Magnetic Foil Research Articles

Investigating magnetization of permanent magnets by magnetic flux viewing film

Permanent magnets are used in many current industrial as well as home appliances today. Frequently, kitchen plastic magnets could be found at the refrigerators at home. However, the magnetic domain structure of such permanent plastic foils is not known and understood to the users at all. The purpose of this paper is to explain the magnetic domain structure of plastic magnets with Halbach array and ferrite or neodymium magnet polarization orientation. Principles of magnetic field visualization foils (magnetic flux detector and colour changing viewing film) is explained and demonstrated on multipole magnetic structures. Experiments with magnetic polarization reversal by the strong neodymium magnet in weaker ferrite magnetic material is demonstrated. All presented principles are collected in the simple magnetic set and suggested for education of school children of different ages. Elementary school children below 10 years age are mostly interested only in making hidden pictures in magnetic paper and ferrite magnet. Older school children of 11–12 years are able to absorb more knowledge about behaviour and properties of magnets.

Experimental and Numerical Analysis of a Car Body Shield Loaded with a Ballistic Impact

This paper presents the possibility of using additional ballistic shields based on composite materials, which are applied to the body of a passenger car. A ballistic laminate made of Twaron T 750 aramid fabric with 5 mm thick and 2 mm thick magnetic foil was used. In the first stage, the mechanical parameters of the tested ballistic laminate system were determined in tensile tests. In field tests, the considered system was analyzed in terms of impact with a 9 × 19 mm FMJ Parabellum projectile, and then the results were numerically verified. The work was focused on the validation of numerical models. The appropriate correlation level of the numerical results was obtained with the fit, which was estimated at approximately 7%; furthermore, the results prove the correctness of this study’s research methodology.

Reactive laser ablation in acetone towards phase-controlled nonequilibrium Iron- and Nickel-Bi2O3 nanoalloys

The ongoing development of new nanocatalysts is powered by the ambitious vision of finely controlling their structure while ensuring their remarkable features in heterogeneous chemical reactions. Especially in processes where the catalysts must be recycled, the union of catalytic activity and magnetic motility belongs among the most desirable characteristics. In recent years, the effort to optimize this synergy in photocatalysis has led to a focus on creating bismuth-based bimetallic nanoparticles (NPs), also known as nanoalloys. Nevertheless, the optimization of their properties and sustainable development still need to be well-considered. Therefore, we herein present for the first time the synthesis of phase-controlled nickel-Bi2O3 and iron-Bi2O3 NPs, whose non-equilibrium composition is provided by the sustainable method known as reactive laser ablation in liquids (RLAL), resulting in a bandgap modification in both types of magnetic nanoalloys. In addition, the profound analyses of RLAL introduce the first report about the limitations and new perspectives of this relatively novel nanotechnology, in which the usage of chemically similar magnetic foils (iron and nickel) leads to extensively different NPs compositions and properties. Overall, these findings provide a groundwork for understanding the formation of non-equilibrium nanoalloys representing a rising generation of nanocatalysts.

Thermal analysis of oscillating thermomagnetic devices beyond the lumped approximation

The temperature (T) dependent magnetization of materials near the Curie temperature has been leveraged for thermomagnetic energy harvesting and thermal rectification. In these thermal devices, a translating shuttle containing a ferromagnet (e.g., gadolinium) experiences a T-dependent magnetic attraction to a stationary permanent magnet, leading to steady-periodic mechanical oscillations of the shuttle between the hot and cold surfaces. Prior analytical work investigating thermomagnetic devices has focused on the small-Biot (Bi) number regime in which the shuttle T is thermally lumped due to the small interfacial thermal contact conductances. Here, we use a separation of variables technique to derive analytical expressions to the governing heat conduction equation for the full spatiotemporal T profile considering a thin magnetic foil mounted on a thick shuttle. The results show that the lumped solution prediction for the time-averaged heat flow Q is accurate within <5% when either the hot or cold surface Bi is <0.1. In the moderate-to-large Bi regime, analytical solutions and numerical validations show that Q approaches a maximum value determined by conduction through the shuttle, while the oscillation frequency f increases with increasing Bi. The analytical solutions developed here can be used to design and evaluate the thermal performance of thermomagnetic devices proposed for use in energy scavenging and thermal rectification applications.

