Homogeneous Magnetic Field Research Articles

Inhomogeneous field calibration of a magneto-optical indicator film device

A concept for the traceable calibration of magneto-optical indicator film (MOIF) based magnetic field imaging devices is presented and discussed for the example of a commercial MOIF device with a 60 × 45 mm2 sensor. The calibration facilitates a quantitative and fast characterization of magnetic microstructures combining relatively high spatial resolution with large imaging areas. The macroscopic calibration is performed using the homogeneous magnetic stray field of a pre-characterized electromagnet with a large pole shoe diameter of 250 mm. However, this calibration alone cannot yet account for the vectorial and spatially fast decaying stray fields of magnetic microstructures. For that, a forward simulation approach is pursued, based on the temperature-dependent magnetic parameters of the MOIF material as resulting from superconducting quantum interference device magnetometry and ferromagnetic resonance measurements. This is complemented by a transfer function-based approach to correct the impact of the sensor thickness and in-plane stray field components. The validity of the combined calibration and simulation approach is proven by means of a quantitative characterization of a magnetic scale. For the commercial MOIF device a 28.4 µm spatial resolution and 1.18 mT field resolution is achieved. The calibration is validated by a comparison to scanning Hall probe microscopy results. Furthermore, the uncertainty budget is discussed.

Thermodynamics of quantum phase transitions of a Dirac oscillator in a homogenous magnetic field

The Dirac oscillator in a homogeneous magnetic field exhibits a chirality phase transition at a particular (critical) value of the magnetic field. Recently, this system has also been shown to be exactly solvable in the context of noncommutative quantum mechanics featuring the interesting phenomenon of re-entrant phase transitions. In this work we provide a detailed study of the thermodynamics of such quantum phase transitions (both in the standard and in the noncommutative case) within the Maxwell–Boltzmann statistics pointing out that the magnetization has discontinuities at critical values of the magnetic field even at finite temperatures.

Investigation of engineering properties of steel fiber reinforced concrete exposed to homogeneous magnetic field

The present study was performed to investigate the effect of applying homogeneous magnetic field (HMF) of density 0.5 Tesla (T) to steel fiber reinforced concrete (SFRC) specimens containing 1.5% volume of fiber on engineering properties. To achieve this goal, compressive and flexural strengths tests were employed to evaluate mechanical properties of the SFRC specimens at the age of 28 days. Furthermore, durability characteristic of the specimens was investigated for water absorption and permeable porosity tests. The non-destructive test based on ultrasonic pulse velocity (UPV) was used to assess the compressive strength of the specimens exposed to the HMF applied to either fresh or hardened states. In order to generate HMF, a magnetic device capable of causing the intended intensity was designed and manufactured. The concrete tests results indicated that the applying HMF to the SFRC specimens, during the casting process, increased their mechanical strength in the terms of compressive and flexural strengths to 18 and 16%, respectively. Also, flexural toughness of the specimens was enhanced by 7% compared to the specimen with no magnetic treatment. Due to the HMF exposure to the SFRC specimens, water absorption and permeable porosity values of the specimens decreased by 11 and 18%, respectively.

Screening corrections to electron capture rates and resulting constraints on primordial magnetic fields

We explore screening effects arising from a relativistic magnetized plasma with applications to Big Bang nucleosynthesis (BBN). %Specifically, due to their small magnetic moments, energies of electrons and positrons can be easily quantized via Landau quantization. The screening potential which depends on the thermodynamics of charged particles in the plasma is altered by the magnetic field. We focus on the impact of screening on the electron capture interaction. Taking into account the correction in BBN arising from a homogeneous primordial magnetic field (PMF), we constrain the epoch at which the PMF was generated and its strength during BBN. Considering such screening corrections to the electron capture rates and using up-to-date observations of primordial elemental abundances, we also discuss the possibility of solving the problem of under-estimation of the deuterium abundance. We find for certain values of the PMF strength predicted D and $^4$He abundances are both consistent with the observational constraints.

Importance of Basset History Force for the Description of Magnetically Driven Motion of Magnetic Particles in Air

Abstract Lungs are used as an attractive possibility for administration of different therapeutic substances for a long time. An innovative method of such administration widely studied nowadays is the application of aerosolized magnetic particles as the carriers to the lungs in the external non-homogeneous magnetic field. For these reasons we have studied dynamics of such a system on a level of particle trajectory in air in the presence of magnetic force as a driving force exerted on micrometric magnetic particle. On two typical examples of magnetically driven systems—motion of magnetic particle in a gradient magnetic field and cyclotron-like motion of a charged particle in homogeneous magnetic field in microscale, where the external accelerating forces are very large and the relevant time scale is of the order from fraction of milliseconds to seconds, we have examined the importance of these forces. As has been shown, for particles with high initial acceleration, not only the commonly used Stokes force but also the Basset history force should be used for correct description of the motion.

