Search

Copyright of Journal of Capital Normal University (Natural Science Edition) is the property of Journal of Capital Normal University (Natural Science Edition) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dynamic susceptibility of thin truncated conical permalloy nanodisk with height 20 nm is simulated using micromagnetic simulations. Starting from a relaxed magnetic vortex state, the effect of tapering on the resonant modes is analyzed by changing the bottom radius (R = 50 nmto 100 nm) and top radius (r = 10 nmtoR − 10 nm) of the conical nanodisk. When an in-plane excitation field pulse is applied, the lowest resonant peak frequency increases with increase in r. This mode is originated due to vortex core translation and the variation of the resonant peak with r is well explained using Thiele's equation. Other resonant modes appear at higher excitation frequencies which are identified as azimuthal modes. When an out-of-plane excitation field is applied, all the spin wave modes appear to be axially symmetric. Appearance of new resonant modes and shifting of the resonant frequency is recorded by changing either of the parameter r or R for both the excitation field directions. The spatial distribution of FFT of magnetization at each resonant mode links the area of nanodisk that has maximum contribution to each mode and combining this with average center of magnetization perturbation, shifting of resonance frequency is explained successfully. The findings from this study prove that tunable resonant frequency can be achieved by tapering of truncated conical nanodisks. [ABSTRACT FROM AUTHOR]

In the present work, we will study the superconducting properties of a mesoscopic three-dimensional prism with square transversal section under an external magnetic field in both Zero-Field Cooling (ZFC) and Field-Cooling (FC) process. The studied sample is a three-band system (with three condensates ψ 1 , ψ 2 , ψ 3 ), in which we take a Josephson type inter-band coupling simulated via γ parameter. We analyze the magnetization, superconducting electronic density and free Gibbs energy considering both processes. As results, we found an interesting tunneling of vortex and anti-vortex between the bands, and vortex cluster configuration in the sample. This behaviour is due to the non-monotonic interaction between the bands. [ABSTRACT FROM AUTHOR]

Our study sample is a superconducting bi-dimensional octagon with different boundary conditions immersed in a magnetic external field H. The boundary conditions are simulated by considering different values of the de Gennes extrapolation length b on different surfaces of the sample. Our investigation was carried out by solving the time-dependent Ginzburg–Landau equations. We analyzed the superconducting electron density and the magnetization curves as functions of H and temperature T in field-cooling and in zero-field-cooling processes for different values of b and size of the sample. We found a strong dependence of the critical fields on b and size of the sample. [ABSTRACT FROM AUTHOR]

In the present work, we studied the magnetization, vorticity, Cooper pairs density, and the spatial distribution of the local magnetic field in a three-dimensional superconductor with a SQUID geometry (a square with a central hole connected to the outside vacuum through a very thin slit). Our investigation was carried out in both the Meissner-Ochsenfeld and the Abrikosov state solving the two-band Ginzburg-Landau equations considering a Josephson coupling between the bands. We found a non-monotonic vortex behavior and the respective generation of vortex clusters due to the Josephson coupling used between condensates. [ABSTRACT FROM AUTHOR]

Magnetic nanodots are of high interest for basic research due to their broad spectrum of possible magnetic states and magnetization reversal processes. Besides, they are of technological interest since they can be applied in magnetic data storage, especially if vortex states occur in closed dots or open rings. While producing such nanorings and nanodots from diverse magnetic materials by lithographic techniques is quite common nowadays, these production technologies are naturally prone to small deviations of the borders of these nanoparticles. Here we investigate the influence of well-defined angular-dependent roughness of the edges, created by building the nanoparticles from small cubes, on the resulting hysteresis loops and magnetization reversal processes in five different round nanodots with varying open areas, from a thin ring to a closed nanodot. By varying the orientation of the external magnetic field, the impact of the angle-dependent roughness can be estimated. Especially for the thinnest ring, significant dependence of the transverse magnetization component on the field orientation can be found. [ABSTRACT FROM AUTHOR]

The vortex states in electron-doped high-Tc superconductors are studied theoretically at the mean-field approach and based on the Bogoliubov-de Gennes equations. The local density of states is calculated, through which the in-gap bound states are revealed. They are robust at the sites around the vortex core. In the underdoped region where the antiferromagnetic order and the superconducting order coexist, the in-gap peaks are lying symmetric with respect to the Fermi energy, while the peak intensities at the negative energy are much stronger. A stripe-type modulation is revealed for the spin-resolved local density of states. As the doping density increases to the optimal or over-doped region, the long-range antiferromagnetic order disappears, and the two in-gap peaks merge to one single peak. The peak position is near the Fermi energy. Our results indicate that the vortex states may be used to detect the signature of the antiferromagnetic order in electron-doped high-Tc superconductors. [ABSTRACT FROM AUTHOR]

