Ferromagnetic Structure Research Articles

Handle on the antiferromagnetic spin structure of NiO using a ferromagnetic adlayer

Antiferromagnets (AFs) are characterized by spin structures that are resistant to external magnetic fields, rendering them ideal for persistent information storage but challenging to control. This study demonstrates that a thin ferromagnetic adlayer can serve as a magnetic ‘lever’ to provide a strong handle on the spin texture of an adjacent antiferromagnet. In bilayers composed of NiO(001) and Co, the expected exchange bias effect—a unidirectional shift in the Co hysteresis due to coupling with NiO—is notably absent. Instead, a strong interfacial coupling is observed, causing the NiO to partially follow the magnetization of Co under an applied magnetic field. Using x-ray magnetic linear dichroism, we detect an inversion of dichroism, indicating a reorientation of the Néel vector in NiO. X-ray spectromicroscopy imaging further reveals a direct correlation between ferromagnetic and antiferromagnetic domain structures. These findings are explained using a toy model that distinguishes between stable and unstable AF domains, highlighting the dynamic interplay between NiO and the Co adlayer in the presence of a magnetic field. Published by the American Physical Society 2025

First-principles study of robust half-metallic ferromagnetism and electronic structure of the Heusler compounds Co2-xCrxMnGe

Abstract Half-metallic ferromagnets (HMFs) are among the most promising materials in the field of spintronics because of their distinct band structures, which consist of two characteristic subbands, one with semiconductor-like behaviour and the other with metallic features. Using density functional theory-based calculations, we have carried out in-depth studies to predict the effects of Co replacement by Cr on electronic structure as well as the magnetic properties of Co2-xCrxMnGe with 0 ≤ x ≤ 1. The results demonstrate that the alloys are stable in the ferromagnetic phase with half-metallic nature. The origin of ferromagnetism can be explained by Ruderman-Kittel-Kasuya-Yosida (RKKY), like exchange interaction. Due to their high Curie temperatures, which increase linearly with the total magnetic moment, all alloys are suitable for applications at and above room temperature. Besides, the electronic properties have revealed a transition from half-metallic to semi-metallic character for higher doping concentration (x = 0.75, x = 1.0). The calculated total magnetic moments, however, decrease with increasing doping concentration, consistent with the Slater-Pauling rule. The observed high value of spin polarisation of all the studied compounds suggests their futuristic roadmaps for possible spintronics applications beyond room temperature.

Director Response of Liquid Crystals in Spatially Varying Magnetic Fields with Antagonistic Anchoring Conditions.

In the presence of a magnetic field, a liquid crystal (LC) director can be distorted from a ground state set by a combination of LC elasticity and surface anchoring at any relevant interfaces. Uniform magnetic fields are often used to produce simple LC distortions on demand, but producing more spatially complex distortions is practically challenging. We develop a strategy for the spatially resolved control of the LC director by leveraging field patterns induced by ferromagnetic materials. Patterned magnetic fields are generated from high-permeability ferromagnetic microstructures embedded into nematic liquid crystals (NLCs) to manipulate the LC director's orientation. Each ferromagnetic microstructure produces a unique spatially varying magnetic field. In turn, tuning magnetic field strength in competition with NLC elasticity can pattern a range of spatially complex director configurations. Simulations relate the spatial variation induced in a magnetic field by a ferromagnetic geometry and the resultant director. Our predictive models can inform the inverse design of ferromagnetic microstructures to generate bespoke director patterns. We also link changes in the magnetic field to the migration of elastically driven periodic extinctions in birefringence near the edges of ferromagnetic structures.

Magnetic domain walls interacting with dislocations in micromagnetic simulations

Defects, impurities, and embedded particles in ferromagnetic materials are long known to be responsible for the Barkhausen effect due to the jerky field-driven motion of domain walls and have more recently been shown to play a role also in domain wall dynamics in nanoscale ferromagnetic structures used in spintronics devices. Simulating the magnetic domain wall dynamics in the micromagnetic framework offers a straightforward route to study such systems and phenomena. However, the related work in the past suffers from material imperfections being introduced without proper physical foundation. Here, we implement dislocation stress fields in micromagnetic simulations through the induced anisotropy fields by inverse magnetostriction. The effects of individual dislocations on domain wall dynamics in thin films of different Fe surface lattice planes are characterized numerically. As a demonstration of the applicability of the implementation, we consider disorder fields due to randomly positioned dislocations with different densities, and study the avalanche-like transient approach towards the depinning transition of a domain wall driven by a slowly increasing external magnetic field.

