Stray Magnetic Field Research Articles

Surface engineering of magnetic and mechanical properties of Ta/Pt/GdFeCo/IrMn/Pt heterostructures by femtosecond laser pulses

Irradiation of the heterostructure glass/Ta/Pt/GdFeCo/IrMn/Pt by 50 fs ultra-short laser pulses causes local thinning of the film down to ~12–30 nm depth. These pits are distinguished by Atomic Force Microscopy (AFM), while their stray magnetic fields were detected by Magnetic Force Microscopy (MFM). The crater was formed due to layer- by -layer evaporation of the material. No sign of melting was found in the vicinity of the crater at subthreshold laser fluence below 12–15 mJ/cm2, but exceeding of the threshold caused destruction of the layers. Energy-dispersive X-ray spectroscopy (EDX) revealed depletion of Gd, Fe and Co, responsible for magnetic properties of the subthreshold crater. The amplitude of the local MOKE signal decreased down to 1.7 times in the irradiated area, while thinning of the ferromagnetic layer was 1.1 times. No proportional change of magnetization was caused by bias effect of IrMn layer. Decreased elastic modulus was found inside the subthreshold crater in the irradiated areas. Laser engineering of the surface of GdFeCo thin films opens the way for local control of energy balance between magnetic anisotropy, exchange coupling and Zeeman energy and creation of separated sectors for capture, storage and analysis of the ferromagnetic nanoparticles.

Ferromagnet/Superconductor Hybrid Magnonic Metamaterials.

In this work, a class of metamaterials is proposed on the basis of ferromagnet/superconductor hybridization for applications in magnonics. These metamaterials comprise of a ferromagnetic magnon medium that is coupled inductively to a superconducting periodic microstructure. Spectroscopy of magnetization dynamics in such hybrid evidences formation of areas in the medium with alternating dispersions for spin wave propagation, which is the basic requirement for the development of metamaterials known as magnonic crystals. The spectrum allows for derivation of the impact of the superconducting structure on the dispersion: it takes place due to a diamagnetic response of superconductors on the external and stray magnetic fields. In addition, the spectrum displays a dependence on the superconducting critical state of the structure: the Meissner and the mixed states of a type II superconductor are distinguished. This dependence hints toward nonlinear response of hybrid metamaterials on the magnetic field. Investigation of the spin wave dispersion in hybrid metamaterials shows formation of allowed and forbidden bands for spin wave propagation. The band structures are governed by the geometry of spin wave propagation: in the backward volume geometry the band structure is conventional, while in the surface geometry the band structure is nonreciprocal and is formed by indirect band gaps.

