Amorphous Magnets Research Articles

Amorphous quantum magnets in a two-dimensional Rydberg atom array

Amorphous quantum magnets in a two-dimensional Rydberg atom array

Accurate calculation of losses in amorphous alloy cores based on a dynamic Jiles-Atheron model under wide frequency and variable temperature operating conditions

The stator core of the high-speed amorphous alloy permanent magnet synchronous motor(HSAAPMSM）experiences significant temperature fluctuations due to exposure to a high-frequency alternating magnetic field. We introduce the dynamic Jiles-Atheron(J-A) model under wide frequency and variable temperature operating conditions to achieve accurate modeling for stator core loss. In contrast to previous modeling techniques, this approach does not rely on amount of experience data and laborious parameter identifications. The adaptive chaotic dung beetle optimization algorithm is applied to improve the effectiveness of parameter identification. The temperature-dependent static J-A model is modified into a dynamic J-A model by combining the field separation approach with the Riemann-Liouville (R-L) fractional derivative theory to enable the model's application under high-frequency operating circumstances. Finally, the model described in this study is verified through experimentation and can be used to precisely calculate the loss of amorphous alloy cores.

Revealing the role of Co element on local structure and magnetism in Fe-Si-B-C amorphous alloys through calculations and experiments

In order to understand the role of Co element on glass-forming ability(GFA) and magnetization of Fe-Si-B-C amorphous alloys, we analyse atomic structures, electronic structure and magnetic moments by ab initio molecular dynamics simulations.The GFA and magnetization of (Fe0.8Co0.2)83.6Si1B15C0.4 amorphous alloy are best in our experiment and simulation. According to calculations of the local structures, electronic structures, and magnetic moments,Fe-centered or Co-centered deformed body-centered cubic units and B-centered prism units predominate in the local structures of Fe-Co-Si-B-C amorphous alloys. In particular, the ratio of Co to Fe of 1:4 in (Fe0.8Co0.2)83.6Si1B15C0.4 amorphous alloy is the critical factor for enhancing GFA and magnetization, which improves the degree of atomic chaos, the stability of the local atomic structures and enhances magnetic moments. However, the excessive addition of Co leads glass-forming ability and magnetization to reduce.This work offers insight into the relationship between local atomic structures and Fe-Co-based amorphous alloy magnetization and offers suggestions for the development of high-performing soft-magnetic amorphous alloys.

Analysis of vibration characteristics of amorphous alloy permanent magnet synchronous motor considering magnetostriction effect

Analysis of vibration characteristics of amorphous alloy permanent magnet synchronous motor considering magnetostriction effect

Relationship among intrinsic magnetic parameters and structure and crucial effect of metastable Fe3B phase in Fe-metalloid amorphous alloys

The intrinsic heterogeneity of an amorphous structure originates from composition, and the structure determines the magnetic properties and crystallization models of amorphous magnets. Based on classical Fe–B binary magnetic amorphous alloys, the relationship between the structure and magnetic properties was extensively studied. The stacking structure of Fe–B binary amorphous alloys exhibit discontinuous changes within the range of 74–87 at.% Fe. The structural feature can be expressed as Amor. Fe3B matrix + Fe atoms are transforming into Amor. Fe matrix + B atoms with the increase of Fe content. The solute atoms are uniformly distributed in the amorphous matrix holes, similar to a single-phase solid solution structure. The transition point corresponds to the eutectic crystallization model composition (Fe82B18 to Fe83B17). A high Fe content will amplify magnetic moment sensitivity to temperature. Under a given service temperature, the disturbance effect of magnetic moment self-spinning will offset the beneficial effect of increasing Fe content and induce the saturation magnetization (Ms) value to decrease. Binary amorphous Fe–B alloys obtain the maximum Curie temperature near 75 at.% Fe, which is slightly smaller than that of the corresponding metastable Fe3B phase, i.e., the amorphous short-range order structure maintains the highest similarity to the Fe3B phase. The chemical short-range ordering (SRO) structure of amorphous alloys exhibits heredity to corresponding (meta)stable crystal phases. The unique spatial orientation structure of the metastable Fe3B phase is the structural origin of the amorphous nature. This study can guide the composition design of Fe-metalloid magnetic amorphous alloys. The design of materials with excellent magnetic properties originates from a deep understanding of precise composition control and temperature disturbance mechanism.

