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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]

Cylindrical nanodisks typically exhibit in-plane magnetization reversal comprising of nucleation and propagation of a vortex closure state. Present work investigates the magnetization reversal process in a cylindrical disk of radius ranging from 20 nm to 100 nm in which the flat surfaces at top and bottom are modified to convex shaped surfaces. It is found that the nucleation of vortex state no longer occurs as a result of this surface modification. Instead, a buckled magnetization state is nucleated which transforms to reverse buckled state yielding a square hysteresis loop. However, the out-of-plane hysteresis loop exhibits a vortex state at remanence. Analytical calculation of total free energy of both vortex as well as buckled state and the comparison thereof shows that the vortex state is ground state if radius of nanodisk is above 60 nm. Below this critical radius, buckled state is the ground state. But the non-appearance of vortex state at remanence in in-plane hysteresis loop of all of the nanodisks indicates a presence of energy barrier between vortex and buckled state. Height of the energy barrier is estimated using nudged elastic band method (NEBM) in all cases which proves that the energy barrier for vortex state weakens and the barrier for buckled state intensifies with the reduction of nanodisk size. At the critical radius of 60 nm , crossover of the two barrier heights occurs. Eventually, at the radius of 30 nm , the vortex state becomes totally unstable which can be toppled to buckled state with the slightest of perturbation. • In-plane hysteresis in convex nanodisk yields buckled state at remanence. • Remanent state is a vortex state for out-of-plane magnetization reversal. • Height of vortex to buckle state energy barrier decreases with radius. • Critical radius is 60 nm above which vortex is a stable state. [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]

Particles in vortex states have gained arising interests due to the additional degree of freedom—the orbital angular momentum (OAM) inherently existing in the state. With the increasing energy of vortex particles (photons, leptons etc), the research has gradually transitioned from the classical field regime to collisions of vortex particles in the quantum-field regime. The latter provides a new way to study the rich properties of particle physics. Here, we show the characteristics of vortex states in bremsstrahlung by deriving the corresponding scattering probability following the quantum-electrodynamics theory. The theory allows us to obtain the OAM distribution of the outgoing vortex photon and the law of OAM transfer during interaction. It is shown that the generated photon takes most of the initial electron OAM, especially when the latter is more energetic. The opening angle of outgoing particles in vortex bremsstrahlung is also significantly different from plane wave scattering. The effects of polarization and non-zero impact parameter are also discussed. The results illustrate the unique feature of vortex scattering and suggest a feasible way to generate high-energy vortex photons—a novel source in studying nuclear physics.

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]

• Temperature effect on minor loop parameters and magenetostatic interactions on Fe 70 Ga 30 thin film. • Increase in grain size leads to decrease in energy loss coefficient W F 0 and trough depth coefficient W R 0. • Evidence for the coexistence of multidomain and Vortex State (VS) in all the FeGa thin films from FORC. We report on the temperature evolution of pseudo magnetic properties and vortex state in Fe 71 Ga 29 thin films at different substrate temperatures (RT-25 °C, 50 °C, 75 °C, and 150 °C) using minor loop analysis and first-order reversal curves respectively. Phase purity of Fe 71 Ga 29 thin films confirmed with grazing incidence X–ray diffraction, which confirms the A2-type disordered phase. The minor loop parameters such as energy loss coefficient W F 0 (362 kOe.emu/cc to 278 kOe.emu/cc) and trough depth coefficient W R 0 (67.30 kOe.emu/cc to 50.23 kOe.emu/cc) values drop as grain size increases due to a reduction in defects as a result of an increase in substrate temperature. First-order reversal curves allow us to estimate the coercivity variation and switching field distribution that allow us to get information about magnetic interactions between the domains. Additionally, the contour plots of FORC and MFM phase images infer the coexistence of multidomain and Vortex State (VS) in all the Fe 71 Ga 29 thin films deposited at different substrate temperatures. [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.