Mini-ants manage vision miniaturisation

Miniaturisation doesn't seem to be a problem for Ant-Man when he climbs into his suit and shrinks, but the mini-superhero could face challenges he hadn't bargained for. For example, water and air become super sticky at microscopic scales and tiny creatures lose heat faster than bulkier bodies. But what effect does being small have on vision and the way that mini-beasts see the world? Does shrinking the eye affect how much detail an animal can see and how well objects stand out from the background? Intrigued by the question, Ajay Narendra from Macquarie University, Australia, turned to Ant-Man's namesakes. ‘Quantifying this in ants was really a no-brainer’, he chuckles, pointing out that ants rely heavily on vision and they vary enormously in size. But, most importantly, there were hordes of different species right on Narendra's doorstep.Choosing to investigate the vision of ants ranging in size from massive bull ants (Myrmecia tarsata) to medium-sized jack jumpers (Myrmecia nigrocincta), and tiny spiny ants (Polyrhachis nr aurea) and Rhytidoponera inornata, Ravindra Palavalli-Nettimi and Yuri Ogawa braved the insects’ vicious stings, bringing a handful back to the lab. Cautiously painting clear nail varnish over the insects’ eyes, Palavalli-Nettimi and Ogawa produced almost perfect minute casts of the structures to measure the lens size and number. Not surprisingly, the eyes of the biggest bull ants had the largest (∼22 μm wide) – and highest number of (∼2627) – lenses, while the middle-sized jack jumpers squeezed a similar number (∼2483) of smaller lenses into their eyes. Meanwhile, both of the smaller ant species had far fewer lenses, with the eyes of the tiny R. inornata containing only ∼227 minute lenses, averaging 12.75 μm across. But how well could the ants see in practice?Knowing that Laura Ryan and Nathan Hart had recently developed a technique that allowed them to assess how clearly sharks see – by measuring minute voltage changes in the eye – Palavalli-Nettimi and Ogawa adapted the method to record how well the ants could see flickering black and white bars as the duo varied the bar thickness and how well they stood out from the background. ‘The most challenging task was to obtain a good signal-to-noise ratio in the smallest ant’, says Palavalli-Nettimi, who resorted to shielding the delicate ant eyes from stray electric and magnetic fields with a Faraday cage so he could record the weak voltages.Amazingly, when the team eventually compared the ants’ eyesight, the minute R. inornata could see almost as clearly as the heftiest M. tarsata bull ants. ‘The smallest ants had only 8% of the facets [lenses] of the largest ants, but had 80% of their spatial resolution’, says Narendra. And, when the team compared how well objects stand out for the differently sized insects, the heavyweight bull ants had the upper hand, able to pick out faint objects that were only 6.4% brighter than their background, in contrast to the diminutive R. inornata ants, which could only distinguish objects that were 74.1% brighter. ‘This shows that smaller ants place more emphasis on spatial resolving power than contrast sensitivity’, says Narendra. However, when the team compared how long the insects’ eyes took to respond when a light flicked on, the smaller ants response time was ∼260 ms, in contrast the bull ants’ speedy ∼106 ms, ‘which may allow them [R. inornata] to improve their contrast sensitivity’, says Narendra.So, the eyesight of mini-ants is poorer than that of their outsized cousins, but not as weak as their size difference might suggest, and Narendra is keen to see how other insect species deal with the challenge of miniaturisation.

High-Contrast Quantum Imaging with Time-Gated Fluorescence Detection

Optical detection of spin state has been widely used for the solid state spin qubit in the application of quantum information processing. The signal contrast determines the accuracy of quantum state manipulation, sensitivity of quantum sensing and resolution of quantum imaging. Here, we demonstrated a time-gated fluorescence detection method for enhancing the spin state signal contrast of nitrogen vacancy (NV) center in diamond. By adjusting the delay between time gate and the excitation laser pulse, we improved both the signal contrast and signal-to-noise ratio for NV spin detection. An enhancement ratio of 1.86 times was reached for the signal contrast. Utilizing the time-gated fluorescence detection, we further demonstrated a high contrast quantum imaging of nanoparticle's stray magnetic field. Without any additional manipulation of the quantum state, we expect that this method can be used to improve the performance of various applications with NV center.

Development of a miniaturized rotational electromagnetic energy harvester with a liquid metal direct-write process

This research proposes a new method for producing micro-coils, which are used in a rotational power generator. A self-developed liquid metal forming system is used to produce a micro-coil that has a low roughness surface, is conductive, and has plane and out-of-plane wiring. For the coil size design, simulation is used to predict the feasibility of using the stray magnetic field to increase induction power generation. The coil is then integrated with a multi-pole NdFeB magnet and applied to an eccentric mass action rotational power generator. Environmental rotational power is converted by rotational machinery and electromagnetic conversion to produce inductive voltage and generate power. The experimental results show that the packaged generator is ∅22 mm ×12 mm thick in size and can output 120 mV at a rotational speed of 3.9 krpm. The output power is 20.3 μW. The power is stored in a super capacitor to realize an independent micro power generation device.

Fully 3D-Printed, Monolithic, Mini Magnetic Actuators for Low-Cost, Compact Systems

