing of the clusters at some temperatures. The progressive loss of B moment combined with the superposition of magnetic short-range clusters over the magnetic long-range order has induced a complicated magnetic structure in the system. The features observed in the neutron results suggest several transitions for the system: (i) a ferromagnetic transition for x ≥ 0.75 before the paramagnetic state is reached; (ii) a spin compensation state or anti-ferromagnetic state at some temperatures when the A and B sublattice moments become equal in magnitude for x ≤ 0.75; (iii) a semi-spin glass like state for x ≥ 0.75 as evident from the very high reduction in ordered B sublattice moment and freezing effect of short-range clusters.

Properties of Remote Flare Ribbons Associated with Coronal Mass Ejections

To understand the large-scale structure of flares and coronal mass ejections, we studied the motion and properties of remote flare ribbons of three major events: 2003 May 27 X1.3, 2000 November 24 X1.8, and 2000 November 25 X1.9 flares. The remote ribbons are in addition to the typical two-ribbon pairs in the flare cores. We found two common properties of these three events. First, the flare core occurs at the edge of a major sunspot, associated with flux emergence parallel to the edge. Such a flux emergence formed complicated magnetic channel structure. Second, three flare ribbons are visible for each event. The first two make up a typical two-ribbon structure near the flare core. The third ribbon (remote ribbon) moves away from the flare site at a speed between 30 and 100 km s-1, several times larger than the nominal two-ribbon separation speed of flares. It is interesting to note that for the 2000 November 25 event, the remote ribbon first moved away in the same manner as the other two events; it then retracted after the flare emission peaked. We compared such an expansion/retraction motion with a limb event observed on 2001 April 15. We interpret the observed motion of remote ribbons by the interaction between the erupting flux rope in the flare core region and the overlying large-scale magnetic fields. For the 2000 November 25 event, the overlying field and flare core fields interacted twice, during the outward and inward motions.

Magnetization and neutron diffraction studies on FeCrP

Crystal structure and magnetic behaviour of FeCrP have been investigated using magnetization and neutron diffraction measurements. FeCrP crystallizes in orthorhombic FeZrP type structure (Pnma space group,Z = 4) in which Cr atoms occupy the pyramidal site and Fe atoms occupy the tetrahedral site with total preference. Structural parameters including positional parameters have been refined. The refined values of positional parameters for Fe and Cr are quite different from those in FeZrP. The nature of magnetization-temperature curve is suggestive of antiferromagnetic nature withTN = 280 (±10) K. Preliminary analysis of neutron diffraction pattern at 13 K is indicative of a rather complicated magnetic structure.

Optimization of asymmetric figure-8 undulator as circularly polarized light source

In the soft x-ray region, the demand for helicity switching of circularly polarized undulator radiation is increasing to study circular dichroism. The asymmetric figure-8 undulator is an insertion device to provide circularly polarized radiation (CPR) and a simple method of helicity switching which has been proposed and built at SPring-8. Because of its complicated magnetic structure, it is important to optimize the magnetic parameters for more effective utilization of CPR. Using an analytical method, the relation between the magnetic parameters to maximize the degree of circular polarization is obtained. The impact of the finite emittance of electron beams on the polarization performance is also investigated numerically.

Long Periodic Magnetic Structure in CeB2C2

In this paper, we provide information on the magnetic structure in tetragonal CeB2C2, which is isostructural with the antiferroquadrupolar (AFQ) ordering compound DyB2C2, and discuss peculiarities of CeB2C2 among the RB2C2 (R = rare earth) system. Some of the RB2C2 compounds, which have the tetragonal LaB2C2 type structure, 1) exhibit characteristic AFQ orderings with antiferromagnetic (AFM) orderings. For instance, DyB2C2 undergoes an AFQ ordering at TQ 1⁄4 24:7K, which is nearly ten times higher than those in other AFQ ordering compounds, and an AFM ordering at TN 1⁄4 15:3K with a complicated magnetic structure. Thus, the RB2C2 compounds are attracted our interests by characteristic AFQ and AFM orderings with tetragonal symmetry. Of this system, HoB2C2, TbB2C2 and ErB2C2 have long periodic magnetic ordering states with close periodicity in the c-plane. Moreover, in the long periodic states of HoB2C2 and TbB2C2, which show characteristic AFQ orderings, similar and anomalous magnetic diffuse scattering which can not be understood by only magnetic correlations was observed in the region surrounded by the satellite peaks by neutron diffraction. The close periodicity and the similar anomalous scattering in spite of the different 4f states implies that the long periodic states originate in some common mechanism in RB2C2; therefore, the long periodic states is worthy of clarifying in details to understand properties in RB2C2. Our preliminary neutron powder diffraction experiments suggest that CeB2C2 also has a long periodic magnetic ordering state; however, the periodicity and magnetic structure are not determined yet because of weakness of magnetic scattering intensity. To obtain more accurate information on the magnetic structure in CeB2C2, we performed neutron diffraction experiments on a single crystalline sample of CeB2C2. CeB2C2 undergoes a magnetic ordering at TN 1⁄4 7:3K with a sharp peak in the temperature dependence of specific heat CpðTÞ, and a successive transition at Tt 1⁄4 6:5K with a broad hump in CpðTÞ. The temperature dependence of magnetic susceptibility ðTÞ also shows an peak at TN when magnetic field is applied along the a and [110] directions without anisotropy in the c-plane, while no obvious anomaly was observed at Tt in ðTÞ. Since the c-plane is the magnetic easy plane, the magnetic moments lie in the c-plane. The single crystal for the neutron diffraction experiments was grown by the Czochralski method with a tri-arc furnace from the mixtures of 99.9% pure Ce, 99.5% pure B and 99.999% pure C. Natural B was enriched by B so that we avoided the strong absorption effect by B in natural B. The neutron diffraction experiments were performed on the Kinken (Institute for Materials Research) neutron diffractometer KSD installed at the reactor, JRR-3M, in Japan Atomic Energy Research Institute; the wave length was 1⁄4 1:52 A, and the collimation condition was 120-opensample-300. Figure 1 shows a Bragg peak found in this work at T 1⁄4 2:2K below Tt 1⁄4 6:5K. The magnetic origin is evident because the peak disappears above TN. From Gaussian fitting procedure, the centre of the peak was determined as (0.161(2), 0.161(2), 0.100(2)). The result indicates that the magnetic structure of CeB2C2 at 2.2K is a long periodic one with a propagation vector of k 1⁄4 ð ; ; 0Þ, where 1⁄4 0:161ð2Þ 1=6, 0 1⁄4 0:100ð2Þ 1=10. In fact, all the Bragg peaks observed at T 1⁄4 2:2K can be indexed with this propagation vector; therefore, the magnetic structure below Tt is represented with the single propagation vector, k 1⁄4 ð ; ; 0Þ. We can not discuss the correlation length of the magnetic ordering, because of the bad mosaicity of the sample. Figure 2 shows the temperature dependence of the integrated intensity of the peak in Fig. 1 with careful 150