Anisotropic Magnetic Materials Research Articles

Analysis of magnetostriction of oriented silicon steel under motor magnetic field

The performance requirements of motors are gradually increasing, and anisotropic soft magnetic materials have been applied in motors to improve performance, The magnetostriction of anisotropic soft magnetic materials is one of the main contributors in extensive research on anisotropic soft magnetic material transformers. Compared to transformers, the magnetic field in motors has more complex harmonic and multi-directional characteristics. In this paper, the magnetic field of motors stator teeth under both no-load and load conditions is calculated and analyzed to research magnetostriction of anisotropic soft magnetic materials in motor magnetic field and predict the NVH performance of anisotropic soft magnetic material motors accurately. Furthermore, the magnetostriction in different magnetization angles is investigated for the multi-directional characteristics, and the result is explained from microscopic principles. This paper focuses on a splicing oriented silicon steel (OSS) motor, the magnetization angle of OSS in motor varying from 0° to 90°. Firstly, the equivalent formulas of magnetic field are obtained under the analytical and finite element calculations. After that, the frequency and direction of experiment magnetic field are confirmed and the magnetostriction of OSS in different magnetization angle and frequency is measured. In the end, the variation character of magnetostriction of OSS is summarized.

Tuning magnetoresistance of chromium chloride tunnel junction through the interface and multi-field effect

<sec>Magnetic tunnel junctions (MTJs) serve as essential platforms for investigating spin transport properties, magnetic phase transitions, and anisotropy in magnetic materials. Recently two-dimensional van der Waals antiferromagnetic insulators like chromium chloride (CrCl<sub>3</sub>) or chromium iodide (CrI<sub>3</sub>) have been used to develop spin-filtering magnetic tunnel junctions (sf-MTJs), improving the device performance for material property exploration and spintronic applications. However, it is crucial to recognize that the spin-filtering effect is not the sole determining factor of tunneling magnetoresistance (TMR) in these junctions; the interface magnetic exchange interactions and adjustable electrode density of states (DOS) fluctuations, response to applied electric or magnetic fields, can also influence the tunneling current.</sec><sec>In this study, we fabricate MTJ devices by using mechanically-exfoliated few-layer CrCl<sub>3</sub> as the tunnel barrier and few-layer graphene (FLG) as electrodes through dry transfer technique. Conducting low-temperature quantum transport measurements, we observe unconventional TMR behaviors, including bias-voltage-dependent TMR, oscillatory tunneling current under high magnetic fields, and tunable tunneling current via gate voltage.</sec><sec>A qualitative model of elastic tunneling current is employed to analyze the spin and band characteristics of the MTJ device. The observed bias-voltage-dependent TMR is attributed to the changes in the tunneling mechanism due to magnetic proximity effect, which induces magnetization in the FLG electrode near the FLG/CrCl<sub>3</sub> interface. The antiparallel alignment of polarized spin to CrCl<sub>3</sub>’s magnetization results in injected charge carriers facing a higher tunnel barrier, leading to negative TMR at lower bias voltages. As the bias voltage increases, the magnetic proximity effect lessens, and the device reverts to its conventional spin-filtering functionality. The oscillatory tunneling current is explained by the graphene electrode’s quantum oscillatory density of states behavior under vertical magnetic fields, which can be controlled by the applied gate voltage.</sec><sec>This study contributes to the understanding of previously unexplored TMR phenomena in two-dimensional MTJs, deepening our insights into carrier transport properties in these heterostructures and broadening avenues for investigating the physical properties of two-dimensional magnetic materials and their spintronic applications.</sec>

Anisotropy in magnetic materials for sensors and actuators in soft robotic systems.

