Large Magnetic Field Research Articles

Giant nonlinear Faraday rotation in iron doped CdMnTe

Polarization rotation is an important parameter in the design of passive and active photonic components (optical isolators, magneto-optical valves, and magnetic field sensors). This effect is particularly important in materials with delocalized electrons and large atomic orbital moments like CdMnTe, which is an excellent candidate due to its large Zeeman splitting that gives rise to large Faraday rotation. In this paper we report a giant intensity dependent nonlinear Faraday rotation in iron doped Cd0.85Mn0.15Te:Fe crystal. Rotation on the order of 12o in magnetic field of the order of 0.55 T and intensities of 1.832 GW/cm2 can be achieved in a 1.9 mm thick sample. This is 60 time larger in magnitude than previously reported values. In large magnetic field, this intensity dependent rotation will be able to compete with two photon absorption in large magnetic fields, and enhance the linear faraday rotation.

Self-Biased Magneto-Electric Antenna for Very-Low-Frequency Communications: Exploiting Magnetization Grading and Asymmetric Structure-Induced Resonance.

VLF magneto-electric (ME) antennas have gained attention for their compact size and high radiation efficiency in lossy conductive environments. However, the need for a large DC magnetic field bias presents challenges for miniaturization, limiting portability. This study introduces a self-biased ME antenna with an asymmetric design using two magneto materials, inducing a magnetization grading effect that reduces the resonant frequency during bending. Operating principles are explored, and performance parameters, including the radiation mechanism, intensity and driving power, are experimentally assessed. Leveraging its excellent direct and converse magneto-electric effect, the antenna proves adept at serving as both a transmitter and a receiver. The results indicate that, at 2.09 mW and a frequency of 24.47 kHz, the antenna has the potential to achieve a 2.44 pT magnetic flux density at a 3 m distance. A custom modulation-demodulation circuit is employed, applying 2ASK and 2PSK to validate communication capability at baseband signals of 10 Hz and 100 Hz. This approach offers a practical strategy for the lightweight and compact design of VLF communication systems.

Magnetic field amplification in cosmological zoom simulations from dwarf galaxies to galaxy groups

ABSTRACT Magnetic fields are ubiquitous in the Universe. Recently, cosmological simulations of galaxies have successfully begun to incorporate magnetic fields and their evolution in galaxies and their haloes. However, so far they have mostly focused on Milky Way-like galaxies. Here, we analyse a sample of high-resolution cosmological zoom simulations of disc galaxies in haloes with mass ${M}_\rm {200c}$ from $10^{10}$ to $10^{13}\, \rm {M}_\odot$, simulated with the Auriga galaxy formation model. We show that with sufficient numerical resolution the magnetic field amplification and saturation is converged. The magnetic field strength reaches equipartition with turbulent energy density for galaxies in haloes with ${M}_\rm {200c}\gtrsim 10^{11.5}\, \mathrm{M_\odot }$. For galaxies in less massive haloes, the magnetic field strength saturates at a fraction of equipartition that decreases with decreasing halo mass. For our lowest mass haloes, the magnetic field saturates significantly below 10 per cent of equipartition. We quantify the resolution we need to obtain converged magnetic field strengths and discuss our resolution requirements also in the context of the IllustrisTNG cosmological box simulations. We show that, at z = 0, rotation-dominated galaxies in our sample exhibit for the most part an ordered large-scale magnetic field, with fewer field reversals in more massive galaxies. Finally, we compare the magnetic fields in our cosmological galaxies at z = 0 with simulations of isolated galaxies in a collapsing halo set-up. Our results pave the way for detailed studies of cosmic rays and other physical processes in similar cosmological galaxy simulations that crucially depend on the strength and structure of magnetic fields.

Alexei Alekseevich Abrikosov. 25 June 1928—29 March 2017

A. A. Abrikosov was a consummate theoretical physicist whose work permeates modern quantum many-body physics. His greatest impact is the explanation of a regime of superconductivity in large magnetic fields, where the field penetrates the superconductor in quantized vortices, but the superconducting properties persist. For this work he won the 2003 Nobel Prize (together with V. L. Ginzburg ForMemRS and A. J. Leggett FRS). This is the framework for practical uses of superconductivity for high-field magnets, used for example in magnetic resonance imaging, magnetically levitating trains and the Large Hadron Collider. The ‘Abrikosov lattice’ of quantized vortices is a precursor to more recent understandings of two-dimensional magnetism, and topological materials whose properties are defined by quantized currents. He provided the earliest understanding of resummation of singularities in quantum theories, co-authored a textbook that has trained generations of theorists and led major research institutes and programmes in the USSR and the USA.