GALACTIC COSMIC RAY ANISOTROPY MODELLING

We calculate the angular distribution of cosmic rays at a given point of the heliosphere under the assumption that the incoming flux from outer space is isotropic. The static magnetic field is shown to cause no anisotropy provided that the observation point is situated out of the trapped particle area. We consider a coronal ejection model in the form of a static cylinder with an axial homogeneous magnetic field inside. We calculate angular distribution samples in the trapped particle area (inside the cylinder) and show that there is a certain cone of directions with a reduced flux. For the same model with the moving cylinder, the angular distribution samples are calculated for different positions of the observation point outside the cylinder. Anisotropy of order of the ejection to light velocity ratio is shown to arise. The calculated samples are in qualitative agreement with URAGAN muon hodoscope data.

Holomorphic quantum Hall states in higher Landau levels

Eigenstates of the planar magnetic Laplacian with a homogeneous magnetic field form degenerate energy bands, the Landau levels. We discuss the unitary correspondence between states in higher Landau levels and those in the lowest Landau level, where wave functions are holomorphic. We apply this correspondence to many-body systems; in particular, we represent effective Hamiltonians and particle densities in higher Landau levels by using corresponding quantities in the lowest Landau level.

Моделирование анизотропии галактических космических лучей

We calculate the angular distribution of cosmic rays at a given point of the heliosphere under the assumption that the incoming flux from outer space is isotropic. The static magnetic field is shown to cause no anisotropy provided that the observation point is situated out of the trapped particle area. We consider a coronal ejection model in the form of a static cylinder with an axial homogeneous magnetic field inside. We calculate angular distribution samples in the trapped particle area (inside the cylinder) and show that there is a certain cone of directions with a reduced flux. For the same model with the moving cylinder, the angular distribution samples are calculated for different positions of the observation point outside the cylinder. Anisotropy of order of the ejection to light velocity ratio is shown to arise. The calculated samples are in qualitative agreement with URAGAN muon hodoscope data.

Homogenous nuclear magnetic resonance probe using the space harmonics suppression method

Abstract. Nuclear magnetic resonance imaging (MRI) has became an unavoidable medical tool in spite of its poor sensitivity. This fact motivates the efforts to enhance the nuclear magnetic resonance (NMR) probe performance. Thus, the nuclear spin excitation and detection, classically performed using radio-frequency coils, are required to be highly sensitive and homogeneous. The space harmonics suppression (SHS) method, already demonstrated to construct coil producing homogenous static magnetic field, is used in this work to design radio-frequency coils. The SHS method is used to determine the distribution of the electrical conductive wires which are organized in a saddle-coil-like configuration. The theoretical study of these SHS coils allows one to expect an enhancement of the signal-to-noise ratio with respect to saddle coil. Coils prototypes were constructed and tested to measure 1H NMR signal at a low magnetic field (8 mT) and perform MRI acquired at a high magnetic field (3 T). The signal-to-noise ratios of these SHS coils are compared to the one of saddle coil and birdcage (in the 3 T case) of the same size under the same pulse sequence conditions demonstrating the performance enhancement allowed by the SHS coils.

Magnetoconductance, Quantum Hall Effect, and Coulomb Blockade in Topological Insulator Nanocones.

Magnetotransport through cylindrical topological insulator (TI) nanowires is governed by the interplay between quantum confinement and geometric (Aharonov-Bohm and Berry) phases. Here, we argue that the much broader class of TI nanowires with varying radius-for which a homogeneous coaxial magnetic field induces a varying Aharonov-Bohm flux that gives rise to a nontrivial masslike potential along the wire-is accessible by studying its simplest member, a TI nanocone. Such nanocones allow us to observe intriguing mesoscopic transport phenomena: While the conductance in a perpendicular magnetic field is quantized due to higher-order topological hinge states, it shows resonant transmission through Dirac Landau levels in a coaxial magnetic field. Furthermore, it may act as a quantum magnetic bottle, confining surface Dirac electrons and leading to a largely interaction-dominated regime of Coulomb blockade type. We show numerically that the above-mentioned effects occur for experimentally accessible values of system size and magnetic field, suggesting that TI nanocone junctions may serve as building blocks for Dirac electron optics setups.