The field of soft intelligent robots has rapidly developed, revealing extensive potential of these robots for real-world applications. By mimicking the dexterities of organisms, robots can handle delicate objects, access remote areas, and provide valuable feedback on their interactions with different environments. For autonomous manipulation of soft robots, which exhibit nonlinear behaviors and infinite degrees of freedom in transformation, innovative control systems integrating flexible and highly compliant sensors should be developed. Accordingly, sensor-actuator feedback systems are a key strategy for precisely controlling robotic motions. The introduction of material magnetism into soft robotics offers significant advantages in the remote manipulation of robotic operations, including touch or touchless detection of dynamically changing shapes and positions resulting from the actuations of robots. Notably, the anisotropies in the magnetic nanomaterials facilitate the perception and response with highly selective, directional, and efficient ways used for both sensors and actuators. Accordingly, this review provides a comprehensive understanding of the origins of magnetic anisotropy from both intrinsic and extrinsic factors and summarizes diverse magnetic materials with enhanced anisotropy. Recent developments in the design of flexible sensors and soft actuators based on the principle of magnetic anisotropy are outlined, specifically focusing on their applicabilities in soft robotic systems. Finally, this review addresses current challenges in the integration of sensors and actuators into soft robots and offers promising solutions that will enable the advancement of intelligent soft robots capable of efficiently executing complex tasks relevant to our daily lives.

Design and adaptive finite element simulation of conformal transformation optics devices with isotropic materials

Traditional transform optical devices are designed from anisotropic magnetic materials which are difficult to fabricate. In this paper, we design and simulate a conformal carpet invisible cloak and bending waveguide device with isotropic material. According to the existing conformal coordinate transformation, we deduce the perfect parameters required by the conformal device. And the finite element method and error analysis of the model equation and the basic process of adaptive algorithm are given. We first simulated a carpet cloak and bending waveguide device with perfect parameters; then we used the idea of parameter segmentation to design a carpet cloak that requires 35 isotropic materials and use the idea of layering to design the conformal bending waveguide device, and relevant numerical results are presented; finally, we designed the adaptive finite element algorithm to realize the numerical simulation of Maxwell's equations in isotropic material.

Model of a 3D Magnetic Permeability Tensor Considering Rotation and Saturation States in Materials with Axial Anisotropy.

The paper proposes a 3D extension of the linear tensor model of magnetic permeability for axially anisotropic materials. In the proposed model, all phases of a magnetization process are considered: linear magnetization, magnetization rotation, and magnetic saturation. The model of the magnetization rotation process is based on the analyses of both anisotropic energy and magnetostatic energy, which directly connect the proposed description with physical phenomena occurring during a magnetization process. The proposed model was validated on the base of previously presented experimental characteristics. The presented extension of the tensor description of magnetic permeability enables the modelling of inductive devices with cores made of anisotropic magnetic materials and the modelling of magnetic cores subjected to mechanical stresses. It is especially suitable for finite element modelling of the devices working in a magnetic saturation state, such as fluxgate sensors.

C-axis Oriented Polycrystalline BaFe12-xCoxO19 (x = 0, 0.3, 0.6, 0.9) for Millimeter Wave Self-biased Circulator at Ka Band

The anisotropic hexagonal magnetic material is prepared using conventional ceramic process. The high magnetic anisotropy field of hexagonal is essential to extend the device bandwidth for circulator operating at millimeter wave band. The modified hexagonal BaFe12-xCoxO19 with about 9 kOe anisotropy field and its Electromagnetic property are presented. And a simulation certificating the circulator at Ka-band is given at the end of the paper.

Spin wave excitations in a nanowire spin Hall oscillator with perpendicular magnetic anisotropy

Spin torque oscillators (STOs) are emerging microwave devices that can potentially be used in spin-logic devices and the next-generation high-speed computing architecture. Thanks to their non-linear nature, STOs are easily tunable by the magnetic field and the dc current. Spin Hall nano-oscillators are promising types of STOs and most of the current studies focus on localized modes that can be easily excited. Here, we study using micromagnetic simulations, the nature of the spin-torque-induced excitations in nanowire devices made of perpendicular magnetic anisotropy (PMA) materials. Our results showed that, upon including PMA, the excitation of localized and propagating spin wave modes is feasible. We study the nature of the mode excitations as a function of the PMA strength (Ku) and the current. Indeed, we estimate a critical value of Ku to allow for the excitation of the propagating spin wave. We attribute this mode selectivity between localized and propagating modes to the magnitude and the change of the sign of the nonlinearity of the system from negative to positive at a non-zero Ku, which is supported by analytical calculations. Our results provide deep insight into engineering microwave devices for future magnonic and computational applications.

