Magnetic Domain Structure Research Articles

Microstructure and magnetic domain structure of additively manufactured Fe–Si soft magnetic alloys with 3 and 9 wt.-% Si

Electrical steels are numerously used in engineering applications. Nowadays, future challenges related to climate change and e-mobility push the boundaries to higher efficiency also in electrical parts. A promising material group to reduce electrical losses are electrical steels with high silicon contents. However, such steels are difficult to process with conventional methods and, thus, additive manufacturing came into focus in recent years. The present study investigates the processability, crack sensitivity, microstructure evolution and magnetic domain structures of laser powder bed fused Fe–Si alloys with 3 and 9 wt.-% Si. It is shown that specimens, which are built using appropriate process parameters, are dense and free of cracks. Still, Fe–9Si is characterized by a higher crack susceptibility at low temperatures of the build platform. A checkerboard like microstructure with elongated grains alongside build direction evolved. Global magnetic properties from ring core measurements showed lower losses for the Fe–9Si ring. Moreover, it was found that the magnetic domain structures are directly influenced by the crystallographic orientations present in the specimen volumes. The findings elaborated will contribute to advanced possibilities in tailoring the magnetic properties of electrical steels for an increase of the efficiency of envisaged applications.

Observation of zigzag domains in the surface layer of Fe-based microwires by magnetic force microscopy

The magnetic domain structure of the surface layer of Fe-based amorphous microwires with a diameter of 20 µm (after glass removal) was investigated. An approach has been developed to study the domain structure of the curved surface of a microwire by magnetic force microscopy. It was found that in low magnetic fields the domain structure of the surface layer consisted of zigzag-shaped domains elongated along the microwire axis. These domains are inclined to the microwire axis at an angle of 45 degrees. An increase in the magnetic field along the microwire axis resulted in the transformation of the magnetic structure to the structure consisting of ring domains with an opposite orientation of the magnetic moment. The geometric parameters of both types of the domain structure were determined. The width of zigzag-shaped domains was 2 µm. The width of ring domain was 2.5–5 µm.

Magnetic domain structure of iron-based microwires after removal of the glass shell by chipping and chemical etching

The magnetic domain structure of the surface of microwires with composition Fe73.9B13.2Si10.9C2 was studied by magnetic force microscopy. It has been found that the removal of glass shell by chipping leads to distortion of the original magnetic domain structure. Chemical etching of the glass shell makes it possible to observe the magnetic domain structure due to the stresses that have arisen due to the microwire production. In the absence of an applied magnetic field, a magnetic domain structure of the surface layer is observed, consisting of domain layers inclined to the microwire axis by 45 or 135 degrees. This structure has a shape close to a zigzag. The thickness of the domain layers is not constant and varies from 3 to 5 μm. It has been found that the application of a constant magnetic field along the microwire axis causes the formation of ring domain layers of various thicknesses (from 1 to 5 μm) with different orientations of the magnetic moment relative to the microwire surface. In a field of 60 oersteds along the axis of the microwire, the domain magnetic structure consists of only ring layers of domains. Magnetic field inversion leads to almost complete inversion of the observed domain structure. In this case, the complete removal of the magnetic field leads to the formation of a new domain structure of the surface layer. Such a structure is close in shape and position of the domains to the original one, but does not repeat it.

Evolution of tribo-magnetization during sliding of ferromagnetic materials

Sliding-induced subsurface microstructure evolution is believed to be decisive for determining the friction and wear performance of metallic contacts as well as the development of tribo-magnetization. This expects to develop a new prediction method of wear state by elucidating the correlation between subsurface microstructure evolution and corresponding magnetic domain changes. Herein, subsurface microstructure evolution including crystal and magnetic domain under tribological action is investigated experimentally. Our results demonstrate that dislocation mediated plastic deformation decisively influences microstructural changes during tribological contact, further determining the magnetic domain structure. Specifically, sliding-induced plastic deformation causes an increase in the width of magnetic domains, but depth-dependent derived microstructure formed under severe plastic deformation such as the refined grains and sub-grains, in turn, promoted the refinement of magnetic domains and their discontinuity, forming depth-dependent magnetic domain structure. These results are helpful to clarify the evolution of tribo-magnetization and the pinning effect of dislocations on magnetic domains.