Accurate determination of the electron spin polarization in magnetized iron and nickel foils for Møller polarimetry

The Møller polarimeter in Hall A at Jefferson Lab in Newport News, VA, has provided reliable measurements of electron beam polarization for the past two decades. Past experiments have typically required polarimetry at the 1% level of absolute uncertainty which the Møller polarimeter has delivered. However, the upcoming proposed experimental program including MOLLER and SoLID have stringent requirements on beam polarimetry precision at the level of 0.4% (The MOLLER Collaboration, 2014; The SoLID collaboration, 2019), requiring a systematic re-examination of all the contributing uncertainties.Møller polarimetry uses the double polarized scattering asymmetry of a polarized electron beam on a target with polarized atomic electrons. The target is a ferromagnetic material magnetized to align the spins in a given direction. In Hall A, the target is a pure iron foil aligned perpendicular to the beam and magnetized out of plane parallel or antiparallel to the beam direction. The acceptance of the detector is engineered to collect scattered electrons close to 90° in the center of mass frame where the analyzing power is a maximum (-7/9).One of the leading systematic errors comes from determination of the target foil polarization. Polarization of a magnetically saturated target foil requires knowledge of both the saturation magnetization and g′, the electron g-factor which includes components from both spin and orbital angular momentum from which the spin fraction of magnetization is determined. Target foil polarization has been previously addressed in a 1997 publication “A precise target for Møller polarimetry” by de Bever et al. (1997) at a level of precision sufficient for experiments up to this point. Several shortcomings with the previous published value require revisiting the result prior to MOLLER. This paper utilizes the existing world data to provide a best estimate for target polarization for both nickel and iron foils including uncertainties in magnetization, high-field and temperature dependence, and fractional contribution to magnetization from orbital effects. We determine the foil electron spin polarization at 294 K to be 0.08020 ± 0.00018 (@4 T applied field) for iron and 0.018845±0.000053 (@2 T applied field) for nickel. We conclude with a brief discussion of additional systematic uncertainties to Møller polarimetry using this technique.

High-throughput nuclear resonance time domain interferometry using annular slits.

Nuclear resonance time domain interferometry (NR-TDI) is used to study the slow dynamics of liquids (that do not require Mössbauer isotopes) at atomic and molecular length scales. Here the TDI method of using a stationary two-line magnetized 57Fe foil as a source and a stationary single-line stainless steel foil analyzer is employed. The new technique of adding an annular slit in front of a single silicon avalanche photodiode detector enables a wide range of momentum transfers (1 to 100 nm-1 by varying the distance between the annular slits and sample) with a high count rate of up to 160 Hz with a Δq resolution of ±1.7 nm-1 at q = 14 nm-1. The sensitivity of this method in determining relaxation times is quantified and discussed. The Kohlrausch-Williams-Watts (KWW) model was used to extract relaxation times for glycerol. These relaxation times give insight into the dynamics of the electron density fluctuations of glycerol as a function of temperature and momentum transfers.

Absorption of microwaves by random-anisotropy magnets

Microscopic model of the interaction of spins with a microwave field in a random-anisotropy magnet has been developed. Numerical results show that microwave absorption occurs in a broad range of frequencies due to the distribution of ferromagnetically correlated regions on sizes and effective anisotropy. That distribution is also responsible for the weak dependence of the absorption on the damping. At a fixed frequency of the ac-field, spin oscillations are localized inside isolated correlated regions. Scaling of the peak absorption frequency agrees with the theory based upon the Imry-Ma argument. The effect of the dimensionality of the system related to microwave absorption by thin amorphous magnetic wires and foils has been studied.