We report the design, fabrication, and experimental characterization of the first fully 3D-printed, multi-material miniature magnetic actuators for compact systems in the literature. The actuator design integrates a bonded hard magnet made of NdFeB microparticles embedded in a Nylon 12 matrix (55% by volume) with structural and support elements made of pure Nylon 12. The device is a 10 mm-diameter, 1.2 mm wall-thick, and 9 mm tall cylindrical frame that mounts on an off-the-shelf solenoid and a 10 mm diameter, 100 $\mu \text{m}$ -thick, leak-tight membrane connected at its center to a 4 mm diameter, 4.95 mm tall hard magnet. The actuators are monolithically printed in layers as thin as $100~\mu \text{m}$ using $600~\mu \text{m}$ -wide strokes via fused filament fabrication (FFF) –a low-cost 3D printing technology capable of processing high-performance thermoplastics to create monolithic objects made of a plurality of distinctive feedstock. The average surface roughness, Young’s modulus, and hardness of the FFF-printable hard-magnetic filament were estimated at $58.55~\mu \text{m}$ , 3.59 GPa, and Shore D 71.5, respectively, while the average surface roughness, Young’s modulus, and yield strength of FFF-printed magnetic material were estimated at $5.79~\mu \text{m}$ , 2.02 GPa, and 55.99 MPa ± 4.59 MPa, respectively. Magnetic characterization of the FFF-printed NdFeB-embedded Nylon 12 feedstock demonstrates the fabrication of isotropic hard magnets with an intrinsic coercivity of ~700 kA/m, remanence of ~395 mT, and a maximum energy product of 27 kJ/ $\text{m}^{3}$ . Simulations of the stray magnetic field produced by a printed sample made of NdFeB-embedded Nylon 12 were validated using a scanning Hall probe. The vertical displacement of a miniature 3D-printed magnetic actuator was characterized with a solenoid for various coil bias voltages; a maximum displacement equal to 50 $\mu \text{m}$ was obtained with 3.1 V DC applied to the driving coil. Finite element simulations of the actuator design estimate at 2.38 MPa the maximum stress on the membrane at $50~\mu \text{m}$ actuation (i.e., below the fatigue limit of Nylon 12), and at 592.61 Hz the natural frequency of the device, which was corroborated via experiment. [2018-0288]

Circuit Models and Fast Optimization of Litz Shield for Inductive-Power-Transfer Coils

The metal shields with plates or rings are usually added to the inductive-power-transfer coils to attenuate the stray magnetic field. However, the coil-to-coil efficiency is reduced owning to the extra losses on the shields. This paper introduces the litz shield which attenuates the field with smaller shielding loss thanks to the uniform distribution of the shield current. Two types of litz shields, i.e., shorted litz shield and driven litz shield are discussed in detail. Their performances are analyzed with the circuit model composed of four coupled inductors. The efficiency and the field attenuation for the coils with litz shields are optimized with Pareto fronts. A fast method to derive the fronts using a lumped-loop model is described. Only tens of finite-element simulations are required in the entire optimization. The coils with different shields were optimized to transfer 100-W power across 40-mm gap with the same efficiency. The measurement results prove that the shorted litz shield is more effective than the other shields. It attenuated 23% more of the stray magnetic field compared to the coils with traditional metal shield.

Magnetic Field Effect on Anodic Dissolution of Axle Steel in Bicarbonate Solution with Chlorides

The vehicle axle in the railway locomotive is a very important component. Localized corrosion is a cause of its degradation. Localized corrosion is usually caused by corrosive environments especially in media containing chloride ions. Harmonic currents in the power supply loops (contact nets and guide rails) of the train during train travel can produce stray current that produces stray magnetic fields. Some studies have shown that magnetic fields can accelerate or inhibit localized corrosion of metals. In this study, optical microscopy (OM) and electrochemical measurements were used to study the effects of magnetic field on the electrochemical behavior and corrosion morphology of axle steel in sodium bicarbonate solutions with and without chloride ions. Different scan rates were used in the measurements of anodic polarization curves. Potentiostatic polarization measurements were performed with applying or removing a 0.4 T magnetic field. The surface morphologies of the electrodes were observed after potentiostatic polarization. Figure 1 show that, for axle steel in 0.05 mol/L NaHCO3 with or without 0.001 mol/L NaCl, the magnetic field increased the peak current, positively shifted the potential for the onset of passivation, and narrowed the passivation range. Chlorides increased the anodic current in the transpassivation region. The synergistic effect of magnetic field and chlorides on breakdown of passivation was more significant at high potential scan rate for the anodic polarization curve measurements. Obvious corrosion pits could be found after polarization, according to the morphology of the axle steel after polarization at a scan rate of 50 mV/min. It is found that the magnetic field significantly accelerated the corrosion. For axle steel in 0.05 mol/L NaHCO3 system, the potentiostatic polarization was carried out at -0.3 V(SCE). The current density decreased with increasing the polarization time. The current decreasing rate was mitigated by applying a 0.4T magnetic field, i.e., the anodic current density tended to be more stable under applied magnetic field, showing a significant magnetic field effect on anodic dissolution and pitting behavior of axle steel in this environments. Figure 1