Vector meson polarisation in heavy-ion collisions at the LHC

Heavy quarks, i.e. charm and beauty, are produced in the initial stage of heavy-ion collisions, on a time scale shorter than the medium formation time, and are sensitive to the large initial magnetic field produced perpendicular to the reaction plane, defined by the impact parameter direction and beam direction, in non-central heavy-ion collisions. In the presence of a large initial magnetic field, the charm quark can be polarised. The quark polarisation is then expected to be transferred to the hadron in the hadronisation process. We will present the first measurement of D*+ polarisation in Pb–Pb collisions at √SNN = 5.02 TeV, exploiting the large data sample collected by the ALICE Collaboration during the LHC Run 2 and we will compare these new results with the existing J/ψ polarisation measurements.

Neutrinos and Gamma Rays from Galaxy Clusters Constrained by the Upper Limits of IceCube

Clusters of galaxies possess the capability to accelerate cosmic rays (CRs) to very high energy up to ∼1018 eV due to their large size and magnetic field strength, which favor CR confinement for cosmological times. During their confinement, they can produce neutrinos and γ-rays out of interactions with the background gas and photon fields. In recent work, Hussain et al. have conducted three-dimensional cosmological magnetohydrodynamical simulations of the turbulent intracluster medium combined with multidimensional Monte Carlo simulations of CR propagation for redshifts ranging from z ∼ 5 to z = 0 to study the multimessenger emission from these sources. They found that when CRs with a spectral index in the range 1.5–2.5 and cutoff energy Emax=1016–1017 eV are injected into the system, they make significant contributions to the diffuse background emission of both neutrinos and γ-rays. In this work, we have revisited this model and undertaken further constraints on the parametric space. This was achieved by incorporating the recently established upper limits on neutrino emission from galaxy clusters, as obtained by the IceCube experiment. We find that for CRs injected with spectral indices in the range 2.0–2.5, cutoff energy Emax=1016–1017 eV, and power corresponding to (0.1–1)% of the cluster luminosity, our neutrino flux aligns with the upper limits estimated by IceCube. Additionally, the resulting contribution from clusters to the diffuse γ-ray background remains significant with values of the order of ∼10−5 MeV cm−2 s−1 sr−1 at energies above 500 GeV.

Relativistic dissipative magnetohydrodynamics from the Boltzmann equation for 2-particle species gas

We derive the equations of motion of relativistic magnetohydrodynamics from the Boltzmann equation using the method of moments. We consider a locally electrically neutral system composed of two particle species with opposite charges, with vanishing dipole moment or spin, so that the fluid has vanishing magnetization and polarization. We find that the dynamics of this fluid changes dramatically in the presence of a magnetic field. The shear stress tensor no longer adheres to a single differential equation; instead, it splits into three non-degenerate components, each evolving according to distinct dynamical equations. Exploring these equations in a Bjorken flow scenario, we find that for large magnetic fields, our theory predicts oscillatory behavior beyond the scope of an Israel-Stewart-like theory.

Spinon Heat Transport in the Three-Dimensional Quantum Magnet PbCuTe_{2}O_{6}.

Quantum spin liquids (QSLs) are novel phases of matter which remain quantum disordered even at the lowest temperature. They are characterized by emergent gauge fields and fractionalized quasiparticles. Here we show that the sub-kelvin thermal transport of the three-dimensional S=1/2 hyperhyperkagome quantum magnet PbCuTe_{2}O_{6} is governed by a sizeable charge-neutral fermionic contribution which is compatible with the itinerant fractionalized excitations of a spinon Fermi surface. We demonstrate that this hallmark feature of the QSL state is remarkably robust against sample crystallinity, large magnetic field, and field-induced magnetic order, ruling out the imitation of QSL features by extrinsic effects. Our findings thus reveal the characteristic low-energy features of PbCuTe_{2}O_{6} which qualify this compound as a true QSL material.