Vortex particles in axially symmetric fields and applications of the quantum Busch theorem

The possibilities to accelerate vortex electrons with orbital angular momentum (OAM) to relativistic energies and to produce vortex ions, protons, and other charged particles crucially depend on whether the OAM is conserved during the acceleration and on how phase space of the wave packet evolves. We show that both the OAM and a mean emittance of the packet, the latter obeying the Schrödinger uncertainty relation, are conserved in axially symmetric fields of electric and magnetic lenses, typical for accelerators and electron microscopes, as well as in Penning traps. Moreover, a linear approximation of weakly inhomogeneous fields works much better for single packets than for classical beams. We analyze quantum dynamics of the packet’s rms radius ⟨ρ 2⟩, relate this dynamics to a generalized form of the van Cittert–Zernike theorem, applicable at arbitrary distances from a source and for non-Gaussian packets, and adapt the Courant–Snyder formalism to describe the evolution of the packet’s phase space. The vortex beams can therefore be accelerated, focused, steered, trapped, and even stored in azimuthally symmetric fields and traps, somewhat analogously to the classical angular-momentum-dominated beams. We also give a quantum version of the Busch theorem, which states how one can produce vortex electrons with a magnetized cathode during either field- or photoemission, as well as vortex ions and protons by using a magnetized stripping foil employed to change a charge state of ions. Spatial coherence of the packets plays a crucial role in these applications and we provide the necessary estimates for particles of different masses.

Simulations of foil-based spin-echo (modulated) small-angle neutron scattering with a sample using McStas.

For the further development of spin-echo techniques to label elastic scattering it is necessary to perform simulations of the Larmor precession of neutron spins in a magnetic field. The details of some of these techniques as implemented at the reactor in Delft are simulated. First, the workings of the magnetized foil flipper are simulated. A full virtual spin-echo small-angle neutron scattering instrument is built and tested without and with a realistic scattering sample. It is essential for these simulations to have a simulated sample that also describes the transmitted beam of unscattered neutrons, which usually is not implemented for the simulation of conventional small-angle neutron scattering (SANS) instruments. Finally, the workings of a spin-echo modulated small-angle neutron scattering (SEMSANS) instrument are simulated. The simulations are in good agreement with theory and experiments. This setup can be extended to include realistic magnetic field distributions to fully predict the features of future Larmor labelling elastic-scattering instruments. Configurations can now be simulated for more complicated combinations of SANS with SEMSANS.

Trapping laser pulse between two foils and periodic generation of energetic electron beam

When an intense right-hand circularly polarized laser pulse propagates through a highly magnetized (in the direction of laser propagation) foil into the vacuum region between this foil and an unmagnetized foil, it can be multiply reflected and thus quasitrapped between the two foils until its energy is depleted. During the multiple reflections at the magnetized foil, foil electrons are accelerated by the laser light. Electrons that have gained sufficient energy can escape and appear as periodic energetic electron bunches at a time interval determined precisely by the trapping time or the distance between the two foils.

Large magnetoelectric coupling in 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3) TiO3 film on Ni foil

Lead-free, high piezocoefficient 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 film is fabricated on soft magnetic Ni foil as a substrate using a pulse laser deposition technique for the magnetoelectric studies. The x-ray diffraction analysis confirms the phase pure formation of polycrystalline ferroelectric film along with the presence of NiO formed during the high temperature growth process. The obtained lattice parameters suggest that the native oxide could favour the coherent growth of a ferroelectric layer. The film exhibits ferroelectric characteristics with a polarization value of 23 µC cm−2 at 225 kV cm−1. The fabricated heterostructure displayed a high magnetoelectric coupling coefficient with the maximum magnetoelectric voltage coefficient (α31) value of 1.08 V cm−1 Oe−1 at low field of 44 Oe. It is noteworthy to mention that the observed α31 is comparable to the earlier reported toxic lead-based similar systems. The comparison between the experimental and calculated α31 values suggests that the strain transfer percentage efficiency is around 69%, which is responsible for the observed large ME coupling. These experimental findings give a way to achieve high magnetoelectric coefficients by fabricating the oxide piezoelectric layer directly on the clamping free magnetic substrate.

A Faraday effect magnetic stripe scanner

We report on the realization of a Faraday magnetometer to characterize the magnetization of a magnetic foil during its production process at full speed of 3 m/s. The system is designed towards attaining a spatial resolution both in feeding direction and transverse to it of approximately 60 μm and is able to acquire in excess of 60.000 scan lines per second obtained from a line-scan camera with 128 pixels. We further report on the resolution of this system regarding the magnitude of the magnetization of the stripe and contrast this to the attainable noise figure determined by the optical properties of the used crystal, the illumination system and the camera.