Limiting possibilities of detecting cracks in ferromagnetic structures through an anti-corrosion coating using a smartphone based eddy current flaw detector

Detection of cracks in ferromagnetic steel structures by the eddy current method is often limited by additional noise associated with magnetic and structural heterogeneity, especially when it is necessary to detect structural cracks through a layer of dielectric anti-corrosion coating. A promissing approach to problem solution is based on the use of selective eddy current probes, which include the eddy current probes of double differential type. One of the features of such eddy current is the possibility of detecting hidden defects even through a layer of dielectric anti-corrosion coating. In this paper, the limiting possibilities of crack detection using an improved low-frequency eddy current probe of double-differential type with a diameter of 15 mm and a smartphone based eddy current flaw detector were investigated. This probe provides a high depth of penetration necessary to detect defects under the dielectric coating. The greater depth of penetration of this probe is achieved by increasing the diameter of the windings, the distance between them and the number of turns. The research was carried out using a rectangular specimen, in which a large crack (or through wall structure fracture) was simulated by a joint of two identical polished rectangular parts. The assembled specimen was covered with dielectric plates of different thicknesses up to 25 mm thick to simulate anti-corrosion coating of different thicknesses. It is shown, in particular, the possibility of detecting large cracks or structural fractures through an anti-corrosion dielectric coating up to 25 mm thick. The principle of design of an eddy current flaw detector based on a smartphone using the EddySmart application, which can provide remote control of ferromagnetic steel structures with wireless transmission of inspection results via mobile communication channels and the use of autonomous automated scanners, is considered.

Wall thinning quantification with a lift-off distance for ferromagnetic structures using pulsed ECT equipped with ICA-Gauss filter and Hough Transform

Determining the thickness of ferromagnetic materials with a lift-off distance poses a significant challenge for current non-destructive testing (NDT) techniques. Pulsed eddy current (PEC) testing is deemed as a powerful candidate to evaluate this type of defect. However, the signal-to-noise ratio (SNR) of the PEC response signal obtained with large lift-off distance is very poor, so that the signal feature can hardly be extracted. To improve the SNR of PEC response signals and capture the signal feature adaptively, this paper proposed a novel PEC signal processing algorithm based on ICA-Gauss filter and Hough Transform (HT). Firstly, the principle of the proposed method was introduced. Then, two case studies, a comparison experiment and an application experiment were conducted to verify the effectiveness and accuracy of this method. Results from these experiments show that (a) the ICA-Gauss filter can effectively suppress the power-line noises and random noises in PEC signals, (b) the ICA-Gauss filter outperforms traditional filters in feature robustness and computing efficiency, including double-logarithmic median filter and Savitzky-Golay filter, and (c) HT is an adaptive and accurate method to extract the PEC signal feature, thus achieving a small detection error.

Half-metallic ferromagnetism and electronic structure of GeKX (X = Ca, Sr) alloys: a DFT-mBJ approach

Half-metallic ferromagnetism and electronic structure of GeKX (X = Ca, Sr) alloys: a DFT-mBJ approach

Nonreciprocal transmission of surface acoustic waves induced by magneotoelastic coupling with an anti-magnetostrictive bilayer

In this study, we report giant nonreciprocal transmission of shear-horizontal surface acoustic waves (SH-SAWs) in a ferromagnetic bilayer structure with negative–positive magnetostriction configuration. Although the directions of magnetization in the neighboring layers are parallel, SH-SAWs can excite optical-mode spin waves (SWs) via magnetoelastic coupling at relatively low frequencies, which is much stronger than acoustic-mode SWs at high frequencies. The measured magnitude nonreciprocity or isolation of SH-SAWs exceeds 40 dB (or 80 dB/mm) at 2.333 GHz. In addition, maximum nonreciprocal phase accumulation reaches 188° (376°/mm). Our theoretical model and calculations provide an insight into the observed phenomena and demonstrate a pathway for further improving nonreciprocal acoustic devices toward highly compact microwave isolators and circulators.

Control of the light polarization in ferromagnetic diode structures InGaAs/GaAs/δ-Mn

Electric-field influence on the polarization of the quantum well photoluminescence is studied in the diode structures InGaAs/GaAs/δ-Mn with narrow GaAs spacer dS = 2–5 nm at small magnetic field. Weakening of the circular polarization degree with increasing electric-field evidence about significant contribution of the stationary mechanism of the carriers’ polarization due to their exchange coupling with a nearby ferromagnetic δ-Mn-layer.

