Magnetic Recording Research Articles

A novel magnet system—which enables uniformity of radial flux density by means of a parabolic yoke—applied in the Planck-Balance

Abstract A uniform magnetic flux density that is effective in the movement range of the coil is essential for accurate Kibble balance experiments. By utilizing Hopkinson’s law and Kirchhoff’s circuit laws, basic formulas have been derived, providing a method to calculate the magnetic flux density distribution in the airgap of a cylindrical magnet system. A parabolic outer contour of the inner yoke has been found to be a suitable solution to achieve uniformity. Experiments show, that this approach results in a relative change of magnetic flux density in the order of 3 ⋅ 10 − 4 per 8 mm movement range, using a magnet system with a mass of only 2.3 kg. Therefore, the system will be integrated into the upgraded version of PTB’s Planck-Balance—a compact variant of a Kibble balance—aiming for sub 1 ⋅ 10 − 6 accuracy level determination of the geometric factor. The solution described provides a comparatively easy means to design a cylindrical magnet system, using only one permanent magnet disc, without the use of complex simulation software.

Sub-millimeter propagation of antiferromagnetic magnons via magnon-photon coupling

For the realization of magnon-based current-free technologies, referred to as magnonics, all-optical control of magnons is an important technique for both fundamental research and practical applications. Magnon-polariton is a coupled state of magnon and photon in a magnetic medium, expected to exhibit magnon-like controllability and photon-like high-speed propagation. While recent studies have observed magnon-polaritons as modulation of incident terahertz waves, the influence of magnon-photon coupling on magnon propagation properties remains unexplored. This study aimed to observe the spatiotemporal dynamics of coherent magnon-polaritons through time-resolved imaging measurements. BiFeO3 was selected as the sample due to its anticipated strong coupling between magnons and photons. The observed dynamics suggest that antiferromagnetic magnons can propagate over long distances, up to hundreds of micrometers, through strong coupling with photons. These results enhance our understanding of the optical control of magnonic systems, thereby paving the way for terahertz opto-magnonics.

Behavior of magnetic systems of different dimensions in a magnetic field

Purpose. To investigate the influence of the magnetic field on the formation of structures in magnetic media of various dispersities. Methods. Experiments to study the dynamics of magnetic inclusions were carried out on a self-made installation in flat transparent cells by microscopy. The magnetic field was created by an electromagnet FL-1 connected to a power source. Magnetite particles of various sizes, as well as metal balls with a diameter of 0.5 mm, were studied as a magnetic medium. Video recording was performed using a MICMED WiFi 2000X 5.0 microscope. Results. The dynamics of magnetic inclusions in a viscous liquid medium under the influence of a magnetic field, as well as under conditions of mechanical shear effects, have been studied. The influence of the magnetic field strength on the growth rate of chain structures, as well as on the angle of deflection under shear action, has been studied. A theoretical interpretation of the observed phenomena is proposed. Conclusion. During the experiment, it was found that under the influence of a magnetic field, magnetic inclusions form chain structures. Their size, growth rate and dynamics depend on the physical parameters of the system and the external magnetic field. An intensive increase in the formation of chains of magnetic inclusions was detected at low and medium values of the magnetic field strength. An experimental dependence of the angle of deviation of chain structures from the equilibrium position on the magnetic field strength is obtained, which correlates with known theoretical data, on the basis of which a computational model is proposed. The results of the study can be used to visualize numerical calculations of the dynamics of dispersed systems under external influences.

Study of mass outflow rates from magnetized advective accretion disk around rotating black holes

We develop and discuss a model formalism to study the properties of mass outflows that are emerged out from a relativistic, magnetized, viscous, advective accretion flow around a rotating black hole. In doing so, we consider the toroidal component as the dominant magnetic fields and synchrotron process is the dominant cooling mechanism inside the accretion disk. With this, we self-consistently solve the coupled accretion-ejection governing equations in the steady state and obtain the shock-induced global inflow-outflow solutions in terms of the inflow parameters, namely plasma-β (=pgas /pmag, pgas and pmag being gas and magnetic pressures), accretion rates (ṁ) and viscosity (αB), respectively. Using these solutions, we compute the mass outflow rate (Rṁ, the ratio of outflow to inflow mass flux) and find that mass loss from the magnetized accretion disk continues to take place for wide range of inflow parameters and black hole spin (ak). We also observe that Rṁ strongly depends on plasma-β, ṁ, αB and ak , and it increases as the magnetic activity inside the accretion disk is increased. Further, we compute the maximum mass outflow rate (R max ṁ) by freely varying the inflow parameters and find that for magnetic pressure dominated disk, R max ṁ ~ 24% (~ 30%) for a k=0.0 (0.99). Finally, while discussing the implication of our model formalism, we compute the maximum jet kinetic power using R max ṁ which appears to be in close agreement with the observed jet kinetic power of several black hole sources.