Developing High-Power-Density Electromagnetic Devices with Nanocrystalline and Amorphous Magnetic Materials

With the increasing demand for smaller, lighter, and more affordable electromagnetic devices, there is a growing trend toward developing high-power-density transformers and electrical machines. While increasing the operating frequency is a straightforward approach to achieving high power density, it can lead to significant power loss within a limited volume, resulting in excessive temperature rise and device degradation. Therefore, it is crucial to design high-power-density electromagnetic devices that exhibit low power loss and efficient thermal dissipation to address these challenges. Advanced techniques, such as the utilization of novel and advanced electromagnetic materials, hold great promise for overcoming these issues. Specifically, nanocrystalline and amorphous magnetic materials have emerged as highly effective solutions for reducing power loss and increasing efficiency in electromagnetic devices. This paper aims to provide an overview of the application of nanocrystalline and amorphous magnetic materials in transformers and electrical machines, along with key technologies and the major challenges involved.

Magnon spectrum of the amorphous ferromagnet Co4P from atomistic spin dynamics

An anomaly in the magnon dispersion of the amorphous ferromagnet Co$_{4}$P, often referred to as a `roton-like' excitation, attracted much attention half a century ago. With the current interest in heat and spin currents in amorphous magnets, we apply modern simulation methods, combining reverse Monte Carlo to build the atomic structure and the stochastic Landau-Lifshitz equation for spin dynamics, to re-investigate the magnetic excitation spectrum. We find two magnon valleys, one at the origin and another at a finite wavenumber close to the observations, but without a magnon gap. We conclude that the second dip is due to Umklapp scattering caused by residual long-range order, which may be an alternative explanation of the putative roton excitation. Our study paves the way to study magnon transport in amorphous magnets and related spintronic applications.

Determination of small magnitudes of magnetostriction in amorphous microwires with an arbitrary type of magnetic anisotropy

The magnetic anisotropy and magnetic structure of amorphous ferromagnets are largely determined by magnetoelastic interactions due to the absence of magnetocrystalline anisotropy, e.g., in amorphous microwires with a glass sheath, the source of anisotropy is the mechanical stresses that arise in the ferromagnetic core upon manufacturing. Hence, to control the magnetic structure and magnetization reversal processes occurred in amorphous magnetics, it is necessary to know the magnetostriction coefficient of the material. We propose an improved approach to measuring extremely small values of the magnetostriction coefficient of ferromagnetic microwires with an arbitrary type of magnetic anisotropy and magnetic microstructure. The samples of amorphous wires in a glass sheath made of Co67Fe5B12Si14Cr3 alloys were studied. The type of magnetic anisotropy of the samples (from axial to circular) was changed using current annealing. The developed method is based on small-angle precession of magnetization around the wire axis, resulted from the effect of the axial magnetic field induced by an alternating current passed through the wire. A voltage signal generated in a detection coil wound around the sample at a frequency doubled with respect to the frequency of the alternating current was recorded using a lock-in amplifier. When exposed to external mechanical loads, the voltage signal changes, and an additional axial magnetic field (bias field) is required to maintain a constant level of this signal. The value of magnetostriction is determined from the dependence of the displacement field on mechanical loads. The maximum sensitivity of measurements in the range of 10–8 – 10–7 is achieved at a uniform magnetization, increased frequency of the alternating current, and high value of the ratio between the length and diameter of tested wire samples. The sign and magnitude of the magnetostriction constant change upon current annealing which correlates with modification of the magnetization curves. The results obtained can be used to determine and adjust the parameters of the actuators developed on the basis of the considered microwires (in particular, microsensors of mechanical stresses and microactuators).

Controlling crackling dynamics by triggering low-intensity avalanches.