Single-Molecule Toroic Design through Magnetic Exchange Coupling

Summary Toroidal molecular magnets represent promising candidates for next-generation ultra-dense information storage. These wheel-like molecules are able to store one bit per molecule because of their insensitivity to homogeneous magnetic fields—one of the main sources of magnetic perturbations. However, synthesis of molecules possessing a well-defined and stable vortex arrangement of the on-site magnetic moments in the ground state represents a challenge. Here, we show that 16 magnetic metal ions can be alternately arranged into a macrocycle named {Fe8Dy8}. The net toroidal moment can be experimentally determined at 0.23 Tesla. Moreover, ab initio calculations were performed to reveal that ferromagnetic exchange interactions between the FeIII and DyIII metal centers are the key to generate this toroidal moment. This feature is significantly distinguished from the previously described dipole-dipole interaction-based single-molecule toroics (SMTs), showing the importance of exchange-coupling interactions in the design of next-generation SMTs.

Measuring the Kelvin-Helmholtz instability, stabilized by a tangential magnetic field

In a flow channel we experimentally investigate the stability of the interface between a laminar flow of diamagnetic fluid, and a layer of ferrofluid, resting on top of it. This interface is locally perturbed by means of a bar oscillating with a driving frequency. Measuring the growth rate of the interfacial waves, we explore the stabilizing effect of a homogeneous magnetic field oriented in flow direction. A zero growth rate determines the critical flow velocity. The latter increases with the applied magnetic field and depends sensitively on the driving frequency. The results are described in part by an established, simple inviscid model.

Design and realization of a sputter deposition system for the in situ and in operando use in polarized neutron reflectometry experiments: Novel capabilities

Recently, the design and realization of a sputter-deposition system for in situ and in operando polarized neutron reflectometry (PNR) was reported. The device allows magnetic thin films and heterostructures to be grown, while the sample remains aligned in the neutron beam for PNR. By now, it has been applied in experiments that investigated the magnetic and structural properties of thin Fe and Pd/Fe/Pd heterostructures as a function of the layer thickness. Here, we report on significant upgrades of the deposition system with advanced thin film growth and measurement capabilities. These include improvements to the generation of the vacuum to realize ultra-high-vacuum (UHV) conditions. A base pressure below 5 × 10−9mbar can now be obtained within less than one day of pumping time. To allow experiments over a wide range of temperatures, the system was upgraded to include a cryo-furnace. It allows the sample to be cooled or heated in the range of 10K to 1000K for both applications, sample growth and measurement. Further, a new magnetic coil setup with soft iron yoke was designed which can realize a homogeneous in-plane magnetic field of up to 300mT and electric fields at the sample position.

Quantum Acoustomechanics with a Micromagnet.

We show theoretically how to strongly couple the center-of-mass motion of a micromagnet in a harmonic potential to one of its acoustic phononic modes. The coupling is induced by a combination of an oscillating magnetic field gradient and a static homogeneous magnetic field. The former parametrically couples the center-of-mass motion to a magnonic mode while the latter tunes the magnonic mode in resonance with a given acoustic phononic mode. The magnetic fields can be adjusted to either cool the center-of-mass motion to the ground state or to enter into the strong quantum coupling regime. The center of mass can thus be used to probe and manipulate an acoustic mode, thereby opening new possibilities for out-of-equilibrium quantum mesoscopic physics. Our results hold for experimentally feasible parameters and apply to levitated micromagnets as well as micromagnets deposited on a clamped nanomechanical oscillator.

Volume metasolenoid-based coil for 23Na MRI at 7 Tesla

In this work, we demonstrate a novel X-nuclei radiofrequency coil design aimed for ultra-high field magnetic resonance imaging. The proposed design is based on a set of coupled split-loop resonators, forming a so-called metasolenoid, fed via inductive coupling by a non-resonant loop. Due to the fundamental mode excitation in the metasolenoid the homogeneous RF magnetic field inside its inner volume is provided. 23Na RF coil for human wrist imaging at 7 Tesla based on the proposed approach is demonstrated and investigated numerically. The design is compared with a commercially available volume birdcage coil. The comparative study revealed 60% improvement of SAR efficiency of metasolenoid coil operating in the linearly-polarized mode over the birdcage coil driven in the circularly polarized mode.