Improved gyrator-capacitor modeling of inductive components with a FINEMET-type nanocrystalline alloy core using SPICE

• An improved gyrator-capacitor SPICE model of inductive components with the implementation of a Langevin function-based, magnetization curve model. • The application of a differential, evolution-based method of identification of model parameters for FINEMET-type nanocrystalline alloys. • The high accuracy of the improved gyrator-capacitor SPICE model creates new possibilities for the development and optimization of power conversion devices. Power conversion devices, such as switching mode power supplies, require the use of a wide range of inductive components. Despite the intense development of advanced magnetic materials for the cores of such elements, SPICE models of these components are still inaccurate and oversimplified. In this paper, a SPICE model of inductive components is used to show that an improved gyrator-capacitor can be produced using cores made of both isotropic and anisotropic soft and magnetic materials - particularly nanocrystalline alloys. The implementation of a Langevin, function-based, magnetization curve model, as well as the application of a differential, evolution-based method of identification of model parameters, allowed for the effective modeling of inductive cores that were made from FINEMET-type nanocrystalline alloys. The modeling quality was quantitatively confirmed by measuring the R-squared coefficient, which exceeds 0.97 for driving frequencies up to 100 kHz. The high accuracy of the improved gyrator-capacitor SPICE model creates new possibilities for the development and optimization of power conversion devices.

Ultrafast laser-induced control of magnetic anisotropy in nanostructures

Employing short laser pulses with a duration below 100 fs for changing magnetic state of magnetically-ordered media has developed into a distinct branch of magnetism femtomagnetism which aims at controlling magnetization at ultimately short timescales. Among plethora of femtomagnetic phenomena, there is a class related to impact of femtosecond pulses on magnetic anisotropy of materials and nanostructures which defines orientation of magnetization, magnetic resonance frequencies and spin waves propagation. We present a review of main experimental results obtained in this field. We consider basic mechanisms responsible for a laser-induced change of various anisotropy types: magnetocrystalline, magnetoelastic, interfacial, shape anisotropy, and discuss specifics of these processes in magnetic metals and dielectrics. We consider several examples and describe features of magnetic anisotropy changes resulting from ultrafast laser-induced heating, impact of laser-induced dynamic and quasistatic strains and resonant excitation of electronic states. We also discuss perspectives of employing various mechanisms of laser-induced magnetic anisotropy change for enabling processes prospective for developing devices. We consider precessional magnetization switching for opto-magnetic information recording, generation of high-frequency strongly localized magnetic excitations and fields for magnetic nanotomography and hybrid magnonics, as well as controlling spin waves propagation for optically-reconfigurable magnonics. We further discuss opportunities which open up in studies of ultrafast magnetic anisotropy changes because of using short laser pulses in infrared and terahertz ranges. Keywords: magnetic anisotropy, femtosecond laser pulses, femtomagnetism, picosecond acoustics, magnetization precession, spin waves, magnetization switching, magnon-phonon coupling.

Spin–orbit torque driven perpendicular magnetization switching in Re/CoFeB/MgO with high thermal stability

Writing using spin–orbit torque (SOT) has been widely investigated in the field of magnetic random-access memory (MRAM). Heavy metal (HM)/CoFeB/MgO is the core of this SOT-MRAM structure. The heterostructure consisting of Ta as the spin current source and CoFeB/MgO as the perpendicular magnetic anisotropy (PMA) material is the most researched structure, owing to its high tunneling magnetoresistance ratio. However, Ta is difficult to integrate into the CMOS process due to its poor thermal stability against annealing at temperatures greater than 350 °C. Currently, β-tungsten (W) is the only HM with the CoFeB/MgO system, which can provide both thermal stability and SOT switching. Nevertheless, to achieve the high resistive β phase of W is a challenging task. Here, we report another material rhenium (Re) capable of providing thermally stable PMA up to temperature 425 °C with a perpendicular anisotropic field greater than 5000 Oe; Re possesses a spin hall angle (ϴSH) of 0.065 ± 0.003, and SOT switching can be achieved with a current density around 1.36 × 1011 A/m2. Our findings pave a new avenue for the material design of perpendicular SOT-based MRAM.

