Magnetic Devices Research Articles

Solving combinatorial optimization problems through stochastic Landau-Lifshitz-Gilbert dynamical systems

We present a method to approximately solve general instances of combinatorial optimization problems using the physical dynamics of three-dimensional (3D) rotors obeying Landau-Lifshitz-Gilbert dynamics. Conventional techniques to solve discrete optimization problems that use simple continuous relaxation of the objective function followed by gradient-descent minimization are inherently unable to avoid local optima, thus producing poor-quality solutions. Our method considers the physical dynamics of macrospins capable of escaping from local minima, thus facilitating the discovery of high-quality, nearly optimal solutions, as supported by extensive numerical simulations on a prototypical quadratic unconstrained binary optimization (QUBO) problem. Our method produces solutions that compare favorably with those obtained using state-of-the-art minimization algorithms (such as simulated annealing) while offering the advantage of being physically realizable by means of arrays of stochastic magnetic tunnel-junction devices. Published by the American Physical Society 2025

Biaxial Magnetic Anisotropy for Multimodal Ferromagnetic Resonance Through Two‐Dimensional Permalloy Microstructure Array

The ferromagnetic resonance (FMR) properties of ferromagnetic films play an important role in microwave magnetic devices. Currently, micropatterning of ferromagnetic films is utilized to arbitrarily design the FMR performance, with one‐dimensional control being primarily considered. This work develops a two‐dimensional permalloy microstructure array as a controllable design for biaxial magnetic anisotropy and multimodal FMR tuning. Under a magnetic field with a fixed angle, the microstructure containing stripe domains generates both a high‐frequency optical branch (4.1 GHz) and a low‐frequency acoustic branch (2.28 GHz) simultaneously. By adjusting the width of the microstrips that compose the permalloy microgrid array, both the frequency and the transition field of the acoustic and optical branches can be tuned. Furthermore, selective control of the desired resonance mode is achieved by changing the microstrip width in a single direction. This controllable design, featuring coexisting acoustic and optical branches, provides a new approach for the development of multichannel electromagnetic shielding and high‐frequency magnetic devices.

Monte Carlo Investigation of the Critical Behavior of a Core–Shell Nanotube

Monte Carlo simulation is employed to examine a ferrimagnetic Ising‐type hexagonal nanotube, featuring a spin‐ core embedded in a spin‐1 shell. The impacts of specific exchange interactions and the crystal field on the magnetization and phase diagrams of the system are analyzed and discussed. Under certain physical conditions, the nanotube exhibits first‐ and second‐order phase transitions and compensation temperatures. The characteristics highlighted are significant for the technological applications of these systems, such as magnetic storage devices, sensors, and drug delivery systems.

Physical properties of ultrasonic assisted MWCNT/Ni0.5Co0.5Pr0.2Fe1.8O4 nanocomposites for future energy storage applications

The demand for materials with superior magnetic and dielectric properties is critical for the advancement of high-performance electronic and magnetic devices. In response to this need, Ni0.5Co0.5Pr0.2Fe1.8O4 (NiCoPrFeO) nanoparticles were synthesized using the sol–gel auto-combustion technique, known for its simplicity and versatility. To enhance the functional properties of these nanoparticles, multiwalled carbon nanotubes (MWCNTs) were incorporated, recognized for their high electrical conductivity and low density, to create a novel nanocomposite. The structural and physical properties of the prepared NiCoPrFeO/MWCNTs nanocomposites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), and Impedance Analysis. XRD confirmed the successful formation of the nanocomposite NiCoPrFeO/MWCNTs. TEM provided detailed insights into particle size to be around 18.553 and the interactions between the nanoparticles and MWCNTs. FTIR spectra indicated the presence of absorption bands ‘ν1′ and ‘ν2′ to be around 545 and 415 cm−1 which is characteristic of the cubic spinel structure. The addition of MWCNTs significantly improved the magnetic properties of the nanocomposite, with higher MWCNT concentrations leading to stronger magnetization, as shown by VSM analysis the values of Mr, Ms and Hc were found between 1.41 to 4.79 emu/g, 16.67 to 24.35 emu/g and 204.29 to 569.77 Oe, respectively. The dielectric properties, including dielectric constant, dielectric loss, loss tangent, and AC conductivity, exhibited notable improvements with increasing MWCNT content across varying frequencies. These results suggest that NiCoPrFeO/MWCNTs nanocomposites could be a promising solution for improving materials used in electronic and magnetic devices, leading to more efficient and advanced technologies.