We examine the effect of small, spatially localized excitations applied periodically in different manners, on the crackling dynamics of a brittle crack driven slowly in a heterogeneous solid. When properly adjusted, these excitations are observed to radically modify avalanche statistics and considerably limit the magnitude of the largest events. Surprisingly, this does not require information on the front loading state at the time of excitation; applying it either at a random location or at the most loaded point gives the same results. Subsequently, we unravel how the excitation amplitude, spatial extent, and frequency govern the effect. We find that the excitation efficiency is ruled by a single reduced parameter, namely the injected power per unit front length; the suppression of extreme avalanches is maximum at a well-defined optimal value of this control parameter. analysis opens another way to control the largest events in crackling dynamics. Beyond fracture problems, it may be relevant for crackling systems described by models of the same universality class, such as the wetting of heterogeneous substrates or magnetic walls in amorphous magnets.

Computer aided design of amorphous alloy permanent magnet motor

Amorphous alloy is a kind of double green soft magnetic material with high saturation magnetic induction, low coerce, low loss, high stability and other excellent properties. Instead of cold rolled silicon steel sheet, it can reduce the loss and improve the efficiency of the motor to a great extent. Combined with the characteristics of amorphous alloy and based on the design theory of permanent magnet motor, this paper uses the MATLAB software to write the electromagnetic design program of amorphous alloy permanent magnet synchronous motor, which has the characteristics of visual parameter input, rapid electromagnetic calculation, and convenient man-machine interaction. An example is given to verify the reliability of the program.

Amorphous exchange-spring magnets with crossed perpendicular and in-plane anisotropies

We study the magnetic coupling in a thin film bilayer exchange-spring magnet composed of an amorphous ${\mathrm{Tb}}_{10}{\mathrm{Co}}_{90}$ layer with a large perpendicular anisotropy and an amorphous ${\mathrm{Co}}_{85}{({\mathrm{Al}}_{70}{\mathrm{Zr}}_{30})}_{15}$ layer with uniaxial in-plane anisotropy. The CoAlZr is directly exchange coupled to the TbCo with an interface region of at least 7.5 nm within which the CoAlZr magnetization is perpendicular to the plane and switches with the underlying TbCo. The influence of the coupling extends up to 30 nm into the CoAlZr resulting in an effective tilted anisotropy. The coercivity of the CoAlZr is greatly enhanced due to the coupling and is tuneable over a large range by varying its thickness.

ОСОБЕННОСТИ МАГНИТНОГО СОСТОЯНИЯ В АМОРФНЫХ МАГНЕТИКАХ RE–TM и RE–TM–B (обзор)

Provides an overview of the magnetism features of amorphous magnets of the RE–TM and RE–TM–B alloys (RE – rare earth metal, TM – transition metal, B – boron). Magnetic states in amorphous alloys, the effect of the single-ionic anisotropy of heavy rare-earth metals on local disorder and spin frustrations in an amorphous body, and some spin-reorientation transitions observed in such compounds are presented. It is shown that the identification of the spin-glass state can be achieved by detecting specific features on the field and temperature dependences of the magnetic moment and magnetic susceptibility of the sample.

Rigid Exchange Coupling in Rare‐Earth‐Lean Amorphous Hard/Soft Nanocomposites

AbstractElectrification of vehicles and renewable energy is increasing the demand for permanent magnets, but the cost and scarcity of rare‐earth metals is an obstacle. Creating nanocomposites of rigidly exchange‐coupled hard and soft magnets, for which the magnetization reversal occurs as in a single magnetic‐phase material, is a promising route toward rare‐earth‐lean permanent magnets with high energy products. The hard/soft exchange coupling is, however, often reduced due to rough interfaces and structural defects, resulting in exchange‐spring behavior rather than rigid exchange coupling. Here, it is shown that artificially sandwiched hard and soft amorphous magnets produced by magnetron sputtering exhibit smooth interfaces, and the first order reversal curve (FORC) technique is used to show that the hard and the soft phases are rigidly exchange coupled. Micromagnetic simulations, using a random‐anisotropy model, are used to predict the thickness limit of the rigid exchange coupling. A great advantage of amorphous hard/soft composites is the possibility to obtain a wide range of magnetic properties by finely tuning the composition of the individual phases.