Field-free spin–orbit torque-induced switching of perpendicular magnetization at room temperature in WTe2/ferromagnet heterostructures

Spin–orbit torque provides an efficient way to achieve switching of perpendicular magnetization, which is essential for designing energy-efficient spintronic devices. An in-plane antidamping torque combined with an out-of-plane antidamping torque can often deterministically switch perpendicular magnetization without an external magnetic field. Encouragingly, field-free perpendicular magnetization switching of a two-dimensional (2D) material WTe2/ferromagnet bilayer has been reported recently, but the working temperature (< 200 K) is quite below room temperature. Here, we demonstrate field-free perpendicular magnetization switching in the Pt/Co/Pt/WTe2 multilayer films at room temperature, which is mainly attributed to the out-of-plane antidamping torque originating from the WTe2 layer. In addition, current-induced perpendicular magnetization switching at zero magnetic field is also accomplished in the [Co/Pt]2/WTe2 multilayer film with a very large perpendicular magnetic anisotropic field (∼13 600 Oe), which is very useful for practical applications. This work offers a potential way to develop spintronic devices based on 2D materials at room temperature.

Wave nature of Rosensweig instability

The explicit analytical solution of Rosensweig instability spikes’ shapes obtained by Navier–Stokes (NS) equation in diverse magnetic field H vertical to the flat free surface of ferrofluids are systematically studied experimentally and theoretically. After carefully analyzing and solving the NS equation in elliptic form, the force balanced surface equations of spikes in Rosensweig instability are expressed as cosine wave in perturbated magnetic field and hyperbolic tangent in large magnetic field, whose results both reveal the wave-like nature of Rosensweig instability. The results of hyperbolic tangent form are perfectly fitted to the experimental results in this paper, which indicates that the analytical solution is basically correct. Using the forementioned theoretical results, the total energy of the spike distribution pattern is calculated. By analyzing the energy components under different magnetic field intensities H, the hexagon–square transition of Rosensweig instability is systematically discussed and explained in an explicit way.

Observation of Magnon Spin Transport in BiFeO3 Thin Films

AbstractMagnon, a quanta of spin waves, can transport in magnetically ordered insulators without substantial heat dissipation. The recently demonstrated magnon‐mediated spin torque through antiferromagnetic insulators is regarded as a highly efficient approach for electrical manipulation of magnetization. To control the magnon transport in antiferromagnets, a very large magnetic field is required, since antiferromagnets show immunity to external magnetic disturbance. The antiferromagnetic order can be electrically controlled in multiferroic materials via the magnetoelectric coupling between the antiferromagnetic and ferroelectric orders. Here, we report the experimental observation of magnon spin transport through multiferroic BiFeO3 thin films in SrRuO3/BiFeO3/NiFe tri‐layers at room temperature. We find highly efficient magnon current transmission through BiFeO3 thin film with a thickness exceeding 80 nm by the spin pumping measurement. The magnon spin‐torque efficiency in the tri‐layers measured by the spin‐torque ferromagnetic resonance is comparable with that in the SrRuO3/NiFe bilayer. This results suggest multiferroic BiFeO3 to be an excellent platform for investigating the antiferromagnetic magnon transport and developing magnonic devices.

Suppressing the false magnetic field in beam-splitting Faraday rotation measurement.

In laser-plasma experiments, the beam-splitting Faraday rotation measurement is usually used for mapping the magnetic field. Due to the geometric characteristics of the beam-splitting configuration, the split beams are not always incident normally on the image plane, and their spots have different shapes and intensity distributions. Ignoring these issues will inevitably introduce errors in polarization calculation and then generate large false magnetic fields. We introduced the restoration method to recover the spots and suppress the false magnetic field. We applied this method to ZEMAX simulation data and Shenguang-II experimental data. Compared to the method of directly overlaying the spots, it can reduce the average false magnetic field by about 50%. And the false magnetic field at the edge of the spot is reduced by one order of magnitude. We can highly improve the accuracy of the magnetic field measurement with the Faraday rotation method.

Large effective magnetic fields from chiral phonons in rare-earth halides.

Time-reversal symmetry (TRS) is pivotal for materials' optical, magnetic, topological, and transport properties. Chiral phonons, characterized by atoms rotating unidirectionally around their equilibrium positions, generate dynamic lattice structures that break TRS. Here, we report that coherent chiral phonons, driven by circularly polarized terahertz light pulses, polarize the paramagnetic spins in cerium fluoride in a manner similar to that of a quasi-static magnetic field on the order of 1 tesla. Through time-resolved Faraday rotation and Kerr ellipticity, we found that the transient magnetization is only excited by pulses resonant with phonons, proportional to the angular momentum of the phonons, and growing with magnetic susceptibility at cryogenic temperatures. The observation quantitatively agrees with our spin-phonon coupling model and may enable new routes to investigating ultrafast magnetism, energy-efficient spintronics, and nonequilibrium phases of matter with broken TRS.