Third harmonic generation microscopy of magnetic domains in garnet films

Nonlinear optical microscopy is a powerful non-destructive technique that allows to study a wide range of phenomena. Optical third harmonic generation (THG) is mostly known by its applications in investigation of biological structures, while magneto-optical effects in THG are not well recognized. Here we demonstrate high efficiency of the THG probe in studies of magnetic domain structure of epitaxial garnet films. We show that in spite of relatively small values of the magneto-optical effect at the THG wavelength, the THG microscopy may be efficient for the characterization of magnetic surface domains if the THG wavelength falls in the absorption band of a medium. Moreover, the in-depth sensitivity of this probe may be higher as compared to the case of the second harmonic generation microscopy.

Composition and microstructural control of Sm2Fe17N3 powders: a promising candidate for next-generation permanent magnets

The composition and microstructure control of Sm2Fe17N3 powders lays the foundation for the enhancement of magnetic properties, which is mainly ascribed to the optimization of the intrinsic magnetic properties and domain structure.

Research progress in the magnetic domain wall topology

Topological magnetic skyrmions, as information units, possess distinct advantages such as high reliability, enhanced integration, and low energy consumption. These novel topological characteristics offer critical material and technological support for the rapid development of information technology, 5G communication, and big data. However, the application of magnetic skyrmions in practical devices is severely impeded by certain limitations, including their stability dependence on magnetic field and the deflection caused by the skyrmion Hall effect under electric current. Consequently, exploring new topological magnetic domain structures and material systems suitable for application becomes a pivotal area of research. This paper primarily focuses on experimental studies utilizing high-resolution Lorentz transmission electron microscopy for <i>in situ</i> real-space observation and manipulation of topological merons and skyrmions inside the magnetic domain wall, confirming the theoretical prediction of magnetic domain wall skyrmions in 2013. We has firstly achieved topological meron chains inside the domain walls by using the spin reorientation transition in two-dimensional van der Waals Fe<sub>5–<i>x</i></sub>GeTe<sub>2</sub> magnets, and systematically studied the dynamic behavior of domain wall topological magnetic domain structures under external electric and magnetic fields, filling the blanks in this research area. The important and special roles of magnetic domain walls are revealed at the same time. Then the GdFeCo amorphous ferrimagnetic thin film was designed and prepared based on the summarized mechanism with the domain wall meron pairs successfully reproduced. Moreover, the reversible topological transformation from domain wall meron pair to domain wall skyrmions has also been realized without external magnetic field during spin reorientation transformation as temperature changing. The results of micromagnetic simulation and electric experiments on the topological domains in domain walls would provided a strong basis and support for the future research.

Variations in perpendicular magnetic and electrical transport properties of ferrimagnetic (0 0 1) NiCo2O4 films

We fabricated epitaxial NiCo2O4 films on (001) MgAl2O4 substrates by varying the pulsed-laser energy density from 1.31 to 2.46 J/cm2, while keeping all other parameters fixed. X-ray diffraction measurements revealed that the increase in energy density increased the film deposition rate from 0.022 to 0.078 nm/s, while resulting in the decrease of the full-width at half-maximum of the rocking curve and out-of-plane lattice constant. At room temperature, the films grown at an intermediate energy density range of 1.97–2.13 J/cm2 exhibited more distinctive perpendicular magnetic anisotropy and magnetic domain structure compared to those grown at high or low energy densities. On the other hand, the lower the laser energy density, the more pronounced the perpendicular magnetic anisotropy becomes at low temperatures. In addition, the ferrimagnetic-to-paramagnetic transition temperature of the film increased with the energy density, reaching a maximum of approximately 390 K at energy densities above 2.13 J/cm2. Furthermore, temperature-dependent resistivity indicated that the metallic behavior in the films grown above 2.13 J/cm2 was retained up to ∼ 500 K, which is much higher than the ferrimagnetic transition temperature. These results suggest that pulsed-laser energy density can serve as an alternative parameter for controlling the perpendicular magnetic properties and enhancing the metallic behavior of the (001) NiCo2O4 film.