Direct observation of magnetic proximity effects in amorphous exchange-spring magnets by neutron reflectometry

In this letter we report a direct observation of a magnetic proximity effect in an amorphous thin film exchange-spring magnet by the use of neutron reflectometry. The exchange-spring magnet is a trilayer consisting of two ferromagnetic layers with high $T_c$'s separated by a ferromagnetic layer, which is engineered to have a significantly lower $T_c$ than the embedding layers. This enables us to measure magnetization depth profiles at which the low $T_c$ material is in a ferromagnetic or paramagnetic state, while the embedding layers are ferromagnetic. A clear proximity effect is observed 7 K above the $T_c$ of the embedded layer, with a range extending 50 $\unicode{xC5}$.

Magnet eddy-current losses reduction of an axial-flux in-wheel motor with amorphous magnet metal

The yokeless and segmented armature axial-flux in-wheel motor with amorphous magnet metal (AMM) stator segment has the advantage of low iron losses, but its open-slot structure causes high eddy-current losses of the permanent magnet (PM), which reduces the efficiency and reliability of the in-wheel motor. To avoid the demagnetization caused by the heat generated by PM losses, the mechanism of PM eddy-current losses reduction for the axial-flux in-wheel motor is revealed by the calculation model. In this paper, the time-step three-dimensional finite-element method (3-D FEM) is used to analyze the PM eddy-current loss caused by slotting effects, spatial harmonics, and time harmonics at different speeds. The effect of PM skewing, PM segmentation, and soft magnetic composite (SMC) layer inserted on the top of PM on eddy-current losses are compared. These methods cannot simultaneously meet the requirements of PM losses reduction and the electromagnetic performance of the motor. A novel combined stator segment with the SMC brim arranged on the top of the AMM stator teeth is proposed to improve the amplitude and distribution of the PM eddy-current density. The analysis results show that the combined stator segment can significantly reduce the PM eddy-current loss and improve the electromagnetic performance of the in-wheel motor.

Speromagnetism and asperomagnetism as the ground states of the Tb-Dy-Ho-Er-Tm “ideal” high-entropy alloy

We address the nature of the collective magnetic state in an ideal high-entropy alloy (HEA), representing a magnetically concentrated system with all lattice sites occupied by localized magnetic moments and containing randomness and frustration due to chemical disorder. Being a “metallic glass on a topologically ordered lattice”, HEAs possess simultaneously the properties of an ordered crystal and an amorphous glass. The influence of this crystal-glass duality on the collective magnetic state was studied experimentally on a hexagonal Tb-Dy-Ho-Er-Tm (TDHET) HEA, composed of rare-earth (RE) elements with zero pair mixing enthalpies that assure completely random mixing of the elements and very similar atomic radii that minimize lattice distortions, representing a prototype of an ideal HEA. The TDHET HEA is characterized by probability distributions of the atomic moments P(μ), the exchange interactions P(J), the magnetocrystalline anisotropy P(D), and the dipolar interactions P(Hd). Based on the measurements of the static and dynamic magnetization, the magnetization M(H) curves, the thermoremanent magnetization, the specific heat and the magnetoresistance, we found that the collective magnetic state of the TDHET is temperature-dependent, forming a speromagnetic (SPM) state in the temperature range between about 140 and 30 K and an asperomagnetic (ASPM) state below 20 K. In the intermediate temperature range between 30 and 20 K, a spin glass (SG) state is formed, representing a transition state between the speromagnetic and asperomagnetic states. The observed temperature evolution of the magnetic ground state in the TDHET HEA upon cooling in the sequence SPM→SG→ASPM is a result of temperature-dependent, competing magnetic interactions. The distribution of the exchange interactions P(J) shifts continuously on the J axis from the high-temperature SPM-type with the average interaction biased towards a net negative value, J‾<0, through the SG-type with J‾=0, to the low-temperature ASPM-type with J‾>0. This shift is a band-structure effect, closely linked with the crystallinity of the spin system, which the TDHET HEA shares with the topologically ordered crystals. The probability distributions P(μ), P(J), P(D) and P(Hd) are, on the other hand, a consequence of chemical disorder, a property that the TDHET HEA shares with the amorphous magnets. Both features, the topologically ordered lattice and the amorphous-type chemical disorder essentially determine the magnetic state of an ideal, RE-based HEA.