Highlights • In iron nanodots with a broad range of thicknesses and diameters, 8 different magnetization reversal mechanisms were found. • Stability of single and double vortex states depends strongly on the nanodot thickness and diameter. • For relatively thick nanodots (min. 20 nm), the single-vortex state was always found to be the ground state. Abstract Magnetic nanodots are of high technological importance in diverse storage and spintronics applications, especially in bit patterned media. Magnetization reversal in such nanodots typically occurs either by coherent rotation of the magnetization or along a vortex state. Other mechanisms of magnetization reversal are scarcely described in the literature. Understanding and predicting the magnetization reversal processes, however, is of utmost importance due to the varying stray fields in the different states under evolution, influencing neighboring nanodots in an array or matrix-like structure. Besides, the stability of vortex states against magnetic field changes – which corresponds to typically broad field ranges with reversible modifications of the magnetic state – influences the robustness of magnetically stored information as well as the necessary external fields for writing new information. Here we report on micromagnetic simulations on nanodots with 10 different, representative diameters and 10 dot thicknesses, respectively, giving rise to 8 possible magnetization reversal processes and suggesting the preconditions for the nucleation and propagation of one or two vortices in cylindrical iron disks. We show the impact of the dimensions and aspect ratios on all phases of magnetization reversal. This study results in a phase diagram of the different magnetization reversal processes. [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]

The spin valve principle is the most prominent sensor design among giant- (GMR) and tunneling (TMR) magnetoresistive sensors. A new sensor concept with a disk shaped free layer enables the formation of a flux-closed vortex magnetization state if a certain relation of thickness to diameter is given. The low frequency noise of current-in-plane GMR sensing elements with different free layer thicknesses at different external field strengths has been measured. The measurements of the 1/f noise in external fields enabled a separation of magnetic and electric noise contributions. It has been shown that while the sensitivity is increasing with a decreasing element thickness, the pink noise contribution is increasing too. Still the detection limit at low frequencies is better in thinner free layer elements due to the higher sensitivity.

We investigated vortex states in small star-shaped Mo 80 Ge 20 plates both theoretically and experimentally. The numerical calculations of the Ginzburg–Landau equation have been carried out with the aid of the finite element method, which is convenient to treat an arbitrarily shaped superconductor. The experimental results were observed by using a scanning SQUID microscope. Through systematic measurements, we figured out how vortices form symmetric configuration with increasing the magnetic field. The vortex distribution tends to adapt to one of five mirror symmetric lines when vortices were located at the five triangular horns of a star-shaped plate. The crystalline homogeneity of a sample was confirmed by the X-ray diffraction and the superconducting properties so that vortices are easily able to move for accommodating vortices in the geometric symmetry of the star-shaped plate. The experimental vortex configurations obtained for a star-shaped plate are in good agreement with theoretical predictions from the nonlinear Ginzburg–Landau equation. [ABSTRACT FROM AUTHOR]

The spike state is a metastable vortex state, like phase slips and kinematic vortices, that arises and disappears at a single critical field, the one that sets the transition from the normal to the superconducting state. It has been theoretically predicted to exist in the mesoscopic scale (Cadorim et al., 2021 and de Oliveira et al., 2021) within a particular κ range, that defines the genuine type-I superconductor. The lifetime of the spike state is obtained here in case of a triangular cross section and found to be six times smaller than that of a circular cross section (de Oliveira et al., 2021). The extrusion process is distinct for these geometries, while in the latter case vortex bubbles are formed and exit the superconductor each one carrying a fraction of the trapped magnetic flux until its total depletion, in the former case the expulsion occurs at a single process. We use the time-dependent Ginzburg–Landau to describe the spike-state. [ABSTRACT FROM AUTHOR]

We have investigated hall effect on YBa2Cu3-xMxO7-δ (M=Ni, Fe) bulk samples, with dopant amount 0 ≤ x ≤ 0.045 for Ni and 0 ≤ x ≤ 0.03 for Fe, with magnetic field (H=2.52, 4.61, 6.27 kOe) perpendicular to sample’s surface with constant current 100 mA. Our study shows that as both dopants increases, TC decreases and it decreases faster by Ni . In these ranges of dopant and magnetic field the Hall sign reversal has been observed in all samples once and also ∆max has occurred in lower temperatures, its magnitude increases by Ni, and in Fe doped samples except in sample with dopant amount x=0.03, which almost decreases, that it can show effect of magnetic doping on hall effect.