Ballistic rectification based on inhomogeneous magnetic stray fields

We present a ballistic rectification effect in an orthogonal four-terminal cross junction where the symmetry is broken by local magnetic fields. The input current is injected between opposing branches and the current-free branches serve as potential probes. The local magnetic field is induced by two permalloy (Py) stripes with a magnetic single-domain structure, where one end of each stripe is positioned close to the junction center. The Py stripes are oriented such that an external in-plane magnetic field can magnetize them into two different main configurations having either equally or oppositely magnetized ends. Equal magnetic ends are expected to result in a Hall-effect device, while for opposite magnetic ends, the stray field should deflect the electrons into the same output lead for both current polarities, leading to a rectifying behavior. Here, we present the proof of concept for stray-field controlled transfer characteristics. First, we show by magnetic force microscopy that both configurations are stable and the Py stripes exhibit a remanent magnetic single-domain structure. Second, we demonstrate the influence of the remanent magnetization on the low-temperature dc characteristics which are superimposed by a parasitic background. Third, we present the extracted Hall and the rectified voltage which are, respectively, linearly and parabolically dependent on the input current up to ±55 μA.

An integrated magnetic microfluidic chip for rapid immunodetection of the prostate specific antigen using immunomagnetic beads.

The authors describe an integrated microfluidic chip for immunodetection of the prostate specific antigen (PSA) by using giant magnetoimpedance (GMI) sensor. This chip contains an immunoreaction platform and a biomarker detection system. The immunoreaction platform contains anincubation chamber anda reactive chamber to implement immunological reaction in microfluidics. The system can detect PSA rapidly with ultra-high sensitivity. Both are fabricated by MEMS technology. Immunomagnetic beads (If PSA binds to its antibody (that islabeled with immunomagnetic beads; IMBs)it will be trapped on the surface of self-assembled film. Trapped IMBs generatea stray magnetic field under the magnetization of the external applied magnetic field and can be detected by theGMI sensor. The chip can detect PSA with a detection limit as low as 0.1ng ∙ mL-1 and works in the 0.1ng ∙ mL-1 to 20ng ∙ mL-1concentration range. Compared to established GMI biosensors, the magnetic microfluidic chip reduces assay time, and lends itself to fast detection. It also avoids complex handling steps, enhances reaction efficiency and decreases experimental errors. Graphical abstract An integrated magnetic microfluidic chip which contains immunoreaction platform and biomarker detection system was designed and microfabricated by micro-electromechanical systems (MEMS) technology to detect prostate specific antigen (PSA) rapidly, and has promise in Point-of-care (PoC) diagnostic applications.

Superfluid spin transport in ferro- and antiferromagnets

This paper focuses on spin superfluid transport, observation of which was recently reported in antiferromagnet Cr$_2$O$_3$ [Yuan et al., Sci. Adv. 4, eaat1098 (2018)]. This paper analyzes the role of dissipation in transformation of spin current injected with incoherent magnons to a superfluid spin current near the interface where spin is injected. The Gilbert damping parameter in the Landau-Lifshitz-Gilbert theory does not describe dissipation properly, and the dissipation parameters are calculated from the Boltzmann equation for magnons scattered by defects. The two-fluid theory is developed similar to the two-fluid theory for superfluids. This theory shows that the influence of temperature variation in bulk on the superfluid spin transport (bulk Seebeck effect) is weak at low temperatures. The scenario that the results of Yuan et al. are connected with the Seebeck effect at the interface between the spin detector and the sample is also discussed. The Landau criterion for an antiferromagnet put in a magnetic field is derived from the spectrum of collective spin modes. The Landau instability starts in the gapped mode earlier than in the Goldstone gapless mode, in contrast to easy-plane ferromagnets where the Goldstone mode becomes unstable. The structure of the magnetic vortex in the geometry of the experiment is determined. The vortex core has the skyrmion structure with finite magnetization component normal to the magnetic field. This magnetization creates stray magnetic fields around the exit point of the vortex line from the sample, which can be used for experimental detection of vortices.