Design and optimization of liquid helium-free cooling systems for magnetic resonance imaging device using multi-physical modeling

Design and optimization of liquid helium-free cooling systems for magnetic resonance imaging device using multi-physical modeling

Magnetic Field-Accelerated Nonthermal Plasma Digestion for Field Pretreatment and Determination of Heavy Metals in Biological Samples.

Field analysis of heavy metals in biological samples is essential for assessing their potential threats to human health. The development of portable pretreatment and detection devices is crucial to address this challenge. Herein, a magnetic field-accelerated nonthermal plasma digestion device using dielectric barrier discharge (DBD) is designed for the rapid and environmentally friendly pretreatment of biological samples and subsequently combined with point discharge-optical emission spectrometry (PD-OES) for sensitive determination of heavy metals. With the assistance of a magnetic field, the DBD plasma digestion of a batch of six samples using a H2O + H2O2 + HNO3 system can be completed within 25-40 min, achieving the digestion efficiencies of 92-99%. The application of magnetic field enhances the electron density, excitation temperature, discharge current, and power of the DBD plasma, thereby reducing the digestion time by 40-69%. The determination of heavy metals in the digestion solution is directly performed using a miniature injection-detector based on hydride generation-PD-OES. Under the optimized conditions, the detection limits for Pb, Sb, Sn, and Bi are 2.4-8.2 μg L-1 (0.048-0.16 mg kg-1), with precisions of <5%. The accuracy and practicability of the present device are verified by measuring several certified reference materials, including GBW10023 (laver) and GBW10044 (rice), and real rice, laver, fish, milk, and blood samples. With its advantages of environmental sustainability, short digestion time, compact size, and lightweight design, the present device provides a simple and efficient tool for field analysis of toxic elements in biological samples.

Lattice thermal conductivity in CrSBr: the effects of interlayer interaction, magnetic ordering and external strain

With the continuous development of digital information and big data technologies, the ambient temperature and heat generation during the operation of magnetic storage devices play an increasingly crucial role in ensuring data security and device stability. In this study, we conducted a thorough investigation on in-plane lattice thermal conductivity of the van der Waals (vdWs) magnetic semiconductor CrSBr from bulk to monolayer using first-principles calculations and phonon Boltzmann transport equation. Our findings indicated that CrSBr show strong anisotropic thermal transport behaviors and layer number and magnetic ordering dependent lattice thermal conductivity. The lowest thermal conductivity is observed in y direction of antiferromagnetic CrSBr bilayer at all temperatures. Through the analysis of phonon spectra, phonon lifetime, heat capacity, scattering probability, phonon-phonon interaction strength, we demonstrated that out of plane acoustic phonon modes soften, the shift of Cr-Br antisymmetrical stretching vibrations, and large phonon band gap are the main factors. These results offer a comprehensive insight into phonon transport phenomena in vdWs magnetic materials.

Global and Local Shielding/Deshielding Variation in C60 and C70 Fullerenes Upon Reduction: Evaluation of Aromaticity, 13C-NMR and Anisotropy Patterns.

Fullerenes are statically pleasant species featuring symmetric cages, which can be modified upon reduction. Here, we theoretically account for the variation of 13C-NMR patterns in C60 and C70 upon six-fold reduction and the overall variation of the enabled shielding/deshielding regions induced by π and σ electrons according to different orientations of the external field and the related anisotropy. Our results show a significant modification of the chemical shift given by the main variation of the σ33 (or δ33) shielding component under the principal axis system (PAS) of the chemical shift anisotropy (CSA) at the representative carbon nucleus. For C606- a shielding cone property is enabled from any orientation, accounting for a significant spherical aromatic character. In contrast, in C706‑, a shielding cone is reserved only for an axial-oriented field, with a deshielding cone behavior obtained from the complementary equatorial orientations. The overall anisotropy shows an inner isotropic region for C60 and C606-, with a continuous anisotropic outer contour for the latter. In contrast, C70 and C706- both show larger anisotropies, given the lesser spherical shape in addition to the modified π-surface. Such information is useful for further rationalizing the implementation of magnetic anisotropic molecular devices into fullerene-based materials.

Optically Readable Multilevel Magnetic Memory States in Perpendicularly Exchange-Biased Ferromagnetic Multilayers.