Interpretation of increased energetic particle flux measurements by SEPT aboard the STEREO spacecraft and contamination

Context. Interplanetary (IP) shocks are known to be accelerators of energetic charged particles observed in-situ in the heliosphere. However, the acceleration of near-relativistic electrons by shocks in the interplanetary medium is often questioned. On 9 August 2011 a corotating interaction region (CIR) passed STEREO B (STB), which resulted in a flux increase in the electron and ion channels of the Solar Electron and Proton Telescope (SEPT). Because electron measurements in the few keV to several 100 keV range rely on the so-called magnet foil technique, which is utilized by SEPT, ions can contribute to the electron channels. Aim. We aim to investigate whether the flux increase in the electron channels of SEPT during the CIR event on 9 August 2011 is caused by ion contamination only. Methods. We compute the SEPT response functions for protons and helium utilizing an updated GEANT4 model of SEPT. The CIR energetic particle ion spectra for protons and helium are assumed to follow a Band function in energy per nucleon with a constant helium to proton ratio. Results. Our analysis leads to a helium to proton ratio of 16.9% and a proton flux following a Band function with the parameters I0 = 1.24 × 104 (cm2 s sr MeV nuc−1)−1, Ec = 79 keV nuc−1, and spectral indices of γ1 = −0.94 and γ2 = −3.80, which are in good agreement with measurements by the Suprathermal Ion Telescope (SIT) aboard STB. Conclusions. Since our results explain the SEPT measurements, we conclude that no significant amount of electrons were accelerated between 55 and 425 keV by the CIR.

Analysis of Ultra-Thin and Flexible Current Transformer Based on &lt;italic&gt;JA&lt;/italic&gt; Hysteresis Model

This paper describes the design, fabrication, and analysis of an ultra-thin and highly flexible current sensing transformer. The transformer windings are printed on flexible polyimide substrate layers with a magnetic foil sandwiched in between. The fabricated transformer can wrap around any electrical cable for current sensing purpose. The design of the transformer adopts a circuit model that includes the nonlinearity of the magnetic core based on the Jiles–Atherton hysteresis model, which is validated experimentally.

Nondestructive Evaluation Using a High-&lt;italic&gt;T&lt;/italic&gt;cSQUID Microscope

We report the application of a scanning high- $T_{{\rm{c}}}$ SQUID (superconducting quantum interference device) microscope with a ferromagnetic flux guide for the nondestructive evaluation of weld seams and wear tracks and scars on austenitic stainless steel plates as well as measurement of magnetic stray fields distribution above patterned by electron lithography 30-nm-thick cobalt films. A soft magnetic amorphous Vitrovac foil was used to guide the flux from the samples, which were held at room temperature, to the liquid-nitrogen-cooled SQUID-sensor and back. The flux guide passes through a hole in the $\text{1 mm}\times \text{2.5 mm}$ pick-up loop of the high- $T_{{\rm{c}}}$ SQUID sensor, thereby providing improved coupling of the magnetic flux from the object to the SQUID. In order to avoid the influence of the SQUID biasing the magnetic field on the object under investigation, a modulation and feedback coil was coupled to the pick-up loop of the SQUID directly and beyond the ferromagnetic flux guide. Such decoupling of feedback coil from soft magnetic flux antenna ensures that the high- $T_{{\rm{c}}}$ SQUID microscope does not disturb the sample magnetization during image recording. The SQUID microscope can be used to measure the spatial distribution of the z -component of the stray field above a specimen without mechanical contact to it.

Process analysis and optimization for fracture stress of electron beam welded ultra-thin FeCo-V foils

Generally, the quality of a weld joint is directly influenced by the welding parameter settings. In order to obtain a weld metal with desired weld bead quality and profile, it is necessary to adjust suitable process parameters in welding instrument. In this work, numerical and graphical optimization techniques of the electron beam welding of ultra-thin FeCo-V magnetic foils were carried out using response surface methodology (RSM) based on central composite design. The procedure was established to improve the weld strength and increase the productivity by considering the welding parameters range of beam current (0.7–1.7 mA), beam voltage (40–50 kV), welding speed (150–500 mm/min), and focused position (−20 to 0 mm). Tensile test and microhardness measurements were employed in order to study the mechanical behaviors of the welds. Moreover, microstructural observation and phase analysis were carried out in order to elucidate the change mechanism of mechanical properties in the welded area. It was found that RSM can be considered as a powerful tool in experimental welding optimization, even when the experimenter has not a model for the process. Strong, efficient, and acceptable weld joints could be achieved using the optimum welding conditions.