• Evidence for the vortex state in the Fe 2 CoGe thin films. • Contour graph of FORC infers the formation of vortex state. • Vortex state ∼1 μm with in – plane curling of the magnetization using MFM phase analysis. • Realization of vortex state using MOKE and OOMMF simulations. We report on the evidence for the vortex state in the thin films of Fe 2 CoGe through first order reversal curves, magnetic force microscope, longitudinal magneto-optical Kerr effect and micro-magnetic simulations. Phase purity of the films confirmed through X-ray diffraction, which confirms the A2 type disorder Heusler alloy structure. Contour graph of first order reversal curves infers the formation of vortex state that is useful to understand magnetization reversal and switching process. We do observe the vortex state ∼1 μm with in – plane curling of the magnetization using magnetic force microscope phase analysis. We believe that realization of vortex state formation in Fe 2 CoGe thin films may cater applications in future magnetic data storage and microwave oscillators. [ABSTRACT FROM AUTHOR]

Off-axis electron holography experiments have been combined with micromagnetic simulations to study the remnant magnetic states of electrodeposited Co/Cu multilayered nanocylinders. Structural and chemical data obtained by transmission electron microscopy have been introduced in the simulations. Three different magnetic configurations such as an antiparallel coupling of the Co layers, coupled vortices, and a monodomain-like state have been quantitatively mapped and simulated. While most of the wires present the same remnant state whatever the direction of the saturation field, we show that some layers can present a change from an antiparallel coupling to vortices. Such a configuration can be of particular interest to design nano-oscillators with two different working frequencies. [ABSTRACT FROM AUTHOR]

• Uniaxial anisotropy, pseudo magnetic properties in Fe 2 NiGe Heusler alloy thin films. • The crest height and trough depth coefficients are 9.44 × 106 (A/m).mT and 8.76 × 106 (A/m).mT respectively. • FORC infers small switching field distribution and formation of vortex state. We report on the anisotropy, pseudo magnetic properties and formation of vortex state in Fe 2 NiGe thin films. From the torque measurements, estimated anisotropy constants K 1 and K 2 are found to be 4.47 × 103 J/m3 and −1.98 × 102 J/m3 respectively. Pseudo magnetic properties such as pseudo hysteresis work and pseudo remanence work infer that motion of domain wall in Fe 2 NiGe is rather smooth. The crest height and trough depth coefficient from the second stage of magnetization curves are estimated and are found to be 9.44 × 106 (A/m).mT and 8.76 × 106 (A/m).mT respectively. First order reversal curves infer switching field distribution is very small, which infers that less dislocations and more grain size. Indeed, the vortex state is evident from the contour graph of the first order reversal curves. We believe present results would be helpful for the future spintronic devices based on Heusler alloy thin films. [ABSTRACT FROM AUTHOR]

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]

Magnetic states of nickel nanogranular films were studied in two distinct structures of individual and agglomerated granules electrodeposited on n-type Si(1 1 1) surface from a modified Watts bath at a low pH of 2. Magnetic force microscopy and micromagnetic simulations revealed three-dimensional out-of-plane magnetic vortex states in stand-alone hemispherical granules and their arrays, and multi-domain patterns in large agglomerates and integrated films. Once the granules coalesce into small chains or clusters, the coercivity values increased due to the reduction of inter-granular spacing and strengthening of the magnetostatic interaction. Further growth leads to the formation of a continuous granulated film which strongly affected the coercivity and remanence. This was characterized by the domain wall nucleation and propagation leading to a stripe domain pattern. Magnetoresistance measurements as a function of external magnetic field are indicative of anisotropic magnetoresistance (AMR) for the continuous films electrodeposited on Si substrate. [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]