Nonlinear electrodynamics for the vacuum of Dirac materials: Photon magnetic properties and radiation pressures

We investigate the magnetic properties of photons propagating through Dirac materials in a magnetic field, considering both vacuum and medium contributions. Photon propagation properties are obtained through a second-order expansion of nonlinear Euler-Heisenberg electrodynamics at finite density and temperature considering Dirac material parameters (Dirac fine structure constant, band gap, and Fermi velocity). Total magnetization (including electron and photon contributions) and photon-effective magnetic moment are computed. Observables such as photon energy density, radiation pressure, and Poynting vector are obtained by an average of components of the energy-momentum tensor. All quantities are expressed in terms of Lagrangian derivatives. Those related to the vacuum are valid for any value of the external magnetic field, and both the weak- and strong-field limits are recovered. We discuss some ideas of experiments that may contribute to testing in Dirac materials the phenomenology of the strong magnetic field in the quantum electrodynamic (QED) vacuum and how nonlinear corrections on the magnetization, radiation pressure, and birefringence are amplified up to 103 times QED corrections. Published by the American Physical Society 2024

Asymmetry, Gap Opening, and a High Accretion Rate on DM Tau: A Hypothesis Based on the Interaction of Magnetized Disk Wind with Planets

Over 200 protoplanetary disk systems have been resolved by the Atacama Large Millimeter/submillimeter Array (ALMA), and the vast majority suggest the presence of planets. The dust gaps in transition disks are considered evidence of giant planets sculpting gas and dust under appropriate disk viscosity. However, the unusually high accretion rates in many T Tauri stars hosting transition disks challenge this theory. As the only disk currently observed with high turbulence, the high accretion rate (∼10−8.3 M ⊙ yr−1) observed in DM Tau indicates the presence of strong turbulence within the system. Considering the recent theoretical advancements in magnetized disk winds are challenging the traditional gap-opening theories and viscosity-driven accretion models, our study presents a pioneering simulation incorporating a simplified magnetized disk wind model to explain the observed features in DM Tau. Employing multifluid simulations with an embedded medium mass planet, we successfully replicate the gap formation and asymmetric structures evident in ALMA Band 6 and the recent Karl G. Jansky Very Large Array 7 mm observations. Our results suggest that when magnetized disk wind dominates the accretion mode of the system, it is entirely possible for a planet with a medium mass to exist within the gap inside 20 au of DM Tau. This means that DM Tau may not be as turbulent as imagined. However, viscosity within the disk should also contribute a little turbulence to maintain disk stability.

Effect of Annealing Temperature on the Characterizations of Cobalt Ferrite Nanoparticles Synthesized via Co-precipitation

This study investigates the effect of annealing temperature on the structural and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles synthesized via the co-precipitation method. The results indicate that the annealing temperature significantly enhances the crystal size and quality, yielding well-defined, impurity-free CoFe2O4 crystals. Magnetic measurements reveal that both saturation magnetization (Ms) and coercivity (Hc) are improved with annealing. The nanoparticles exhibit a soft-magnetic, single-domain state up to an annealing temperature of 1200°C. They reach a critical size of 39.7 nm and begin transitioning to a multi-domain state. These findings highlight the crucial role of annealing temperature in optimizing the properties of CoFe2O4 nanoparticles for potential applications in magnetic recording media, magnetic resonance imaging, magnetic fluid hyperthermia, biosensors, drug delivery, and cell separation.