4D printing of patterned multimaterial magnetic hydrogel actuators

This paper demonstrates a new class of printable magnetic hydrogels that can be successfully used for multimaterial direct ink printing (4D printing) of soft actuators. To date, most reports on magnetic actuation have not considered biocompatibility issues associated with magnetic materials and synthetic polymers. For this reason, in this study, considerable attention was given to developing bionanocomposites that exhibit noncytotoxicity and biocompatibility and hence may be used in biomedical applications. Three inks with various concentrations of magnetic nanoparticles (MNPs) were used to print 3D objects, such as tubes (wheels), cubes, and cantilevers. The interactions between MNPs and hydrogel precursor network accounted for excellent shear thinning properties of the inks. Usually, hydrogel actuators move or change a shape upon anisotropic swelling and deswelling, possible only in an aqueous environment. Our study addresses this challenge by incorporating magnetic nanoparticles into the hydrogel, allowing for contactless in-air control of hydrogel motion. Because of the high structural integrity of the hydrogel, we can state that multimaterial direct ink printing is an excellent method for obtaining a 3D construct of high resolution, shape fidelity, tunable distribution of MNPs, and induced macroscopic anisotropy. The magnetic hydrogels are not only highly porous and noncytotoxic towards fibroblasts but also exhibit good mechanical stability and unique magnetic responsiveness. The simple approach allowed us to fabricate different magnetic actuators with various patterns, composed of magnetic and non-magnetic materials. The results demonstrate the interplay between magnetic and nonmagnetic hydrogels that influences the actuation performance of multimaterial objects, as illustrated by magnetically induced rolling, jumping, and bending. It was shown that programmable patterning of the hydrogels leads to the development of macroscopically anisotropic magnetic material. Our study confirmed that the intersection of 4D printing of magnetically responsive hydrogel materials and programmable patterning promises to fulfill future soft robotics' biocompatibility and functionality requirements.

Terahertz vortex beam propagation through a magnetized plasma-ferrite structure

Interaction of vortex beams with materials has proven to be a key for controlling and exploiting theirs properties. In this paper, we propose an adjustable stratified structure constructed from plasma and ferrite layers, which greatly manipulates the intensity and phase distributions of incoming terahertz vortex beam (TVB), and demonstrates a considerable amount of Faraday rotation. To obtain the output beam profiles, first using angular spectral expansion technique the incoming TVB is decomposed into a superposition of plane waves, then employing 4×4 matrix formalism total reflection and transmission coefficients are extracted. Numerical analysis reveals that how the variations of external static magnetic field, incident angle, and radial and angular indices of the TVB affect the features of reflected and transmitted beams. It is expected that this investigation will shed new light on the interaction of TVB with anisotropic magnetic materials, and open new possibilities for wavefront engineering and material characterization.

Influence of Material Parameters on the Stability of Artificial Skyrmion in Hard/Soft Magnetic Bilayers

Herein, the influence of material parameters on the core diameter of the artificial skyrmions in hard magnetic/soft magnetic bilayer thin film is investigated. It is found that the perpendicular magnetic anisotropy (PMA) constant and the interlayer exchange constant play a key role in the realization of artificial skyrmions. Through simulation, the PMA constant of the hard magnetic materials should be between 1.0 × 105 and 4.5 × 105 J m−3. Therefore, some rare earth materials with high magnetic anisotropy or other materials with low magnetic anisotropy do not meet the requirement. The initial skyrmion spin texture is Bloch‐type artificial skyrmion in the hard/soft magnetic bilayer system. In the presence of 1.0–1.5 × 105 J m−3 PMA constant and 0 J m−1 interlayer exchange constant, the Néel‐type artificial skyrmions are formed in the hard/soft magnetic bilayer system. The size of the hard magnetic layer material has little effect on the stability of skyrmions, so the stability of skyrmions should mainly be adjusted with the PMA of the hard magnetic materials or by changing the material types.