Vibration control of high-speed rotor supported by hybrid foil-magnetic bearing with sudden imbalance

A hybrid foil-magnetic bearing (HFMB) was successfully studied as a vibration isolator by introducing a sudden imbalance or an unexpected disturbance during turbine/rotor operation. This HFMB is used to achieve stability during transient vibration behavior. The HFMB consists of two oil-free bearing technologies: an active magnetic bearing (AMB) and air foil bearing (AFB). Using both technologies takes advantage of the strengths of each bearing while compensating for their inherent weaknesses. In addition, the HFMB has good dynamic characteristics, and the damping can be adjusted using the appropriate gain selection for the AMB controller. Based on these unique features, dynamic stability can be enhanced, even if a sudden imbalance occurs while the rotor is operating. In this study, a rigid rotor was operated at up to 12,000 rpm and tested using a control algorithm to reduce the sudden imbalance vibration amplitudes. The experiment was conducted under the situation that the mass dropped out at 6,000 rpm. In order to validate the stability performance of the HFMB with a sudden mass loss, the vibration response results for the AFB and HFMB were compared. When applying the HFMB, the asynchronous vibration was suppressed, and the 1x vibration results showed reductions of almost 30%. When the sudden mass loss occurred, the magnetic control force was remarkably effective at reducing the asynchronous vibration of the rotor supported by the HFMB. In conclusion, it was experimentally verified that using the HFMB made sudden imbalance vibration control possible during rotor operation with an air foil bearing. In this respect, the HFMB has the characteristics of high stiffness/damping, which prevent rubbing and suppress excessive vibration due to a sudden imbalance event.

Magnetised foils as white beam π/2 flippers for polarised neutrons

Magnetic foils as white beam π/2 flippers for polarised neutrons will be discussed. Their main advantage is the application for Larmor precession in strongly inclined precession regions as used in Larmor diffraction and especial in Spin Echo Small Angle Neutron Scattering (SESANS). Inclination angles of a few degrees in fields from mT up to hundreds of mT are achievable that are not possible with present conventional coils. The application in Larmor diffraction will be discussed and the application in SESANS will be explained in detail and supported by a simulated experiment.

On the nonlinear steady-state response of rigid rotors supported by air foil bearings—Theory and experiments

The demand for oil-free turbo compressors is increasing. Current trends are divided between active magnetic bearings and air foil bearings (AFB), the latter being important due to mechanical simplicity. AFB supported rotors are sensitive to unbalance due to low damping and nonlinear characteristics, hence accurate prediction of their response is important. This paper gives theoretical and experimental contributions by implementing and validating a new method to simulate the nonlinear steady-state response of a rotor supported by three pads segmented AFBs. The fluid film pressures, foil deflections and rotor movements are simultaneously solved, considering foil stiffness and damping coefficients estimated using a structural model, previously described and validated against experiments.

Beam-induced heat load in in-vacuum undulators with a small magnetic gap

For hard X-rays users in a synchrotron radiation source, the development of an in-vacuum mini-gap undulator with a short period is a recent trend. The performance of the undulator can become degraded by large beam-induced heat load that arises from both the synchrotron radiation (SR) and the image current. SR is responsible for avalanche meltdown of the magnet foil, whereas the image current mainly decreases the threshold of power to cause an avalanche meltdown. To maximize the performance of the in-vacuum undulator, we hence consider the most appropriate conditions for the beam in a storage ring, such as a long bunch length or a small bunch current. An appropriate strategy to utilize the undulator is also important, for example, operating a collinear double in-vacuum undulator or a canted in-vacuum undulator with a small canting angle may result in avalanche meltdown of the magnet foil.In this paper, we present methods to calculate the linear power density of SR and the resistive wall heating on a conductive magnet foil. The beam-induced heat load of a double undulator in Taiwan Photon Source (TPS) is presented as an example.