We studied the (magnetic field-temperature) phase diagram, the resistive state, and the vortex configurations of a rectangular superconducting loop, under an electrical transport current J, and an external applied magnetic field H. We show that the critical current density in the I − V characteristic curve Jc1, at which the first vortex–antivortex (V-Av) pair nucleates in the sample, as well as the number of jumps in the I − V curve (i.e., different resistive states), strongly depends on the temperature of the sample and the spatial variation of critical temperature in the sample. [ABSTRACT FROM AUTHOR]

We analyzed the role of the inclusion of anti-dots on the vortex state and some calorimetric properties of a mesoscopic superconducting square immersed in an external applied magnetic field. We calculated the magnetization, entropy, Gibbs free energy, density of Cooper pairs and specific heat for this system in a zero field cooling process, solving the time-dependent Ginzburg–Landau equations. We found that the critical temperature is non-dependent on the number of anti-dots and dependent slightly on the size of the defects. Oscillations in the entropy and specific heat are found due the temperature dependence of the superconducting characteristics length. [ABSTRACT FROM AUTHOR]

Ordered ferromagnetic nanowire arrays are widely studied due to the diversity of possible applications. However, there is still no complete understanding of the relation between the array's parameters and its magnetic behavior. The effect of vortex states on the magnetization reversal of large-diameter nanowires is of particular interest. Here, we compare analytical and micromagnetic models with experimental results for three arrays of iron nanowires with diameters of 33, 52 and 70 nm in order to find the balance between the number of approximations and resources used for the calculations. The influence of the vortex states and the effect of interwire interactions on the remagnetization curves are discussed. It has been found that 7 nanowires treated by a mean field model are able to reproduce well the reversal behavior of the whole array in the case of large diameter nanowires. Vortex states tend to decrease the influence of the structural inhomogeneities on reversal process and thus lead to the increased predictability of the system. [ABSTRACT FROM AUTHOR]

We studied the influences of the inclusion of different geometrical defects (circle, triangle, and square) with different Ginzburg–Landau parameters κ on the vortex state of a mesoscopic superconducting square immersed in an external applied magnetic field. We calculated the magnetization, vorticity, and density of Cooper pairs for this system, solving the time-dependent Ginzburg–Landau equations. We found a novel and interesting behavior of the vorticity (N < 0) at low magnetic fields: a spontaneous generation of anti-vortices due to the breaking inversion symmetry. [ABSTRACT FROM AUTHOR]

Magnetic enhancement of Chinese loess‐paleosol sequences has been used extensively as a proxy for East Asian summer monsoon variations. However, the pedogenic magnetic particles contributing to this magnetic enhancement are difficult to extract, so it is not clear how they formed. In this study, we reveal pedogenic magnetite and hematite using electron microscopy, synchrotron radiation X‐ray diffraction, and rock magnetic methods. First‐order reversal curves indicate that superparamagnetic/single domain/vortex state magnetic properties dominated both loess and paleosol samples. Samples of muscovite and chlorite, which are paramagnetic, have weak spontaneous magnetization. The 1‐ to 10‐μm‐sized fraction of host silicatesis responsible for most of the magnetic enhancement of paleosols. In the paleosol fraction, we found weathered phyllosilicates (muscovite/chlorite), including many elongated submicron to a few microns authigenic magnetite and hematite particles between layers; however, few such interlayer particles were found in phyllosilicates of the loess fraction. The concentration of magnetite/hematite particles within paleosol muscovite/chlorite grains and in aggregates of phyllosilicate fragments is much higher than that of the submicron iron oxides found on silicate surfaces. Interlayer magnetite particles are dominantly prism‐shaped with aspect ratios >~4. The authigenic magnetite must be mainly responsible for the spontaneous magnetization of the muscovites and chlorites and the paleosol magnetic properties. The protective silicates account for the low extraction efficiency and also the near absence of surface oxidation of pedogenic magnetite. Based on our results, we suggest that magnetite/hematite in weathered phyllosilicates contribute significantly to the magnetic enhancement of mature paleosols. Key Points: Hundreds of nanometer‐micron‐sized authigenic magnetite/hematite particles are highly concentrated in paleosol muscovite/chlorite grainsThe authigenic iron oxides are mainly responsible for the weak spontaneous magnetization of weathered muscovite and chlorite grainsElongated authigenic magnetites account for the dominant single domain/vortex state magnetic property and magnetic enhancement in paleosols [ABSTRACT FROM AUTHOR]