Effects of electron–phonon coupling and Rashba spin–orbit interaction on thermodynamic and magnetic properties of quantum dots

The thermodynamic and magnetic properties of quantum-dot structures subjected to an applied magnetic field were studied, including the longitudinal optical–phonon interaction and the Rashba spin–orbit effect. The Schrödinger equation was solved to determine the energy levels. The partition function was evaluated by summing the accessible energy levels and was then utilized to calculate the thermomagnetic functions. In this paper, we present magnetic properties by considering three interacting polarons. Our results indicated that at B=0T, the susceptibility exhibits diamagnetic behavior for all values of the Rashba spin–orbit parameter. However, the magnetic susceptibility increases with an applied magnetic field, and the system exhibits paramagnetic behavior under moderate magnetic fields. However, in situations with and without the polaron effect, the susceptibility is saturated at 0(meV/T2) under large magnetic fields. In this study, we showed that the Rashba spin–orbit interaction (SOI) strengthens the cutoff magnetic field Bc (the B value at which the magnetic nature of the dot changes from diamagnetic to paramagnetic). Rashba SOIs reduce the mean energy of the system, including polaronic interactions. Under the polaron effect, the heat capacity curve shifts to lower temperatures. A quantitative description of the magnetocaloric effect (ΔS) as a function of the Wigner and Rashba spin–orbit parameters is presented.

Magnetic haptic device using miniature SmFeN powder magnets in PCB-on-MEMS system

This paper reports a magnetic microactuator for haptic applications. The actuator consists of a Si chip and two printed circuit boards (PCBs), and the total size of the device is 7.8 mm × 7.8 mm × 2.4 mm. A tiny magnet is embedded into the Si chip and actuated by a current flowing in the PCBs. The mechanical and electrical parts are separated on the Si chip and the PCBs, respectively, and there is no electrical connection between them, allowing simple fabrication and assembly. The magnet, made from a mixture of SmFeN magnetic powder and wax, exhibits a large magnetic field of 0.4 T. The magnet is supported by soft springs of parylene, enabling a large displacement amplitude, a low resonance frequency, and high mechanical robustness. The measured resonance frequency and amplitude are 139 Hz and 62 µm, respectively. The rise and fall times of the vibration of the device at 100 mA drive are 19 ms and 52 ms, respectively. Sensory analysis revealed that the haptic device created the haptic sensation on a scale of three, weak, medium, and strong intensity, with input currents from 50 mA to 200 mA.

Active correction of window Faraday effects for ITER laser diagnostics

Measurement of the change in polarization of a laser beam traversing a magnetized plasma is a standard diagnostic technique for extracting key plasma parameters, including density and current profile. Depending on the polarization orientation of the incident laser beam relative to theplasma magnetic field, the polarization change is denoted as either Faraday rotation or Cotton-Mouton effect. On ITER three laser diagnostics will make use of this effect to make their measurements. Unfortunately, this effect is also evident when the laser beam passes through the vacuum window. The large magnetic field and finite verdet constant of the window material mean that on ITER this effect — in particular faraday rotation — is non-negligible, and needs to be disentangled from the desired measurement parameter. The Toroidal Interferometer-Polarimeter (TIP) and Density Interferometer-Polarimeter (DIP), in particular, are affected. Both diagnostics use lasers in the 5–10 μm range, and will use zinc-selenide (ZnSe) as the vacuum window material. In order to compensate for the unwanted window distortion a sensor is being developed to monitor the magnetic field perpendicular to the window and activelycorrectfor the faraday rotation in real time. The sensor consists of an inductive coil closely fitted just in front of the window disc. It comprises several turns of fine wire in center-tap configuration. Both the raw voltage signal, as well as the integrated signal, will be monitored to estimate the magnetic field through the window disk. The system is designed to measure fields up to B <1 T with an accuracy of 0.01 T, at frequencies of D.C. to 1 kHz. The backend electronics will leverage off similar technology developed for other ITER magnetics systems. Using the real-time magnetic field information, in conjunction with published and/or measured data on the verdet constant of the ZnSe window material, in-house developed software will estimate the faraday rotation induced by passing through the window.An initial prototype of the sensor has been fabricated and results from preliminary characterization trials of the system are presented. Detailed testing is planned for the future using the DIP system prototype currently under development.