The construction of multilevel magnetic states using materials with perpendicular magnetic anisotropy (PMA) offers a novel approach to enhancing the storage density and read/write efficiency of nonvolatile magnetic memory devices. In this study, optically readable multilevel magnetic domain states are achieved by inducing asymmetric interlayer interactions and decoupling the magnetic reversal behavior of individual ferromagnetic (FM) layers in exchange-biased FM multilayers with PMA. Hepta-level magnetic domain states are formed in [Co/Pt]n FM multilayers grown on an antiferromagnetic Fe2O3 layer within a relatively low magnetic field range of ∼±400Oe. Raising and lowering operations between states are demonstrated to be achievable, enabling the writing of new information without the need for initialization in multilevel magnetic memory applications. This design concept, leveraging multilevel magnetic domain states and facilitating noncontact optical reading of stored information, demonstrates the potential to enhance the storage density of nonvolatile magnetic memory devices as it eliminates the need for electrical circuits typically required in other resistive memory technologies.

Electrochemical Fabrication of Ni–Co Alloy over a Wide pH Range Using Sodium Citrate as a Complexing Agent

In this study, nickel–cobalt (Ni–Co) coatings were fabricated via electrodeposition using a 22 central composite factorial design with two central and two axial points, totaling ten experiments. The effects of pH and current density on the coatings’ chemical composition and properties were evaluated. Coatings were characterized by microstructure, morphology, magnetic properties, and corrosion resistance. The results showed that pH significantly influenced chemical composition, while current density had no notable effect. Acidic pH produced cobalt-rich coatings (43–81 at.%), with uniform morphology, higher saturation magnetization, and lower corrosion resistance. Maximum cobalt content (81 at.%) resulted in a mixed face-centered cubic (fcc) + hexagonal close-packed (hcp) phase. Alkaline pH yielded nickel-rich coatings (89–95 at.%), featuring nodular morphology, lower magnetization, higher corrosion resistance, and, exclusively, the fcc phase. The highest polarization resistance (66.1 kΩ) occurred at pH 8.83 and 60 mA/cm2, while resistance decreased with increasing cobalt content. The pH effect on deposition was linked to the formation of citrate complexes: ammonia and citrate complexes promoted nickel deposition under alkaline conditions, while stable cobalt complexes dominated in an acidic pH. These findings highlight the potential to tailor Ni–Co coatings for applications such as corrosion-resistant coatings (nickel-rich) or magnetic devices (cobalt-rich).

SOFCs integrated with SMES under dynamic power control using Chernobyl disaster optimizer

The current study uses the Chernobyl disaster optimizer (CDO), a new metaheuristic optimizer, to identify the seven unknown parameters of solid oxide fuel cells (SOFCs). The procedures of the CDO is based on physical behavior of the elaborated radiations from the well-known Chernobyl disaster according to their mass, speed, frequency, and degree of ionization. The sum of square errors (SMSE) among the estimated and the real measured output voltage datasets of SOFCs is minimized employing the CDO. Set of boundaries of the SOFC’s process is taken into consideration with the problem formulation. SOFCs stack’s model is examined at 800οC and 900οC and its performance is confirmed. The CDO extracts more precise SOFCs’ parameters compared to other competitors. The CDO’s convergence patterns and the SOFCs unit’s performance are studied and proved at steady-state by comparing its results to a number of recognized algorithms under varied operating scenarios. A significant SMSE’s values of 3.46 µV2 and 7.38 µV2 are attained at 800οC and 900οC, respectively by the CDO. As a result, the polarization principal curves of the measured and estimated voltage datasets are checked and verified with very close matching. The dynamic behavior of the SOFCs stack is examined in relation to direct load, electric networks, and superconducting magnetic energy storage devices (SMES) for additional validation and illustration. The role of the SOFCs stack in controlling the active and reactive power delivered to the network and direct load is investigated using two controllers: one to control the inverter, which converts the SOFC’s dc output to the main network, and the other to control the SMES. The Simulink/MATLAB environment is used to indicate the validity of the proposed framework under both steady-state and dynamical conditions. The comprehensive assessments show that the CDO capabilities are very effective when used with microgrids.

Noncollinear Magnetic Configurations in Frustrated Magnets.

The exploration of materials with nanoscale noncollinear configurations has been continuously attracting attention due to the prospective applications in high-performance magnetic devices. Compared to ferromagnetic materials, noncollinear structures in frustrated magnets hold greater research value due to their smaller sizes and unique properties. However, an effective description of the nanoscale noncollinear domain structures in frustrated magnets is lacking. Here, we propose an approach based on a phase-field model to predict magnetic configurations in frustrated magnets within a square lattice system. The metastable domain structures have been determined under the competition between the nearest-neighbor ferromagnetic interaction and the third-neighbor antiferromagnetic exchange interaction. The conditions required for the stable existence of noncollinear phases have been theoretically derived. Additionally, we investigate the spin response to external fields for different J1 - J3 values, and we also examine the spin response to external fields for various values of J1 - J3, focusing on the emerging topological soliton states. Our research results not only hold crucial significance in facilitating an understanding of the complex characteristics of frustrated magnets but also offer theoretical guidance for further exploring the application potentials of these systems in diverse aspects such as emerging inductor devices and storage devices.