Time-Domain Studies of General Dispersive Anisotropic Media by the Complex-Conjugate Pole–Residue Pairs Model

A novel finite-difference time-domain formulation for the modeling of general anisotropic dispersive media is introduced in this work. The method accounts for fully anisotropic electric or magnetic materials with all elements of the permittivity and permeability tensors being non-zero. In addition, each element shows an arbitrary frequency dispersion described by the complex-conjugate pole–residue pairs model. The efficiency of the technique is demonstrated in benchmark numerical examples involving electromagnetic wave propagation through magnetized plasma, nematic liquid crystals and ferrites.

Eddy Current Sensor System for Tilting Independent In-Process Measurement of Magnetic Anisotropy.

Modern production equipment is based on the results of quality control as well as process parameters. The magnetic anisotropy of materials is closely connected to internal mechanical stress by the Villari effect, and also to hardening effects due to plastic deformations, and could therefore provide an interesting basis for process control. Nevertheless, the analysis of anisotropic properties is extremely sensitive to sensor and workpiece misalignments, such as tilting. In this work, a novel eddy current sensor system is introduced, performing a non-contact measurement of the magnetic anisotropy of a workpiece and realizing a separation and correction of tilting effects. The measurement principle is demonstrated with the example of two samples with different magnetic anisotropy values induced by cold forming. Both samples are analyzed under different tilt angles between the sensor axis and the surface of the workpiece. In this work, digital signal processing is demonstrated on the acquired raw data in order to differentiate the effects of tilt and of anisotropy, with the use of preliminary results as an example of two prepared samples.

Controllable preparation and microwave absorption properties of shape anisotropic Fe3O4 nanobelts

To substantially prevent electromagnetic threatens, microwave absorbing materials (MAMs) are required to eliminate surplus electromagnetic waves. As a typical MAM, Fe3O4 particles with complex permittivity and permeability have been widely applied due to the coexistence of magnetic loss and dielectric loss. However, the necessary high mass fraction significantly limited its applications, thus Fe3O4 nanostructures have been extensively investigated to overcome this problem. In this work, uniform Fe3O4 nanobelts were prepared by electrospinning and two-step thermal treatment. By controlling the composition and viscosity of the electrospinning precursor solution, Fe3O4 nanobelts with tunable lateral sizes (200 nm–1 μm) were obtained. The samples with low content (only 16.7 wt%) Fe3O4 exhibited wide maximum effective absorbing bandwidths (EAB) over 3 GHz, and Fe3O4 nanobelts with smaller lateral sizes showed a maximum EAB of 4.93 GHz. Meanwhile, Fe3O4 nanobelts with smaller lateral sizes presented superior reflection loss properties, the lowest reflection loss reached −53.93 dB at 10.10 GHz, while the maximum EAB was up to 2.98 GHz. The excellent microwave reflection loss of Fe3O4 nanobelts was contributed to the enhanced synergistic effect of magnetic loss, dielectric loss, and impedance matching, originated from the hierarchically cross-linked networks and shape anisotropies. This study could broaden the practical applications of magnetic absorbers, and provided an approach for the development of shape anisotropic magnetic materials.

Orientation control of optical mode ferromagnetic resonance: From uniaxial to omni-directional

Both high ferromagnetic resonance frequency (fr) and homogeneous angular performance are important for soft magnetic films to be used in high-frequency integrated circuit devices. However, high fr are obtainable only along the easy axis direction of the magnetic anisotropic materials. In uniaxially anisotropic FeCoB/Ru/FeCoB films, we could obtain an ultrahigh optical mode ferromagnetic resonance frequency (frO) up to 19.16 GHz along the easy axis under a self-bias field due to the enhancement from strong interlayer exchange coupling. However, the uniaxial intensity distribution of optical mode resonance seriously hinders the practical application in microwave components. In order to obtain the desired homogeneous angular performance, soft magnetic films with widely distributed magnetic anisotropy directions in the films were prepared and a nearly omni-directional frO with uniform values around 13.5 GHz was achieved. This study demonstrates that controlling the magnetic anisotropy's angular distribution is an effective way to obtain isotropic, self-bias magnetic films with ultrahigh fr.