Fluctuation of Magnetic Field in Magnetic Nano-Particles Thermometer

In this study, some important factors have been identified for the fluctuation of the magnetic field over time, which provides a basis for improving the temperature measurement accuracy and long-term stability of the magnetic nanoparticles thermometer (MNPT). We improved the mathematical model between the relative error of the magnetic induction intensity and the temperature measurement error of MNPT. The simulation founded that when the relative error of the magnetic induction intensity is kept within the range of &lt;0.01%, the temperature measurement error is less than 0.1 K. Then, the multi-physics (magnetic field, temperature field, and thermal stress field) coupling relationship in the Helmholtz coil is established. During the coupling process, the temperature field of the Helmholtz coil affects the resistance of coil wire, and its thermal stress field is affected by the temperature field, which also changes the coil radius. After the temperature field and thermal stress field change, the magnetic field fluctuates immediately. Further simulation found that the problem of coil temperature rise becomes more serious as the size of the Helmholtz coil increases. The method of forced air cooling can make the fluctuation of the large Helmholtz coil magnetic field &lt; 0.01%, and improve the measurement accuracy of MNPT.

Magnetic Putty as a Reconfigurable, Recyclable, and Accessible Soft Robotic Material.

Magnetically hard materials are widely used to build soft magnetic robots, providing large magnetic force/torque and macrodomain programmability. However, their high magnetic coercivity often presents practical challenges when attempting to reconfigure magnetization patterns, requiring a large magnetic field or heating. In this study, magnetic putty is introduced as a magnetically hard and soft material with large remanence and low coercivity. It is shown that the magnetization of magnetic putty can be easily reoriented with maximum magnitude using an external field that is only one-tenth of its coercivity. Additionally, magnetic putty is a malleable, autonomous self-healing material that can be recycled and repurposed. The authors anticipate magnetic putty could provide a versatile and accessible tool for various magnetic robotics applications for fast prototyping and explorations for research and educational purposes.

Stray magnetic fields from elliptical-shaped and stadium-shaped ferromagnets

An artificial spin ice consisting of numerous ferromagnets has attracted attention because of its applicability to practical devices. The ferromagnets interact through their stray magnetic field and show various functionality. The ferromagnetic element in the spin ice was recently made in elliptical-shape or stadium-shape. The former has a narrow edge, expecting to generate a large stray magnetic field. The latter has a large volume and is also expected to generate a large stray magnetic field. Here, we estimate the stray magnetic field by numerically integrating the solution of the Poisson equation. When magnetization is parallel to an easy axis, the elliptical-shaped ferromagnet generates a larger stray magnetic field than the stadium-shaped ferromagnet. The stray magnetic fields from both ferromagnets for arbitrary magnetization directions are also investigated.

Survival of fossil fields during the pre-main sequence evolution of intermediate-mass stars

Context. Chemically peculiar Ap and Bp stars host strong large-scale magnetic fields in the range of 200 G up to 30 kG, which are often considered to be the origin of fossil magnetic fields. Aims. We assess the evolution of such fossil fields during the star formation process and the pre-main sequence evolution of intermediate stars based on: fully convective models, models including a transition to a radiative protostar, and models with a radiative core. We also examine the implications of the interaction between the fossil field and the core dynamo. Methods. We employed analytic and semi-analytic calculations, combined with current observational constraints. Results. For fully convective models, we show that magnetic field decay via convection can be expected to be very efficient for realistic parameters of turbulent resistivities. Based on the observed magnetic field strength-density relation, as well as the expected amount of flux loss due to ambipolar diffusion, it appears unlikely that convection could be suppressed via strong enough magnetic fields. On the other hand, a transition from a convective to a radiative core could very naturally explain the survival of a significant amount of flux, along with the presence of a critical mass. We show that in some cases, the interaction of a fossil field with a core dynamo may further lead to changes in the surface magnetic field structure. Conclusions. In the future, it will be important to understand in more detail how the accretion rate evolves as a function of time during the formation of intermediate-mass protostars, including its impact on the protostellar structure. The latter may even allow us to derive quantitative predictions concerning the expected population of large scale magnetic fields in radiative stars.