Magnetic Testing of Stressed State of Hydrotested Gas-Separator Wall

The stressed state of a hydrotested gas separator has been studied by magnetoelastic demagnetization. Correlation dependences are obtained between the level of magnetoelastic demagnetization of a complex-loaded gas-separator wall and the magnitude of hoop, meridian, and equivalent stresses it experiences. The magnetoelastic demagnetization of a residually magnetized test-object wall, loaded with internal pressure, was estimated from the change in the strength of its magnetic stray field measured along the normal (Hn) and tangent (Hτ) to the surface. It has been established that the growth of mechanical stresses in the separator wall to half the value of the yield strength of steel it is made of causes a noticeable irreversible decrease in the normal (Hn) and tangential (Hτ) components of the strength of its magnetic stray field in the residually magnetized area. It is shown that the method of magnetoelastic demagnetization has the highest sensitivity to mechanical stresses and is easiest to implement and most prompt compared with coercimetry and tensometry.

The stray magnetic fields in Magnetic Resonance Current Density Imaging (MRCDI)

PurposeMR Current Density Imaging (MRCDI) involves weak current-injection into the head. The resulting magnetic field changes are measured by MRI. Stray fields pose major challenges since these can dominate the fields caused by tissue currents. We analyze the sources and influences of stray fields. MethodsFirst, we supply validation data for a recently introduced MRCDI method with an unprecedented noise floor of ∼0.1 nT in vivo. Second, we assess the accuracy limit of the method and our corresponding cable current correction in phantoms ensuring high signal-to-noise ratio (SNR). Third, we simulate the influence of stray fields on current flow reconstructions for various realistic experimental set-ups. Fourth, we experimentally determine the physiological field variations. Finally, we explore the consequences of head positioning in an exemplary head coil, since off-center positioning provides space for limiting cable-induced fields. ResultsThe cable correction method performs well except near the cables. Unless correcting for cable currents, the reconstructed current flow is easily misestimated by up to 45% for a realistic experimental set-up. Stray fields dominating the fields caused by tissue currents can occur, e.g. due to a wire segment 20 cm away from the imaged region, or due to a slight cable misalignment of 3°. The noise is increased by 40% due to physiological factors. Minor patient movements can cause field changes of ∼40 nT. Off-centered head positioning can locally reduce SNR by e.g. 30%. ConclusionsQuantification of stray fields showed that MRCDI requires careful field correction. After cable correction, physiological noise is a limiting factor.

The potential science and engineering value of samples delivered to Earth by Mars sample return

The potential science and engineering value of samples delivered to Earth by Mars sample return

Nonreciprocal superposition state in antiferromagnetic optospintronics

The absence of net magnetization, which forbids any stray magnetic fields, is one of the greatest advantages of antiferromagnets in device applications. In conventional antiferromagnets, however, spin current cannot be extracted without the aid of a static magnetic field. Here, we develop a theory of antiferromagnetic opto-spintronics to resolve this fundamental dilemma. By coupling a linearly polarized photon and nonreciprocal magnon bands, we construct a superposition state of left- and right-handed magnon states with opposite group velocities. We numerically demonstrate that by using this superposition state, an antiferromagnetic spin current can be efficiently generated without a net magnetic field including net magnetization. We also find that the breakdown of the superposition state induces the stripe superfluid phase of a two-component Bose-Einstein condensate. Our results lay the foundation for manipulating the superposition states of emergent particles in devices.

Diamond Magnetic Microscopy of Malarial Hemozoin Nanocrystals.

Magnetic microscopy of malarial hemozoin nanocrystals is performed by optically detected magnetic resonance imaging of near-surface diamond nitrogen-vacancy centers. Hemozoin crystals are extracted from Plasmodium falciparum–infected human blood cells and studied alongside synthetic hemozoin crystals. The stray magnetic fields produced by individual crystals are imaged at room temperature as a function of the applied field up to 350 mT. More than 100 nanocrystals are analyzed, revealing the distribution of their magnetic properties. Most crystals (96%) exhibit a linear dependence of the stray-field magnitude on the applied field, confirming hemozoin’s paramagnetic nature. A volume magnetic susceptibility of 3.4 × 10−4 is inferred with use of a magnetostatic model informed by correlated scanning-electron-microscopy measurements of crystal dimensions. A small fraction of nanoparticles (4/82 for Plasmodium falciparum–produced nanoparticles and 1/41 for synthetic nanoparticles) exhibit a saturation behavior consistent with superparamagnetism. Translation of this platform to the study of living Plasmodium-infected cells may shed new light on hemozoin formation dynamics and their interaction with antimalarial drugs.