Vortex patterns are determined for a three-dimensional mesoscopic superconductor with one central weak link, using the time-dependent Ginzburg-Landau equations. The vortex states are obtained for field orientation parallel and perpendicular to the weak link, and vortex rearrangements are found to occur in the vortex patterns. Tilting of the field leads to interesting phenomena caused by the small volume-to-surface ratio, as vortex tubes are preferentially oriented along the field direction while they are forced to be perpendicular to the surface. In addition, we can also observe the intersection of vortex tubes inside (or near) the weak link. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Nano- & Electronic Physics is the property of Sumy State University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Magnetic hysteresis of isotropic permalloy nanorings with outer diameter 200 nm and thickness 20 nm has been studied. The inner diameter is varied from 0 to 190 nm to accommodate wide range of samples from nanodisk to thin nanorings. Micromagnetic simulation of in-plane hysteresis curve of these nanorings reveals that the magnetic properties change gradually with the change of inner diameter. The hysteresis loss indicated by the area of the hysteresis loop, increases gradually with the increase in inner radius up to d = 174 nm. For inner diameter of 176 nm, the loop area decreases drastically and remains so for up to d = 180 nm. After that, a small increment of d results in a large increment of loop area. The remanent states are found to be vortex states for d = 0-180 nm and onion states for d > 180 nm. The changes are attributed to two parameters mainly: exchange energy and demagnetization energy. These two parameters depend on inner curvature of the ring, which is treated as a variable in this simulation work. The changes in loop area have been discussed in light of variation of these parameters. [ABSTRACT FROM AUTHOR]

The propagation characteristics of a slotline structure under the influence of a static magnetic field have been studied using the model developed by Mark W. Coffey and John R. Clem. The complex valued resistive boundary condition formulated using the Coffey and Clem (CC) model is used to modify the dyadic Green's function in the spectral domain for the slot transmission line. The propagation characteristics are then calculated using the Galerkin's procedure. The numerical results are presented for propagation parameters and quality factor for a wide range of applied field, reduced temperature and superconducting layer thickness. The increase of the magnetic field and temperature causes an increase in vortex motion which results in a corresponding change in the propagation parameters and quality factor. The variation in the quality factor with respect to the superconducting strip thickness is explained using vortex effects. [ABSTRACT FROM AUTHOR]

We have studied Josephson tunneling through a circularly polarized micron or submicron-size disk of a soft ferromagnetic material. Such a disk contains a vortex that exhibits rich classical dynamics and has recently been proposed as a tool to study quantum dynamics of the nanoscale vortex core. The change in the Josephson current that is related to a tiny displacement of the vortex core has been computed analytically and plotted numerically for disks used in experiments. It is shown that a Josephson junction with a magnetic disk in the vortex state can be an interesting physical system that may be used to measure the nanoscale motion of the magnetic vortex. [ABSTRACT FROM AUTHOR]

In this paper, ferromagnetic Co50Fe50 nanorings were fabricated by template-assisted sputtering deposition. The obtained Co50Fe50 nanorings have a good dimensional uniformity, with outer diameter of 360 nm, width of 50 nm and thickness of 40 nm. The magnetic properties of Co50Fe50 nanorings were investigated by micromagnetic simulations and vibrating sample magnetometer. We observed two parallel magnetic switching processes in the micromagnetic simulations of nanorings, the vortex formation process and onion rotation process, respectively. Quantitative analysis on the basis of experimental results indicates that 43.7% of the Co50Fe50 nanorings undergo the vortex formation process and others undergo the onion rotation process. [ABSTRACT FROM AUTHOR]