Rotating wireless power transfer: A new concept for wireless charging systems

Fast and safe charging are current concerns in relation to wireless charging of autonomous guided vehicles (AGVs). Wireless Power Transfer (WPT) is a capable solution and a replacement for conventional contact-based methods. However, resonant inductive and capacitive WPT topologies demand more power as the gap between transmitter and receiver pads increases. These structures, initially developed for electric vehicle applications, do not adequately optimize power transfer and power quality for the smaller surface areas of AGVs. In this paper, a novel topology for wireless charging concept is described and validated. This methodology has been named rotating WPT, with a primary side spinning neodymium magnet disc. The receiver pad is composed of a circular coil with ferrite U-cores. Calculations of the induced voltage over the rotating magnetic field resulted in 1.95 V at an operating frequency of 2.7 kHz. FEM simulation results show approximately 3 V, while laboratory experiments outputted 33 mV at 3.8 kHz. A sinusoidal waveform was observed from prototype, and power was successfully transferred to the receiver end, validating this proposed topology. This novel WPT system has no inverter, rectifier, nor compensation, decreasing reactive power, assembly costs and complexity while transferring power and enhancing power quality.© 2017 Elsevier Inc. All rights reserved.

Differentiating dilatons from the axions by their mixing with photons

The quanta of scalar fields like the dilaton (ϕ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi $$\\end{document}) of scale symmetry origin and those of pseudoscalar fields like the axion (ϕ′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi '$$\\end{document}) of Peccei–Quinn symmetry origin couple to di-photons through dimension-5 operators. In a magnetized medium (MM), they in principle can interact with the two transverse (A‖,⊥\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$A_{\\parallel ,\\perp }$$\\end{document}) and one longitudinal (AL\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$A_{L}$$\\end{document}) degree of freedom of photons (γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}) as long as the total spin is conserved. However, of ϕ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi $$\\end{document} and ϕ′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi '$$\\end{document}, only one interacts with AL\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$A_{L}$$\\end{document}. We found that the ambient external magnetic field B and media break the intrinsic Lorentz symmetry of the system affecting the dispersion relation of the propagating modes. The boost and the rotational symmetry along and around B are however the ones that are preserved. Invoking C, P, and T symmetries, we analyze the mixing dynamics of ϕγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi \\gamma $$\\end{document} and ϕ′γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi '\\gamma $$\\end{document} systems and the structural difference in their mixing pattern. It is noted that while the ϕγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi \\gamma $$\\end{document} mixing matrix is 3×3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3\ imes 3$$\\end{document}, the ϕ′γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi ^{\\prime }\\gamma $$\\end{document} is governed by a 4×4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$4\ imes 4$$\\end{document} mixing matrix. Using the exact solutions of both systems in MM, we estimate the strength of the electromagnetic (EM) signals available due to these interactions, which are found to be different in strength. We conclude by commenting on (a) the possibility of detecting this difference in polarimetric observables of the EM signal, (b) the implications of these different mixing patterns with respect to the minimum detectable signal for astrophysical observations, and (c) the variation in the energy of the dispersed photons of different polarization with the variation in B.

A Versatile C/Fe3O4/C Self‐Heating Electrode for Universal Application of Alternating Magnetic Fields in Electrocatalytic Hydrogen Production

AbstractThe high‐frequency alternating magnetic field (AMF) is considered as a fascinating heating treatment that provides a noninvasive solution to enhance the catalytic efficiency of electrocatalyst. However, practical applications of AMF in electrochemistry are primarily concentrated on magnetic mediums. To broaden its application into nonmagnetic catalysts, herein, a practicable method is reported by modifying the working electrode substrate with magnetic Fe3O4 nanoparticles (NPs), which serves as both substrate and self‐heating medium by virtue of its rapid and efficient magnetic heating effect associated with Néel relaxation triggered by external high‐frequency AMF, thus boosting the catalyst performance upon it. To verify it, Pt NPs and Pt single atoms (SAs), as two representative non‐magnetic catalyst, are selected for trials. The results, reveal that, when AMF is applied, Pt NPs@C/Fe3O4/C and Pt SAs@C/Fe3O4/C display remarkable enhancement of hydrogen evolution reaction magnetocurrent density respectively by ≈ 146% and ≈185%, whereas on unmodified bare glassy carbon there both show unnoticeable change in catalytic performance. The developed strategy opens up a vast space for exploiting the energy of a weak, non‐invasive magnetic field.