Structural, thermodynamic, magnetic and electronic properties of novel bromide double perovskites Rb2XBr6 (X4+ = V4+, Cr4+, Mn4+) from first-principles DFT computational modeling

The structural, thermodynamic stability, magnetic, and electronic characteristics of rubidium-based bromide double perovskites Rb2XBr6 (X4+ = V4+, Cr4+, Mn4+) have been verified to be explained using density functional theory (DFT) computations. The Perdew-Burke-Ernzerhof functional in generalized gradient approximation (PBE-GGA) is implemented to treat the exchange-correlation. The structural optimization, formation energy, tolerance factor, and thermodynamic demonstrate the reliability and stability of all Rb2XBr6 in face-centered cubic structure (Fm-3m). Spin-polarized band structures and density of states show the presence of half-metallic, semimetallic, and semiconductor nature in Rb2XBr6 materials, respectively. Additionally, we investigated the magnetic moments of Rb2XBr6 and the genesis of ferromagnetic and electronic structures in these systems. It found that Rb2XBr6 possess an integer total magnetic moment of 1.0 μB (X4+ = V4+), 2.0 μB (X4+ = Cr4+), and 3.0 μB (X4+ = Mn4+), where the 3d-orbitals of X4+ contribute the up majority of magnetic moments. The significant electronic and ferromagnetic properties are attributed to the unpaired electrons in V-3d3, Cr-3d5, and Mn-3d5. The PBE-GGA computations reveal that the ferromagnetic Curie temperature of Rb2XBr6 is 204 K, 387 K and 566 K, respectively. The obtained results show that Rb2XBr6 are reliable inorganic materials and candidates for spintronics and optoelectronics technologies.

First-principles calculations to investigate optoelectronic of transition-metal half-Heusler alloys MTiSn (M = Pd and Pt) for optoelectronics applications

The structural, mechanical, optical, and electronic properties of half-Heuslers MTiSn (M = Pd and Pt) are investigated using FP-LAPW incorporating the GGA-PBE. MTiSn crystallize in ferromagnetic (FM) and cubic structure (F-43m; C1b) with lattice constants of 6.216 Å and 6.241 Å, respectively, in good agreement with the available data. Elastic constants Cij reveal that MTiSn meet the mechanical stability criteria with notable thermodynamic properties. Also, we have conducted a detailed analysis of optical properties, encompassing the dielectric function, absorption coefficient, optical conductivity, optical refractivity, and extinction coefficient. It is found that PtTiSn shows higher optical responses than PdTiSn at low and high energy ranges. In terms of electronic properties, MTiSn demonstrate narrow bandgap semiconductor characteristics with an indirect bandgap of Eg = 0.507 eV (M = Pd) and Eg = 0.782 eV (M = Pt). The notable optoelectronic responses have also been examined, indicating the high potential of MTiSn materials for optoelectronic applications.

Eddy Current Mechanism Model for Dynamic Magnetic Field in Ferromagnetic Metal Structures

The degaussing process is crucial for ensuring magnetic protection in ships. It involves the application of oscillating and attenuating magnetic fields to eliminate residual magnetism in the ship’s structure. However, this process can lead to the generation of distorted magnetic fields within the ship’s cabin, posing a potential threat to electronic equipment performance. Therefore, it is essential to have a comprehensive understanding of the dynamic magnetic field response in ship structures to develop effective degaussing systems. To address this need, this paper proposes an eddy current model for analyzing the dynamic magnetic field response in ferromagnetic metal structures. This model focuses on the role of eddy currents in shaping the magnetic field response and provides valuable insights into the underlying mechanisms. Using the proposed eddy current model, the effects of key system parameters such as thickness, conductivity, and the length-scale of the ship structure can be analytically investigated. This analysis helps in understanding how these parameters influence the dynamic magnetic field response and aids in the design and optimization of degaussing systems. The effectiveness and applicability of the proposed eddy current model are demonstrated through comprehensive investigations involving two simulation cases of varying complexity. The model accurately predicts the changing trends of the dynamic magnetic field response, as confirmed through finite element simulations. This validation highlights the model’s ability to reproduce simulation results accurately and its potential as a powerful tool for analyzing and optimizing dynamic magnetic field responses. In summary, the proposed eddy current model represents a significant advancement in the field. It provides a valuable theoretical framework for understanding and analyzing the dynamic magnetic field response in ferromagnetic metal structures. By offering insights into the underlying mechanisms and the influence of key parameters, this research contributes to the development of improved degaussing systems and enhances the overall magnetic protection capabilities of ships.