The quantized vortex state appearing in the recently discovered new states in hcp He since their discovery (Kim and Chan, Nature, 427:225-227, ; Science, 305:1941, ) is discussed. Special attention is given to evidence for the vortex state as the vortex fluid (VF) state (Anderson, Nat. Phys., 3:160-162, ; Phys. Rev. Lett., 100:215301, ; Penzev et al., Phys. Rev. Lett., 101:065301, ; Nemirovskii et al., , ) and its transition into the supersolid (SS) state (Shimizu et al., , ; Kubota et al., J. Low Temp. Phys., 158:572-577, ; J. Low Temp. Phys., 162:483-491, ). Its features are described. The historical explanations (Reatto and Chester, Phys. Rev., 155(1):88-100, ; Chester, Phys. Rev. A, 2(1):256-258, ; Andreev and Lifshitz, JETP Lett., 29:1107-1113, ; Leggett, Phys. Rev. Lett., 25(22), 1543-1546, ; Matsuda and Tsuneto, Prog. Theor. Phys., 46:411-436, ) for the SS state in quantum solids such as solid He were based on the idea of Bose Einstein Condensation (BEC) of the imperfections such as vacancies, interstitials and other possible excitations in the quantum solids which are expected because of the large zero-point motions. The SS state was proposed as a new state of matter in which real space ordering of the lattice structure of the solid coexists with the momentum space ordering of superfluidity. A new type of superconductors, since the discovery of the cuprate high T superconductors, HTSCs (Bednorz and Mueller, Z. Phys., 64:189, ), has been shown to share a feature with the vortex state, involving the VF and vortex solid states. The high Ts of these materials are being discussed in connection to the large fluctuations associated with some other phase transitions like the antiferromagnetic transition in addition to that of the low dimensionality. The supersolidity in the hcp solid He, in contrast to the new superconductors which have multiple degrees of freedom of the Cooper pairs with spin as well as angular momentum freedom, has a unique feature of possessing possibly only the momentum fluctuations and vortex ring excitations associated with the possible low dimensional fluctuations of the subsystem(s). The high onset temperature of the VF state can be understood by considering thermally excited low D quantized vortices and it may be necessary to seek low dimensional sub-systems in hcp He which are hosts for vortices. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the Institute of Science & Technology of Dumlupinar University / Dumlupinar Üniversitesi Fen Bilimleri Enstitüsü Dergisi is the property of Dumlupinar University, Institute of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research is to consider one of the promising project in Iraq because it contains a technology transfer; secondly this field of science is new technology in producing high-temperature superconductor wire. The purpose of our project is try to manufacture a prototype design of high-temperature superconductor wire type Bi-2223 system depending on the carbonate roots and nitrate roots. We got two samples of bulk superconductor BiSrCaCuO (2223-phase) from carbonate and nitrate roots and exhibited a critical temperature ( T=122, 118 K) respectively. The second part of the project is the wire production by shielding and the drawing of the wire due to our specification. The ( I- V) characteristic of produced wire was done to emphasize the presence of HTSc for the wire prepared from carbonate and nitrate roots within the liquid nitrogen temperature. The thing that was investigated in the I- V characteristic of the produced wire is the nonlinear behavior between the current and voltage at ( T=80 K). It was clear that the critical current value is equal to ( I=0.55 A). The superconductor wire prepared from nitrate roots showed a critical current ( I) of about ( I=0.51 A). [ABSTRACT FROM AUTHOR]

The dissipative mechanism at low current density is compared in three different classes of superconductors. This is achieved by measuring the resistance as a function of temperature and magnetic field in clean polycrystalline samples of NbSe2, MgB2 and Bi2Sr2Ca2Cu3O10 (BSCCO) superconductors. Thermally activated flux flow behaviour is seen in all the three systems and clearly identified in bulk MgB2. While the activation energy at low fields for MgB2 is comparable to Bi2Sr2Ca2Cu3O10, its field dependence follows a parabolic behaviour unlike a power-law dependence seen in Bi2Sr2Ca2Cu3O10. We analyse our results based on Kramer's scaling for grain boundary pinning in MgB2 and NbSe2. [ABSTRACT FROM AUTHOR]

Motivated by the controversy concerning the pairing symmetry of the superconducting sodium-doped cobalt oxide, we investigate the microscopic electronic structure of an f-wave superconductor in the vortex state by diagonalizing an effective Hamiltonian specified in the triangular lattice self-consistently. We find that the low-lying vortex core states are in essence extended for the nodal f-wave superconductors. In comparison, we find localized bound states in the vortex core of the fully-gapped (d + id')-wave superconductors. [ABSTRACT FROM AUTHOR]

We report measurements of the magnetic field induced microwave complex resistivity in REBa2Cu3O7−δ thin films, with RE = Y, Sm. Measurements are performed at 48 GHz by means of a resonant cavity in the end-wall-replacement configuration. The magnetic field dependence is investigated by applying a moderate (0.8 T) magnetic field along the c-axis. The measured vortex-state complex resistivity in YBa2Cu3O7−δ and SmBa2Cu3 7−δ is analyzed within the well-known models for vortex dynamics. It is shown that attributing the observed response to vortex motion alone leads to inconsistencies in the as-determined vortex parameters (such as the vortex viscosity and the pinning constant). By contrast, attributing the entire response to field-induced pair breaking leads to a nearly quantitative description of the data. [ABSTRACT FROM AUTHOR]