First-Principles investigations into electronic, magnetic, elastic, and optical phenomena in SmCrO3: Towards spintronic and magnetic storage applications

Using a thorough DFT analysis, this work investigates the electronic, magnetic, elastic, and optical phenomena in the cubic and orthorhombic phases of SmCrO3. The study explores the distinct qualities of both phases, such as their electronic features, magnetic behaviors, and elastic responses, using the GGA-PBE and mBJ-GGA-PBE methodologies. The study highlights the potential of SmCrO3 cubic and orthorhombic structures in spintronics and magnetic device applications by confirming their half-metallic nature. A deeper understanding of the electronic structure and magnetic stability of the materials results from the intricate interplay of spin effects and thorough investigation of magnetic interactions.

Numerical solutions of steady radiative Maxwell-nanofluid flow toward a stretching sheet in the presence of magnetic field and porous medium

The study investigates the behavior of a Maxwellian nanofluid flowing steadily over an extending sheet in a permeable medium with a magnetic field. The energy equation includes the radiation, and the conservation of momentum equation considers the magnetic field and porous medium. The novelty of this study is in its examination of complex phenomena involving magnetic fields, radiation, Maxwell fluids, and nanoparticle suspensions in a porous medium via an exponential stretching sheet. The study of Maxwell fluids has been enriched by the substantial contributions made by researchers, delving into their rheological behavior, modelling, and applications. Their work has provided valuable insights into the complexities of these materials and has advanced the knowledge in this specialized area of fluid mechanics. The governing partial differential equations (PDEs) are converted into ordinary differential equations (ODEs) utilizing an appropriate similarity transformation. These resultant ODEs are then resolved by employing a numerical approach, specifically the finite element method. The numerical simulations provide valuable information regarding the distributions of velocity, temperature, and nanoparticle concentration. Furthermore, the presented tabulated outcomes display alterations in skin friction, mass transfer rate, heat transmission coefficients, and their reliance on different emerging parameters. The velocity diminishes as the magnetic field, suction, Maxwell fluid, and medium factors increase, while it enhances with the stretching sheet limitation. The temperature diminishes with the Prandtl number but upsurges with higher radiation, thermophoresis, and Brownian motion. As the thermophoresis limit increases, concentration rises, but it decreases with an upsurge in the Lewis and Brownian motion. The heat transfer rate rises with radiation, thermophoresis, and Brownian motion, but the mass transfer rate decreases with Lewes and Brownian motion. The outcomes of the study could have implications for various engineering and industrial applications that control and manipulate fluid flows and heat transfer.

The Impementation of POE Learning Model (Predict Observe Explain) Assisted Magnet KIT to Improve Student Analitycal Thinking Skills

This research aims to measure students' level of analytical thinking in the Natural Sciences learning process about magnetism through the POE (Predict Observe Explain) learning model with the help of a magnetic KIT (Integrated Instrument Box). The research method applied is quantitative through a Quasi Experimental design. Research instruments include interviews, questionnaires, and posttests. The research subjects were control class IX.4 which participated in the conventional learning group and experimental group IX.5 which implemented a POE model with magnetic KIT media at MTs Hasanah Pekanbaru. Data was collected through a posttest of analytical thinking skills and analyzed using descriptive analysis and the Independent Sample T test. The analysis obtained shows a significant variation in average values in the experimental and control groups, in the POE group achieving a higher level of analytical thinking (67.16%) than the conventional class (55.16%). This shows the effectiveness of POE learning with the help of magnetic KIT in improving students' analytical thinking skills regarding the context of magnetic material.

Optomagnetism with a plasmonic skyrmion.

Research at the frontier between optics and magnetism is revealing a wealth of innovative phenomena and avenues of exploration. Optical waves are demonstrating the capacity to induce ultrafast magnetism, while optical analogs of magnetic states, such as magnetic skyrmions, offer the prospect of novel, to the best of our knowledge, spin-optical states. In this Letter, we strengthen the synergy between light and magnetism by exploring the ability of plasmonic Neel skyrmions to create an optomagnetic field, i.e., an opto-induced stationary magnetic field, within a thin gold film. We show that, when generated using a focused radially polarized vortex beam (RPVB), a plasmonic Neel skyrmion emerges as an optimum for inducing optomagnetism in a thin gold film. Optical skyrmions offer new degrees of freedom for enhancing and controlling optomagnetism in plasmonic nanostructures, with direct application in all-optical magnetization switching, magnetic recording, and the excitation of spin waves.