The Thermal Teleportation of a Qutrit in the Two-qutrits xxz chain

We study the effect of temperature, magnetic field and Dzyaloshinskii-Moriya interaction on the fidelity of thermal teleportation in the xxz two-qutrits Heisenberg chain. We observe that the fidelity is an increasing function of temperature, but a decreasing function of the strength of the Dzyaloshinskii-Moriya interaction. Moreover, as the positive homogeneous magnetic field is increased, the fidelity is finally vanished. If the negative homogeneous magnetic field is increased, at first, the fidelity decreases but eventually follows an almost straight line. Increasing positive and negative inhomogeneous magnetic field causes the fidelity to increase.

The impact of magnetic field on the conformations of supracolloidal polymer-like structures with super-paramagnetic monomers

We investigate the properties of magnetic supracolliodal polymers -- magnetic filaments (MFs) -- with super-paramagnetic monomers, with and without Van der Waals (VdW) attraction between them. We employ molecular dynamics (MD) simulations to elucidate the impact of crosslinking mechanism on the structural and magnetic response of MFs to an applied external homogeneous magnetic field. We consider two models: plain crosslinking, which results in a flexible backbone; and constrained crosslinking, which provides significant stiffens against bending. We find that for plain crosslinking, even a slight increase of the central attraction leads to collapsed MF conformations. Structures that initially exhibit spherical symmetry evolve into cylindrically symmetric ones, with growing magnetic field strength. Plain crosslinking also allows for conformational bistability. MFs with constrained crosslinking tend to, instead, unravel in field. In both crosslinking scenarios, central attraction is able to hinder low-field magnetic response of MFs, albeit the bistability of plainly crosslinked MFs manifests itself also in the high-field region.

An Optimal Design of an Electromagnetic Actuation System towards a Large Homogeneous Magnetic Field and Accessible Workspace for Magnetic Manipulation

Untethered nano-/microrobots have been appealing to biomedical applications under magnetic guidance. Numerous actuation systems are specifically designed to generate either uniform or non-uniform fields which are unable to support all actuating mechanisms of magnetic robots. The size of their accessible space does not enable applications in life sciences (e.g., placing around human parts for tasks or an in vivo experiment in animals). Moreover, homogeneity of uniform magnetic fields is limited in a small region. Here, we propose an electromagnetic coil system that is optimally designed based on numerical simulation investigations to derestrict the mentioned constraints. The built-up system provides a large bore in which magnetic field generation by passing a 10 A current is strong enough for nano-/micromanipulation switchable between uniformity in a large-homogeneous region about 50-mm-wide along the x- and y-axes and 80-mm-wide along the z-axis, and with a non-uniformity of about 12 mT with 100 mT/m. It experimentally carries out potential and versatile controls to manipulate several commonly used microrobots that require a particular type of magnetic field to perform multi-DOF locomotion in diverse viscous environments. (e.g., helical propulsion by rotating magnetic field in the 3D-large workspace and in the complex network path, side-to-side sweeping-slip locomotion by oscillating fields, translation and rocking-slip locomotion by gradient-based fields). Besides, the system can be reproduced into any accessible space size regarding the square coil size to support diverse applications and guarantee the result in both uniformity of magnetic field in the large homogeneous region and a sufficiently strong gradient over the workspace.

Numerical study of the homogeneous and inhomogeneous magnetic field effects on the plasma‐based radar cross‐section reduction

A numerical method based on the recursive convolution finite difference time domain was used to calculate the radar cross-section (RCS) of a square target under different conditions. The results indicate that for electron number density below , unmagnetised plasma provides better RCS reduction compared to magnetised plasma. For this range of electron density, the wave bending plays an important role and its effect is stronger than the resonant and non-resonant absorption. For densities higher than , and for collision frequencies less than plasma frequency, magnetised plasma causes greater RCS reduction compared to unmagnetised plasma due to strong resonant absorption. In this situation, the inhomogeneous magnetic field is preferred because of its broader bandwidth. The enhanced bandwidth is due to multi-resonance absorption of the inhomogeneous magnetic field. For collision frequencies above the plasma frequency, resonance absorption weakens and non-resonance absorption prevails. Then in this range of plasma parameters, the unmagnetised plasma is the proper choice for optimum RCS reduction.

Schwarzschild spacetime immersed in test nonlinear electromagnetic fields

Kerr black hole immersed in test, asymptotically homogeneous magnetic field, aligned along the symmetry axis, is described by Wald’s solution. We show how the static case of this solution may be generalized for nonlinear electromagnetic models via perturbative approach. Using this technique we find the lowest order correction to Wald’s solution on Schwarzschild spacetime in Euler–Heisenberg and Born–Infeld theories. Finally, we discuss the problem of highly conducting star in asymptotically homogeneous magnetic field.