Spin and orbital properties of perpendicular magnetic anisotropy for spin-orbit torque material devices

Computer engineers have been attempting to incorporate spin-based devices in future computer architectures, such as processing-in-memory (PIM) in artificial intelligence systems. A successful PIM requires ongoing efforts for developing fast and low-power spintronic material devices. The spin-orbit torque (SOT) device, which is associated with perpendicular magnetic anisotropy (PMA) materials, is a promising candidate. Herein, macroscopic and nanoscopic studies on the spin-orbit interaction of two distinct SOT-PMA systems are conducted to enhance our understanding of the interfacial PMA and pave the way of material design for reliable and high-performance spin memory and logic devices. The experimental results indicate that further theoretical studies are needed to establish a sophisticated explanation instead of the conventional hybridization for the interfacial PMA. In addition, an interesting phenomenon, which can be a useful ingredient while applying thermal energy barrier, concerning the integration of reliable spin devices in future commercial computer systems is reported.

Сверхбыстрое лазерно-индуцированное управление магнитной анизотропией наноструктур

Employing short laser pulses with a duration below 100 fs for changing magnetic state of magnetically-ordered media has developed into a distinct branch of magnetism —femtomagnetism which aims at controlling magnetization at ultimately short timescales. Among plethora of femtomagnetic phenomena, there is a class related to impact of femtosecond pulses on magnetic anisotropy of materials and nanostructures which defines orientation of magnetization, magnetic resonance frequencies and spin waves propagation. We present a review of main experimental results obtained in this field. We consider basic mechanisms responsible for a laser-induced change of various anisotropy types: magnetocrystalline, magnetoelastic, interfacial, shape anisotropy, and discuss specifics of these processes in magnetic metals and dielectrics. We consider several examples and describe features of magnetic anisotropy changes resulting from ultrafast laser-induced heating, impact of laser-induced dynamic and quasistatic strains and resonant excitation of electronic states. We also discuss perspectives of employing various mechanisms of laser-induced magnetic anisotropy change for enabling processes prospective for developing devices. We consider precessional magnetization switching for opto-magnetic information recording, generation of high-frequency strongly localized magnetic excitations and fields for magnetic nanotomography and hybrid magnonics, as well as controlling spin waves propagation for optically-reconfigurable magnonics. We further discuss opportunities which open up in studies of ultrafast magnetic anisotropy changes because of using short laser pulses in infrared and terahertz ranges.

Temperature-dependent magnetic transitions in CoCrPt-Ru-CoCrPt synthetic ferrimagnets

The magnetic orientations and switching fields of a CoCrPt-Ru-CoCrPt synthetic ferrimagnet with perpendicular magnetic anisotropy have been studied in the temperature range from 2 K to 300 K. It was found that two sets of magnetic transitions occur in the CoCrPt-Ru-CoCrPt ferrimagnet across this temperature range. The first set exhibits three magnetic transitions in the 50 K–370 K range, whereas the second involves only two transitions in the 2 K and 50 K range. The observed magnetic hysteresis curves of the synthetic ferrimagnet are explained using the energy diagram technique framework pioneered by Koplak et al. [1] which accurately describes the competition between interlayer exchange coupling energy, Zeeman energy, and anisotropy energy in the system. In this work we expand the framework to include synthetic ferrimagnets (SFMs) comprising higher perpendicular magnetic anisotropy materials and large (4X) interlayer exchange coupling energies which are promising for the development of ultrafast (ps) magnetic switching free layers in MTJ structures. Furthermore, we apply the analysis to predict SFM magnetic hysteresis curves in a temperature regime that includes temperature extrema that a synthetic ferrimagnet would be expected to reliably operate at, were it to be utilized as a free layer in a memory or sensor spintronic device.