Two-phase separation facilitating the ordering of L10-FePt: experimental and thermodynamic investigation on Fe–Pt–Cu phase diagrams

The L10-FePt nanocrystals exhibit unique magnetic and catalytic properties, but suffer from the ordering difficulty. The addition of Cu can facilitate the L10-FePt ordering for some Fe–Pt–Cu alloys, however, the action mechanism is far from being well understood. In this work, a systematic study has been performed to the phase diagrams of the Fe–Pt–Cu system. The isothermal sections at 600 °C, 750 °C and 1000 °C, as well as the partial vertical sections of Fe50Pt50–Cu50Pt50 and Fe50Pt50–Cu, were constructed. An emphasis has been paid to the L10-FePt phase, which has a wide composition range with a solid solubility of Cu up to 40.0 at% at 600 °C. Its order-disorder transition temperature decreases rapidly when deviating from 54 at% Pt, but at different lower rates along (FePt)100-xCux and (Fe50-xCux)Pt50 with the increase of Cu. The ternary miscibility gap which originates from the Fe–Cu side has been studied by both experimental determinations and thermodynamic calculations. The results indicate that, at certain low temperatures, for instance 300 °C, the metastable miscibility gap can expand even up to 45 at% Pt, entering the L10-FePt phase region. An ordering transition mechanism of the L10-FePt phase stimulating by a two-phase separation was thus proposed. For a specially designed disordered Fe–Pt–Cu alloy, a metastable two-phase separation can take place firstly in the annealing process, driving the Cu atoms forming Cu-rich particles, leaving a large number of vacancies in the alloy, and consequently, accelerate the atomic diffusion and stimulate the subsequent L10 ordering transition. These results will provide a new perspective for the composition design of Fe–Pt–Cu catalysts and magnetic recording media.

Landau Tidal Damping and Major-Body Clustering in Solar and Extrasolar Subsystems

Major (exo)planetary and satellite bodies seem to concentrate at intermediate areas of the radial distributions of all the objects orbiting in each (sub)system. We show that angular-momentum transport during secular evolution of (exo)planets and satellites necessarily results in the observed intermediate accumulation of the massive objects. We quantify the ‘middle’ as the mean of mean motions (orbital angular velocities) when three or more massive objects are involved. Radial evolution of the orbits is expected to be halted when the survivors settle near mean-motion resonances and angular-momentum transfer between them ceases (gravitational Landau damping). This dynamical behavior is opposite in direction to what has been theorized for viscous and magnetized accretion disks, in which gas spreads out and away from either side of any conceivable intermediate area. We present angular momentum transfer calculations in few-body systems, and we also calculate the tidal dissipation timescales and the physical properties of the mean tidal field in planetary and satellite (sub)systems.

Field-free switching of perpendicular magnetization in a noncollinear antiferromagnetic Mn3Sn/[Pt/Co]4 heterostructure

Spin-orbit torque (SOT) manipulation of perpendicular magnetization is essential for realizing spintronic storage and logic devices. When a charge current flows through a heavy metal/ferromagnetic layer structure, a spin current can be generated by the heavy metal and injects into the ferromagnetic layer with perpendicular magnetic anisotropy and switch its magnetization via the SOT. However, in order to realize the deterministic switching, an in-plane external magnetic field is needed to break the inversion symmetry, a technological requirement that hampers the practical application of SOT. Pt/Co multilayer is a good magnetic recording media and, thus, the all-electric manipulation of its perpendicular magnetic moments is of practical significance. The noncollinear spin structure in Mn3Sn allows an unconventional spin polarization direction, and the associated SOT can switch the magnetic moments in the absence of an external field. In this work, we demonstrate the field-free SOT switching of a heterostructure utilizing Mn3Sn and Pt/Co multilayer as the spin source and the ferromagnetic layer with perpendicular magnetization, respectively. Our results are important for advancing the development of spintronic devices based on noncollinear antiferromagnets.