Simulation of ion cyclotron range of frequencies heating in the proton–boron plasma of the spherical tokamak

Abstract Ion cyclotron range of frequencies (ICRF) heating is crucial in magnetic confinement fusion devices that utilize proton–boron11 (p11B) as an advanced fuel, as it requires higher ion temperatures for their reactions. This work investigates the ICRF heating characteristics of hydrogen (H) ions at the second harmonic frequency and 11B ions at the fundamental frequency in a p11B plasma within a spherical tokamak. It is found that H ions second harmonic is better than 11B ions fundamental for ion power absorption. We simulate the ICRF heating effects of the 11B fraction in plasma and the wave vector parallel to the magnetic field ( k ‖ ) of the antenna using full-wave codes and the kinetic dispersion relation solver. In second harmonic heating of H ions, the power deposition primarily occurs on the H ions themselves, and, the total power absorption will exceed 50%, up to 58%, when X[11B] &gt; 6%. Heating the electrons is easier in the fundamental frequency heating of 11B ions scenario.

In-plane magnon valve effect in magnetic insulator–heavy metal–magnetic insulator device

In-plane magnon valve effect in magnetic insulator–heavy metal–magnetic insulator device

Feasibility and Challenges of Pyeloureteral Magnetic Anastomosis Device in Domestic Pigs: A Stepwise Approach with Extended Observation.

The pyeloureteral anastomosis remains the most challenging part of pyeloplasty. A purpose-built anastomotic device could simplify this step and potentially improve outcomes. The concept of a pyeloureteral magnetic anastomosis device (PUMA) was proven in minipigs, but only in short term. Our aim was to test the PUMA in domestic pigs and achieve a prolonged follow-up period. Five female domestic pigs underwent laparoscopy and ligation of the left ureter. Four weeks later, laparoscopic implantation of the PUMA was planned. Removal of the device and a retrograde contrast study were scheduled after another 4 weeks. The experiment was terminated when the animals could no longer be properly cared for due to their weight. Due to unexpected smaller ureteric diameters, a modified PUMA could only be successfully inserted in pig number 3 (49 kg). Four weeks later, the device was found to be dislocated, but the anastomosis remained patent. After modifying the study protocol, the PUMA was successfully implanted in pigs number 4 (96 kg) and 5 (68 kg) 8 weeks after ureteric ligation. Pig 4 developed malignant hyperthermia and died. In pig 5, the magnets were removed 4 weeks later. After an additional 8 weeks, the animal reached 135 kg and was terminated. The anastomosis remained patent and preserved its diameter. Despite limitations, our study successfully demonstrated that the PUMA can achieve a patent ureteric anastomosis in domestic pigs. This suggests a potential for minimally invasive ureteric anastomosis in clinical settings. Further research is needed to optimize the technique and validate its effectiveness in humans.

Charge doping into spin minority states mediates doubling of TC in ferromagnetic CrGeTe3

The recent discovery of the persistence of long-range magnetic order when van der Waals magnets are thinned towards monolayers provides a tunable platform for engineering of novel magnetic structures and devices. Here, we study the evolution of the electronic structure of CrGeTe3 as a function of surface electron doping. From angle-resolved photoemission, we observe spectroscopic fingerprints that this electron doping drives a marked increase in TC, reaching values more than double that of the undoped material, in agreement with recent studies using electrostatic gating. Together with density functional theory calculations and Monte Carlo simulations, we show that, surprisingly, the increased TC is mediated by the population of spin-minority Cr t2g states, forming a half-metallic 2D electron gas. This promotes a novel variant of double exchange, and unlocks a significant influence of Ge – which was previously thought to be electronically inert in this system – in mediating Cr-Cr exchange.

Observation of Large Low-Field Magnetoresistance in Layered (NdNiO3)n:NdO Films at High Temperatures.