Analysis on bimodal complex permeability spectrum of a noise suppression sheet and single constituent flakes

In recent years, highly integrated active components inside small mobile communication devices have led to serious electromagnetic interference problems. The countermeasure to this problem is covering a noise source with a noise suppression sheet (NSS) which is composed of ferromagnetic flakes and polymers. The NSS absorbs effectively electromagnetic waves due to a large imaginary part of relative permeability μr″ at the specific frequency region. This function is attributed to the bimodal μr″ spectrum of NSS, but its physical origin has not been revealed so far. In this study, the bimodal μr″ spectrum of NSS has been analyzed and its physical mechanism has been discussed. The μr″ spectrum of a constituent single magnetic flake was measured by using a newly developed high-sensitivity permeability measurement system, which showed a bimodal spectrum quite similar to that of NSS. This fact indicates that the physical origin of the bimodal μr″ spectrum is attributed to the magnetization dynamics of each single constituent flake. After measuring the μr″ spectra of single flakes with various materials, such as Fe, Fe-Al, Fe-Co-V, and Fe-Si-Al alloys, these bimodal μr″ spectra were quantitatively explained by the magnetization dynamics of the flux closure states inside the flake. The magnetic domain structure of a single flake was observed by a micro-beam X-ray magnetic circular dichroism microscopy. The result confirmed that the segmented magnetic domains form the local flux closure states inside the flake.

Investigation into the role of Co doping in the microstructure and magnetic characteristics of nanocrystalline Nd-Ce-La-Fe-B alloys

In this study, [Nd0.5(Ce0.5La0.5)0.5]17Fe78-xCoxB6 (x = 0 ∼ 1.5 at. %) ribbons are prepared via a direct melt-spun (wheel speed of 28 m/s). The impacts of Co doping on the crystal structure, Curie temperature Tc, magnetic parameters (Br, Hci and (BH)max) of [Nd0.5(Ce0.5La0.5)0.5]17Fe78-xCoxB6 alloys are systematically assessed. X-ray diffraction patterns and Rietveld refinement data demonstrate that the exclusive presence of a pure hard magnetic 2:14:1 phase without any secondary phases across all samples. Compared with Co-free sample (x = 0), the Br, Hci and (BH)max of Co-doped with x = 1 are increased by 15.0 %, 4.6 % and 42.9 %, respectively. The coercivity mechanism in the [Nd0.5(Ce0.5La0.5)0.5]17Fe78-xCoxB6 alloys arises from the integration of reversed domain nucleation and robust pinning of domain walls. The magnetic domain structure and quantitative analysis based on the microstructure and demagnetization behavior are conducted to investigate the exchange coupling interactions among the 2:14:1 grains. This exploration reveals that the enhanced magnetic properties stem from the refinement of the 2:14:1 phase's grains, leading to more uniform and smaller interaction domains.

Magnetic phase transition in dimer-based metal-organic frameworks through structural modulation

The flexibility of a structure is an important factor that affects the magnetic interactions, anisotropy, phase transitions, and domain structure of materials. It is essential to consider this factor for a thorough analysis of magnetic properties, as it enables researchers to design materials with specific magnetic characteristics for different purposes. In this work, experimental measurements were conducted to investigate the magnetic properties of DUT-8(Ni), composed of a Ni(II) dimer paddle wheel as the metal cluster and an organic linker. DUT-8(Ni) exhibits two distinct structures, one porous (open structure) and the other nonporous (closed structure), which have a significant impact on its magnetic properties. Our study focuses on the changes in its magnetic behavior due to these structural variations. The Ni(II) dimer's basic unit displays antiferromagnetic properties, and we observed interactions between intra- and inter-units in the 3D structure with the magnetic data we measured. To gain a deeper understanding, the magnetization of the open and closed structures is analyzed using a modified Langevin function.