Using optical vortex laser induced forward transfer to fabricate a twisted ferrite microcrystal array

We demonstrate direct printing from donor ink containing ferrite nanoparticles by employing laser induced forward transfer with an optical vortex possessing orbital angular momentum (OAM). We show, for the first time, that the as-printed dots are twisted and exhibit spinel Fe3O4 monocrystalline properties without the need for a sintering process. The helicity of the as-printed dots is shown to be selectively controlled merely by reversing the handedness of optical vortices. The diameter of the printed dots was typically measured to be less than 1/10th of the irradiated laser spot (diffraction limit). These results imply that the optical vortex twists and confines the sintered nanoparticles within its dark core to form chiral spinel monocrystalline dots. The observation of mono-crystallization with optical vortex induced forward transfer will offer new fundamental physics such as OAM light–matter interactions and could pave the way toward advanced printable magnetic devices, such as high-density magnetic data storage.

Modeling the secular evolution of embedded protoplanetary disks

Context. Protoplanetary disks are known to form around nascent stars from their parent molecular cloud as a result of angular momentum conservation. As they progressively evolve and dissipate, they also form planets. While a lot of modeling efforts have been dedicated to their formation, the question of their secular evolution, from the so-called class 0 embedded phase to the class II phase where disks are believed to be isolated, remains poorly understood. Aims. We aim to explore the evolution between the embedded stages and the class II stage. We focus on the magnetic field evolution and the long-term interaction between the disk and the envelope. Methods. We used the GPU accelerated code IDEFIX to perform a 3D, barotropic, non ideal magnetohydrodynamic (MHD) secular core collapse simulation that covers the system evolution from the collapse of the pre-stellar core until 100 kyr after the first hydrostatic core formation and the disk settling while ensuring sufficient vertical and azimuthal resolutions (down to 10−2 au) to properly resolve the disk internal dynamics and non axisymmetric perturbations. Results. The disk evolution leads to a power-law gas surface density in Keplerian rotation that extends up to a few 10 au. The magnetic flux trapped in the disk during the initial collapse decreases from 100 mG at disk formation down to 1 mG by the end of the simulation. After the formation of the first hydrostatic core, the system evolves in three phases. A first phase with a small (∼10 au), unstable, strongly accreting (∼ 10−5 M⊙ yr−1) disk that loses magnetic flux over the first 15 kyr, a second phase where the magnetic flux is advected with a smooth, expanding disk fed by the angular momentum of the infalling material, and a final phase with a gravitationally regulated ∼60 au disk accreting at at few 10−7 M⊙ yr−1. The initial isotropic envelope eventually feeds large-scale vertically extended accretion streamers, with accretion rates similar to that onto the protostar (∼ 10−6 M⊙ yr−1). Some of the streamer material collides with the disk’s outer edge and produces accretion shocks, but a significant fraction of the material lands on the disk surface without producing any noticeable discontinuity. Conclusions. While the initial disk size and magnetization are set by magnetic braking, self-gravity eventually drives accretion, so that the disk ends up in a gravitationally regulated state. This evolution from magnetic braking to self-gravity is due to the weak coupling between the gas and the magnetic field once the disk has settled. The weak magnetic field at the end of the class I phase (Bz ∼ 1 mG) is a result of the magnetic flux dilution in the disk as it expands from its initial relatively small size. This expansion should not be interpreted as a viscous expansion, as it is driven by newly accreted material from large-scale streamers with large specific angular momentum.

In vivo magnetic recording of single-neuron action potentials Abbreviated title: In vivo magnetic single-neuron action potentials.

Measuring fast neuronal signals is the domain of electrophysiology and magnetophysiology. While electrophysiology is easier to perform, magnetophysiology avoids tissue-based distortions and measures a signal with directional information. At the macroscale, magnetoencephalography (MEG) is established, and at the mesoscale, visually evoked magnetic fields have been reported. At the microscale however, while benefits of recording magnetic counterparts of electric spikes would be numerous, they are also highly challenging in vivo. Here, we combine magnetic and electric recordings of neuronal action potentials in anesthetized rats using miniaturized giant magneto-resistance (GMR) sensors. We reveal the magnetic signature of action potentials of well-isolated single units. The recorded magnetic signals showed a distinct waveform and considerable signal strength. This demonstration of in vivo magnetic action potentials opens a wide field of possibilities to profit from the combined power of magnetic and electric recordings and thus to significantly advance the understanding of neuronal circuits.