Hydrodynamics of three-dimensional skyrmions in frustrated magnets

We study the nucleation and collective dynamics of Shankar skyrmions [Shankar, J. Phys. 38, 1405 (1977)] in the class of frustrated magnetic systems described by a SO(3) order parameter, including multilattice antiferromagnets and amorphous magnets. We infer the expression for the spin-transfer torque that injects skyrmion charge into the system and the Onsager-reciprocal pumping force that enables its detection by electrical means. The thermally assisted flow of topological charge gives rise to an algebraically decaying drag signal in nonlocal transport measurements. We contrast our findings to analogous effects mediated by spin supercurrents.

Giant magnetic proximity effect in amorphous layered magnets

Here we study the magnetic proximity effect in amorphous layered magnets of alternating high- and low-${T}_{\text{c}}$ materials using magnetometry and polarized neutron reflectivity. By altering the thickness of either the high- or low-${T}_{\text{c}}$ layer we are able to extract the induced magnetic moment in the low-${T}_{\text{c}}$ layer directly and study how it scales with thickness. We observe that the ordering temperature of the low-${T}_{\text{c}}$ layer is enhanced and above which a second magnetically ordered state with a very large extension is observed. This induced magnetic state survives to a temperature at least three times that of the ordering temperature of the low-${T}_{\text{c}}$ layer and the induced magnetization is approximately constant throughout at least a 10-nm-thick layer. The induced magnetic region within the low-${T}_{\text{c}}$ layer does not depend on the thickness of the adjacent high-${T}_{\text{c}}$ layer.

Monte Carlo simulation of amorphous magnets with random exchange interactions

Using the Monte Carlo method, the computer simulation of magnetic properties of pure amorphous Gd and Re-Gd amorphous alloys was performed. For the model of amorphous Gd the temperature dependencies of magnetization and magnetic susceptibility were calculated at different values of the ratio of exchange interaction integrals wihin the first and the second coordination spheres J1/|J2| . The magnetic phase diagram in coordinates T - J1/|J2| was constructed. For the models of Re-Gd amorphous alloys the dependence of spin-glass transition temperature on concentration of Gd atoms was calculated. For all our models the hysteresis loops were calculated at different temperatures.

Development and study of a dynamic model of single-phase amorphous steel core transformer

The use of amorphous ferromagnetic alloys in transformer construction allows reducing no-load losses by 4 times or more. At the same time, the magnetization curve of amorphous steel has a shape that is close to a rectangle, which significantly distorts the shape of the no-load current curve. This is accompanied by inrush current increases when a saturated transformer is turned on. However, there are no publications devoted to this issue in the periodicals. The purpose of this work is to develop a dynamic model and study the dynamics of an amorphous steel core single-phase transformer (TAS) operating at an arbitrary external load. The calculation of the electrical circuit was made by a one-step method based on a modified 2nd-order Rosenbrock formula, and the circuit parameters were calculated by the finite element method. We have developed dynamic models of the single-phase transformer based on the use of controlled current sources and EMF and implemented in the MatLab Simulink SimPowerSystem. These models allowed us to take into account the effect produced by the practically rectangular shape of the magnetization curve of the amorphous steel used to make the core on the operation of a saturated transformer. It has been established that the inrush current occurring when a saturated TAS is switched on can exceed the rated current tenfold. A significant distortion of the current curve has been detected in the first periods even when the transformer operates at nominal load. The developed models can be used to study the operation of a transformer at an arbitrary load. These models can be developed further. It has been found that a significant effect on the transformer operation is produced by the shape of the amorphous steel magnetization curve.