Effects of drawing and tension stress annealing on the structure and magnetic properties of Co-based amorphous wire

Cold drawing significantly improves the size uniformity of the amorphous wire, but leads to wire curling. Tensile stress annealing (TSA) is the key to regulating the straightness and magnetic properties of Co-based amorphous wires, but their intrinsic correlation is still unclear. Herein, the effects of TSA on the morphology, microstructure, soft magnetic properties and longitudinal driven giant magneto-impedance (LD-GMI) effect of cold drawn Co-based amorphous wires have been studied in detail. It was found that increasing tensile stress can effectively straighten the drawn amorphous wire, yet at the cost of decreasing fracture strength, increasing coercivity and deteriorating GMI effect. Furthermore, appropriate annealing can restore the magnetic properties of the TSA amorphous wire. The variation of magnetic properties is relative to the change of circular anisotropic field and magnetic domain structure.

Studying the Crucial Physical Characteristics Related to Surface Roughness and Magnetic Domain Structure in CoFeSm Thin Films

This study investigated the effects of varying film thicknesses and annealing temperatures on the surface roughness and magnetic domain structure of CoFeSm thin films. The results revealed that as the film thickness increased, both the crystalline size and surface roughness decreased, leading to a reduction in coercivity (Hc) and improved magnetic contrast performance. Energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the presence of cobalt (Co), iron (Fe), and samarium (Sm) within the thin films. Notably, the 40 nm Co40Fe40Sm20 thin film annealed at 200 °C exhibited lower sheet resistance (Rs) and resistivity (ρ), indicating higher conductivity and a relatively higher maximum magnetic susceptibility (χac) at 50 Hz. These findings suggest that these films are well suited for low-frequency magnetic components due to their increased spin sensitivity. The 40 nm Co40Fe40Sm20 thin film, subjected to annealing at 200 °C, displayed a distinct stripe domain structure characterized by prominently contrasting dark and bright patterns. It exhibited the lowest Hc and the highest saturation magnetization (Ms), leading to a significant improvement in their soft magnetic properties. It is proposed that the surface roughness of the CoFeSm thin films plays a crucial role in shaping the magnetic properties of these thin magnetic films.

Microstructure, residual stress and magnetic properties of Tb0.27Dy0.73Fe1.95 alloy heat treated in high magnetic field

The directionally solidified Tb0.27Dy0.73Fe1.95 alloys were heat-treated without and with a 12 T high magnetic field. The changes of the Widmanstatten precipitates (WSPs), magnetic domain structure, residual stress, and magnetic properties during the heat treatment were investigated. The high magnetic field reduced the WSPs content and residual stress in the alloys. The effect of the high magnetic field becomes more obvious with increasing heat treatment temperature. The high magnetic field also changed the magnetic domain structure by promoting the alignment of the magnetic moments along the easy magnetization axis and increasing the width of the magnetic domains. The magnetization rate and magnetostrictive property of the alloys were improved by the decrease of the WSPs content and residual stress, as well as the change of the magnetic domain structure.

Effect of Mn Doping on Magnetic Properties, Magnetic Domain Structures, and Microstructures of 2–17 Type Sm–Co Magnets

Magnetic properties, magnetic domain structures and microstructures of Sm(Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.328</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.055</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.017</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bal</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7.65</sub> (x=0.005, 0.010) were investigated. Even with Mn content increased, magnetic properties didn’t deteriorate, remanent magnetic flux density, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , maximum energy product, [ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BH</i> ] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> and squareness, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> is a reverse magnetic field value when magnetization becomes 90 % of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ), exceeded 12 kG, 33.5 MGOe and 70 %, respectively in both samples. However, a mechanism of magnetic reversal was different, reverse magnetic domains were easy to propagate from grain boundaries in x=0.005, grain interior in x=0.010, respectively. In microstructures, Cu concentration increased in grain boundaries, and cell size enlarged with an increase in Mn content. Because microstructures were formed properly and its size was enlarged, which produce strong pinning force, and negative effects by doping non-ferromagnetic element Mn was compensated.