Characterization and optimization of ultra slow muon beam at J-PARC/MUSE: A simulation study

Abstract We have been developing an ultra slow muon microscope on the Super-omega muon beamline, called U-line, at the Muon Science Establishment (MUSE), Japan Proton Accelerator Research Complex (J-PARC), Japan. This development is expected to aid studies on nanoscience and three-dimensional visualization of small samples. During commissioning of the ultra slow muon beam, we performed Monte Carlo simulations, the results of which pointed out the significant effect of a stray magnetic field at the muonium chamber on the beam profile at sample position. To minimize this effect, we steered the beam using imbalance tuning of electric quadrupoles . This paper presents the simulation study of beam transportation, optimization, and characterization in terms of beam size, time, and energy distribution at sample position in one of the experimental areas, namely, U1A.

DETERMINATION OF HARDENED METAL LAYER THICKNESS USING MAGNETIC METHOD

The routine method to control metal surface layer is Vickers hardness test method. The existing nondestructive testing methods are based on measuring induction density and other magnetic quantities in magnetizer core. This causes the method error and restricts the ability to determine the structure of the processed material. The paper provides theoretical and experimental investigation of the method for controlling the hardened axis layer parameters by analyzing characteristics of stray magnetic field of the axis magnetized local surface area before and after rouletting. A method is proposed for determining the hardened metal layer thickness of the rolling stock axis, based on measuring the parameters of the magnetized local area stray magnetic field before and after processing. To justify the proposed method, mathematical modeling of stray magnetic field of the axis local magnetized section is performed before and after processing. Inspection for the hardened metal layer is performed using magnetization of the axis local segment with electromagnet, followed by measuring the stray magnetic field strength. The maximum value of the horizontal magnetic force is determined, which is an informative parameter. A mathematical model is developed for the magnetized section magnetic field, the results of numerical and field experiments are presented. The discrepancy between the experimental data and the results of theoretical calculations is estimated. The method makes it possible to control the thickness of the hardened metal layer and the quality of the hardening of the rolling stock axis.

Study on use of superconducting magnet and first inelastic neutron scattering experiment under magnetic field at 4SEASONS spectrometer

Magnets are important for studying magnetism and are commonly used as sample environment devices of neutron scattering instruments. However, the use of magnets was prevented at the time-of-flight direct-geometry neutron spectrometer 4SEASONS in Materials and Life Science Experimental Facility (MLF) at J-PARC, because the instrument is surrounded by iron components, and it is equipped with a piece of equipment operated with magnetic bearings. In the present work, we investigate the influence of stray magnetic fields from a superconducting magnet which is shared among neutron scattering instruments in MLF. Based on the investigation, we modified 4SEASONS such that it can be used with the magnet. Finally, we successfully performed the first inelastic neutron scattering experiments with applied magnetic fields using this sample environment.

Uniaxial Dynamical Decoupling for an Open Quantum System.

Dynamical decoupling (DD) is an active and effective method for suppressing decoherence of a quantum system from its environment. In contrast to the nominal biaxial DD, this work presents a uniaxial decoupling protocol that requires a significantly reduced number of pulses and a much lower bias field satisfying the "magic" condition. We show this uniaxial DD protocol works effectively in a number of model systems of practical interest, e.g., a spinor atomic Bose-Einstein condensate in stray magnetic fields (classical noise), or an electron spin coupled to nuclear spins (quantum noise) in a semiconductor quantum dot. It requires only half the number of control pulses and a 10-100 times lower bias field for decoupling as normally employed in the above mentioned illustrative examples, and the overall efficacy is robust against rotation errors of the control pulses. The uniaxial DD protocol we propose shines new light on coherent controls in quantum computing and quantum information processing, quantum metrology, and low field nuclear magnetic resonance.