Reconfigurable spin-wave properties in two-dimensional magnonic crystals formed of diamond and triangular shaped nanomagnets

Two-dimensional ferromagnetic nanodot structures exhibit intriguing magnetization dynamics and hold promise for future magnonic devices. In this study, we present a comparative experimental investigation into the reconfigurable magnetization dynamics of non-ellipsoidal diamond and triangular-shaped nanodot structures, employing broadband ferromagnetic resonance spectroscopy. Our findings reveal substantial variations in the spin wave (SW) spectra of these structures under different bias field strengths (H) and angles (φ). Notably, the diamond nanodot structure exhibits a variation from nearly symmetric W-shaped dispersion to a skewed dispersion and subsequent transition to a discontinuous dispersion with subtle variation in bias field angle. On the other hand, in the triangular nanodot array a SW mode anti-crossing appears at φ = 15° which is starkly modified with the increase in φ to 30°. By analyzing the static magnetic configurations, we unveil the nature of the SW spectra in these two shapes. We reinforce our observations with simulated spatial power and phase maps. This study underscores the critical impact of dot shape and inversion symmetry on SW dynamical response, highlighting the significance of selecting appropriate structures and bias field strength and orientation for required functionalities. The remarkable tunability demonstrated by the magnonic crystals underscores their potential suitability for future magnonic devices.

Magnetic Structure-Dependent Spin Texture Lattice in Hexagonal MnFeCoGe Magnets.

Topological spin textures are of great significance in magnetic information storage and spintronics due to their high storage density and low drive current. In this work, the transformation of magnetic configuration from chaotic labyrinth domains to uniform stripe domains was observed in MnFe1-xCoxGe magnets. This change occurs due to the noncollinear magnetic structure switching to a uniaxial ferromagnetic structure with increasing Co content, as identified by neutron diffraction results and Lorentz transmission electron microscopy (L-TEM). Of utmost importance, a hexagonal lattice of high-density robust type-II magnetic bubble lattice was established for x = 0.8 through out-of-plane magnetic field stimulation and field-cooling. The dimensions of the type-II magnetic bubbles were found to be tuned by the sample thickness. Therefore, the stabilization of complex magnetic spin textures, associated with enhanced uniaxial ferromagnetic interaction and magnetic dipole-dipole interaction in MnFe1-xCoxGe through magnetic structure manipulation, as further confirmed by the micromagnetic simulations, will provide a convenient and efficient strategy for designing topological spin textures with potential applications in spintronic devices.

Enhanced polishing characteristics of Al-6061 via composite magnetic abrasives (EIP–Al2O3) assisted hybrid CMMRF process

In magnetorheological (MR) fluid polishing, high magnet speed releases abrasive particles from the finishing region, reducing their grip on the ferromagnetic chain structure and triggering the process to stall. Enhancing polishing efficiency necessitates developing a new composite magnetic abrasive (EIP-Al2O3) through microwave sintering. EIP-Al2O3 has favourable soft magnetic effects when it comes to its structure, phase composition, magnetic, and rheological properties. Chemo-mechanical magneto-rheological finishing (CMMRF), a developed hybrid-finishing method, aims to thoroughly evaluate CMA's performance. CMA attains a defect-free Al-6061 surface with Ra ∼79 nm and MRR ∼0.379 mg/min. CMAs outperforms simply mixed abrasives (SMA) by a significant 25 % increase in Ra and a remarkable 60 % increase in MRR. CMAs emerges as an effective solution for combating tool aging effects at high rotational speeds.

Disclosing magnetic clusters in the metallic half-Heusler ferromagnet Cr4PtGa17 with a breathing pyrochlore lattice

We report a ferromagnetic resonance (FMR) study of a single crystal of Cr4PtGa17, the first material of a half-Heusler (HH) type with a metallic ferromagnetic breathing pyrochlore structure. The spatial distribution of the magnetic free energy density derived from the FMR data appears to be of a cubic symmetry despite the lower symmetry coordination of magnetic Cr ions. This surprising finding strongly suggests that the Cr4Ga14 structural unit at the Y site of the HH general XYZ formula forms an octahedrally shaped integral magnetic cluster, likely due to strong exchange interaction between the Cr ions via covalent Cr-Ga-Cr bonds. The presence of magnetic clusters within a regular metallic lattice appears to be a new intriguing characteristics of these novel types of HH compounds whereas Cr4PtGa17, at the same time, constitutes the rare example of such metallic pyrochlore-type material.