We show that the Wiedemann–Franz law is violated at zero temperature in the vortex state of a d-wave BCS superconductor with isotropic impurity scattering. We use a semiclassical approach to include the Doppler shift experienced by the quasiparticles due to the circulating supercurrents and consider as well the Andreev scattering from an array of vortices assumed to be randomly distributed. We also show that the vertex corrections to the electric conductivity, which can be large when there is significant anisotropy in the impurity scattering, become unimportant as the magnetic field is increased. For the thermal conductivity, the corrections remain negligible as in the absence of a magnetic field. [ABSTRACT FROM AUTHOR]

This talk briefly reviews the current experimental and theoretical developments in high Tc superconductivity, focusing on the pseudogap regime of the underdoped region of the phase diagram.We argue that the appearance of superconductivity cannot be explained based on the traditional approach of quasiparticles exchanging some bosons, and that something fundamentally different is called for. [ABSTRACT FROM AUTHOR]

Maximum-Entropy (ME) analysis is applied to muon-spin-rotation (μSR) data of RBa[sub 2]Cu[sub 3]O[sub y] (RBCO; R = Ho, Eu) vortex states. Our focus is on the prospect of antiferromagnetism (AF) associated with the vortex core. The ME transforms are fitted by two μSR signals: the vortex signal and the grain-boundary (GB) signal. Below T[sub c], the GB signals are well fitted by Gaussians for both EuBCO (T[sub c] = 94 K) and underdoped HoBCO (T[sub c] = 66 K). Below 0.5T[sub c], EuBCO and HoBCO vortex signals are best fitted using Lorentzians, instead of expected Gaussians. An estimate for an effective Neél temperature of an AF vortex core is about 30 K. Our AF-core search results for RBCO vortex states are discussed considering a magnetic origin of cuprate superconductivity. [ABSTRACT FROM AUTHOR]

We review our recent works on the vortex state in p-wave superconductors. First, in a magnetic field parallel to the c-axis, the square vortex lattice is most stable, except in the immediate vicinity of T = T c0. Second, the effect of impurities on H c2 is studied, which exhibits characteristics of unconventional superconductors. Finally, the a– b anisotropy in the upper critical field in a magnetic field is considered. This anisotropy provides important information about the fourfold term arising from the Fermi surface effect. [ABSTRACT FROM AUTHOR]

The vortex structure and its field dependence are studied in the clean limit on the basis of the quasi-classical Eilenberger theory to find their difference between $$d_{x^2 - y^2 }$$ - and s-wave pairings. We show the $$d_{x^2 - y^2 }$$ -wave nature and the vortex lattice effect on the local density of states around the vortex, and on the field dependence of the spatially averaged density of states. The $$d_{x^2 - y^2 }$$ -wave pairing introduces a fourfold symmetric structure around each vortex core in the pair potential and the internal field. With increasing field, their contribution becomes significant to the whole structure of the vortex lattice state. [ABSTRACT FROM AUTHOR]

In quasi-low-dimensional type II superconductors, the orbital pair-breaking effect is considerably reduced when the magnetic field is exactly aligned in a direction parallel to the highly conducting layer. Then, since the superconducting phase survives up to a very high magnetic field comparable to the Pauli-paramagnetic limit, we could expect some drastic phenomena, such as the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state. In this paper, we discuss the condition of the tilt angle for the appearance of the FFLO state, and also discuss the stable spatial structure of the FFLO state. Further, we show an example of a quasi-two-dimensional system in which the FFLO state is remarkably enhanced, that is, a two-dimensional tight binding system of appropriate hole concentrations. [ABSTRACT FROM AUTHOR]

Phase diagram of vortex states of high-T[sub c] superconductors with sparse columnar defects is obtained by Monte Carlo simulations. The Bragg–Bose glass phase characterized by hexagonal Bragg peaks and the diverging tilt modulus is observed at low doses for the first time. As the density of defects increases, the melting temperature increases. When the density of defects further increases, the transition to the Bose glass phase occurs. The interstitial liquid is observed between these glass phases and the vortex liquid phase. [ABSTRACT FROM AUTHOR]