Large low-field magnetoresistance (LFMR, <1 T), related to the spin-disorder scattering or spin-polarized tunneling at boundaries of polycrystalline manganates, holds considerable promise for the development of low-power and ultrafast magnetic devices. However, achieving significant LFMRtypically necessitates extremely low temperatures due to diminishing spin polarization as temperature rises. To address this challenge, one strategy involves incorporating Ruddlesden-Popper structures (ABO3)n:AO, which are layered derivatives of perovskite structure capable of potentially inducing heightened magnetic fluctuations at higher temperatures. Here, a remarkable LFMR of up to 1.0×103% is obtained in the layered (NdNiO3)n:NdO films with a high and wide temperature range (190-240 K). This finding underlines that the layered (NdNiO3)n:NdO (n = 1) structure show a complex magnetic structure above TMI of perovskite NdNiO3, where small ferromagnetic domains are embedded in the antiferromagnetic domains, raising the tunneling barriers and magnetic fluctuations at high temperatures. Furthermore, applying a low magnetic field (<0.1 T) near TMI effectively mitigates the disruption of antiferromagnetic order structures at boundaries, then a higher temperature is required to break the inhibition of ferromagnetic to antiferromagnetic phase transition. The results contribute significantly to the advancement of magnetic devices capable of achieving substantial LFMR at room temperature.

Bias Calibration of Optically Pumped Magnetometers Based on Variable Sensitivity.

Optically pumped magnetometers (OPMs) functioning in the spin-exchange relaxation-free (SERF) regime have emerged as attractive options for measuring weak magnetic fields, owing to their portability and remarkable sensitivity. The operation of SERF-OPM critically relies on the ambient magnetic field; thus, a magnetic field compensation device is commonly employed to mitigate the ambient magnetic field to near zero. Nonetheless, the bias of the OPM may influence the compensation impact, a subject that remains unexamined. This paper introduced an innovative bias calibration technique for OPMs. The sensitivity of the OPM was altered by adjusting the cell temperature. The output of the OPM was then documented with varying sensitivity. It is assumed that the signal exhibits a linear correlation with the environmental magnetic field, and the statistical characteristics of the magnetic field are identical for both measurements, upon which the bias of the OPM is assessed. The bias was subsequently considered in the feedback magnetic field compensation mechanism. The results indicate that this technique might successfully reduce environmental magnetic fluctuations and enhance the sensitivity of the OPM. This technique measured the magnetic field produced by the human heart, confirming the viability of the ultra-weak biomagnetic field measurement approach.

Controllable z-Polarized Spin Current in Artificially Structured Ferromagnetic Oxide with Strong Spin-Orbit Coupling.

Realizing field-free switching of perpendicular magnetization by spin-orbit torques is crucial for developing advanced magnetic memory and logic devices. However, existing methods often involve complex designs or hybrid approaches, which complicate fabrication and affect device stability and scalability. Here, we propose a novel approach using z-polarized spin currents for deterministic switching of perpendicular magnetization through interfacial engineering. We fabricate La0.67Sr0.33MnO3-SrIrO3 (LSIMO) thin films with robust spin-orbit coupling and ferromagnetic order through orbital and lattice reconstruction, integrating SrIrO3 and La0.67Sr0.33MnO3 materials. Our investigation reveals that y- and z-polarized spin currents, driven by the spin Hall and spin-orbit precession effects, enable field-free switching of perpendicular magnetization. Notably, the z-polarized spin currents are tunable via the in-plane magnetization of LSIMO. These findings present a promising pathway for the development of energy-efficient spintronic devices, offering improved performance and scalability.

Nanoimprint lithography-assisted block copolymer self-assembly for hyperfine fabrication of magnetic patterns based on L10-FePt nanoparticles

Abstract L10-FePt-type bit-patterned media has provided a promising alternative for ultrahigh-density magnetic recording systems in the current digital era, but rapid fabrication of magnetic patterns with hyperfine bit islands is still challenging, especially with the target for miniaturization and scalable production simultaneously. Herein, Fe,Pt-containing block copolymers were utilized as single-source precursors for solution-processable patterning and subsequent generation of the demanding magnetic FePt dots by in situ pyrolysis. High-throughput nanoimprint lithography was initially employed to fabricate the predefined bit cells precisely, and then the intrinsic self-assembly of phase-separated block copolymers further drove the formation of accurate bit islands. Benefiting from the synergistic effect of top-down lithographic approach and bottom-up self-assembly, the customizable patterns could be achieved for large-scale mass production in targeted areas, but high-density isolated dots could also be accurately aligned along the patterned features after subsequent self-assembly. This reliable strategy would provide a good avenue to precisely construct ultrahigh-density magnetic data storage devices.