Room temperature chiral magnetoresistance in a chiral-perovskite-based perpendicular spin valve

Chirality-induced spin selectivity (CISS) allows for the generation of spin currents without the need for ferromagnets or external magnetic fields, enabling innovative spintronic device designs. One example is a chiral spin valve composed of ferromagnetic and chiral materials, in which the resistance depends on both the magnetization direction of the ferromagnet and the chirality of the chiral material. So far, chiral spin valves have predominately employed chiral organic molecules, which have limited device applications. Chiral perovskites, which combine the properties of inorganic perovskites with chiral organic molecules, provide an excellent platform for exploring CISS-based devices. However, previous chiral perovskite-based spin valves exhibited magnetoresistance (MR) only at low temperatures. Here, we report room temperature MR in a chiral spin valve consisting of chiral perovskites/AlOx/perpendicular ferromagnet structures. It is observed that the chiral MR increases with rising temperature, suggesting the crucial role of phonon-induced enhancement of spin–orbit coupling in CISS in our device. Furthermore, we enhanced the chiral MR by introducing chiral molecules with amplified chirality. This highlights the potential of chirality engineering to improve CISS and the associated chiral MR, thereby opening possibilities for chiral spin valves tailored for cutting-edge spintronic applications.

Theoretical perspectives on the electronic, optical, mechanical, magnetic, and anisotropic behaviors of the quaternary Heusler alloys RhFeMnZ and IrMnCrZ (where Z = Si, Ge)

High-spin-polarised materials are the most promising candidates for spintronic devices. Here, the spin-polarised electronic structure, magnetism, mechanical, and optical properties of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) Quaternary Heusler alloys were calculated by first-principles calculations. The calculations show that type III for the RhFeMnSi, RhFeMnGe, and IrMnCrSi and type I for the IrMnCrGe compound configuration is the most stable crystal structure for the studied alloys. The four alloys were found to have a half-metallic ferromagnetic structure with indirect band gaps in the majority spin channels of 0.957, 0.66, 0.745, and 0.891 eV for RhFeMnSi, RhFeMnGe, IrMnCrSi, and IrMnCrGe, respectively. They exhibit an appreciable total magnetic moment of 4 μB for RhFeMnZ (Z = Si, Ge) and 2 μB for IrMnCrZ (Z = Si, Ge). The results show that RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are ferromagnetic half-metals with 100 % spin polarisation. The results of the elastic constants demonstrate the mechanical stability of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) alloys. Optical properties such as dielectric function, absorption, reflectance, optical conductivity, and other optical properties were also probed. In the ultraviolet region, RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are effective absorbers and have a high refractive index. Alloys are promising candidates for potential applications in spintronic devices.

Analytical model of magnetic Barkhausen noise testing on surface-modified ferromagnetic plates with stress distributions

Surface treatment is a critical technology in engineering that enhances the mechanical properties of materials, in which the stress state within the material and the thickness of the surface modification layer are essential for optimizing performance. Magnetic Barkhausen Noise (MBN) serves as an effective nondestructive evaluation technique for ferromagnetic structures. In this work, we develop an analytical model that incorporates the attenuation mechanism of the MBN signal strength, and the strength of the stress-induced magnetic Barkhausen excitation (MBE) as determined by the magneto-mechanical constitutive law of the material. The proposed theoretical model can accurately characterize the MBN signal influenced by internal stresses and surface modification layers, as confirmed by comparison with existing experimental results. The theoretical analysis shows the influence of internal stress fields, layer dimensions, and electromagnetic properties on the MBN signal, revealing a positive relationship between signal intensity and the thickness of surface modification layer and the magnitude of internal stresses. This research provides a valuable reference for interpreting MBN signals and evaluating internal stress distributions for surface-modified ferromagnetic plates.

Inspection of Semi-Elliptical Defects in a Steel Pipe Using the Metal Magnetic Memory Method

Ferromagnetic pipes are widely used for fluid transportation in various industries. The failure of these ferromagnetic pipes due to surface defects can generate industrial accidents, economic losses, and environmental pollution. Non-destructive testing techniques are required to detect these surface defects. An alternative is the metal magnetic memory (MMM) method, which can be employed to detect surface flaws in ferromagnetic structures. Based on this method, we present an analysis of experimental results of the magnetic field variations around five different surface semi-elliptical defects of an ASTM A36 steel pipe. A measurement system of MMM signals is implemented with a rotatory mechanism, a magnetoresistive sensor, a data processing unit, and a control digital unit. The MMM method does not require expensive equipment or special treatment of the ferromagnetic structures. In order to research a potential relationship between the defect sample size and the measured MMM signals, variable defect dimensions are experimentally considered. According to these results, the shape and magnitude of the normal and tangential MMM signals are altered by the superficial semi-elliptical defects. In particular, the maximum and mean tangential components and the maximum and minimum normal components are related to the defect dimensions. The proposed measurement system can be used to study the behavior of magnetic field variations around surface defects of ferromagnetic pipes. This system can be adapted to measure the position and damage level of small defects on the surface of ferromagnetic pipes.