Magnetic Domain Observation of Milled Nanocrystalline Alloy Powder

Fe-based nanocrystalline alloys have high magnetic flux density and low loss. Therefore, in this study, the magnetic domain structure of the ball-milled magnetic powders of these nanocrystalline alloys was observed using a Kerr effect microscope. The effect of strain removal heat treatment on the magnetic properties of the powder was also investigated by observing and comparing the magnetic domain structure of the milled powder before and after heat treatment during the preparation process of the nanocrystalline-milled powder. Our findings showed that the strain removal heat treatment changed the size and shape of the magnetic domains to a simple structure. In addition, the domain wall motion was found to be sensitive to the magnetic field, resulting in soft magnetic properties.

Evolution of the domain structure in a FeNiCo nanowire under the action of a magnetic field

Based on the experimentally discovered domain structure and its evolution in an external magnetic field in thin films of FeNiCo composition with uniaxial anisotropy, a theoretical model of the magnetization distribution is proposed. The analytical dependence of the domain size on the magnitude of the magnetic field is obtained. The change in magnetoresistance because of the evolution of the magnetic domain structure is calculated.

Enhanced ferroelectric and magnetic properties of the 0–3 type BiFeO3-BaTiO3/BaFe12O19 composite multiferroic material

The 0–3 type (1-x)(0.75BiFeO3-0.25BaTiO3)/xBaFe12O19 (BFO-BTO/BaM) multiferroic composites were successfully prepared by a solid-state reaction sintering process. The coexistence of perovskite BFO-BTO phase and hexagonal BaM phase was confirmed for all BFO-BTO/BaM composites. Due to the large leakage current, the breakdown electric field decreased with increasing BaM content. Nevertheless, the ferroelectric properties of the composite ceramics have also been significantly improved, mainly as the increase of remanent polarization and the decrease of coercive field, where Pr = 19.79 μC/cm2, Ec = 30 kV/cm at x = 0.075. Meanwhile, the magnetic properties of BFO-BTO phase were enhanced, and the remanent magnetization linearly increased with increasing BaM content. The single domain magnetic structure was obtained for all BFO-BTO/BaM composite ceramics, and the magnetic properties changed after electric poling, which indicated the electric field controlled magnetic properties. The electric-controlled magnetic behavior was attributed to the structural phase transition. The magnetoelectric coupling coefficient αME of the composite material has been improved, with a maximum value of 0.61 mV/cm.Oe. Thus, the BFO-BTO/BaM magneto-electric composite system is a promising multiferroic system in information technology and sensing fields.

Optimization of magnetic domain structure and soft magnetic properties of FeCoNiGd medium-entropy alloys by gadolinium addition

Soft magnetic high-entropy alloys (HEAs) have attracted much attention due to their excellent mechanical properties and high electrical resistivity. However, the magnetic dilution caused by non-magnetic elements in HEAs greatly reduces their saturation magnetization (Ms). In this work, FeCoNiGdx medium-entropy alloys (MEAs) were prepared by adding gadolinium, a rare earth element with ferromagnetism near room temperature, into FeCoNi alloy to study its influence on the microstructure and magnetic properties. The results demonstrate that the addition of Gd can promote the precipitation of intermetallic compound phases in FeCoNi alloy. When x decreases from 1 to 0.5, the intermetallic compound phases change from GdM2 (M=Fe, Co, Ni) phase to GdM5 phase, and it becomes Gd2M17 phase if x ≤ 0.07. Moreover, the addition of a minor amount of Gd significantly optimizes the remanence (Br), while slightly worsens the saturation magnetization (Ms) and coercivity (Hc). Finally, the FeCoNiGd0.03 MEA achieves the best comprehensive magnetic properties with high Ms= 149.58 emu/g, low Hc= 434.3 A/m and Br= 0.231 mT owing to the high content of ferromagnetic elements and reasonable distribution of the magnetic domain structure. This work can provide insights into the role of rare earth elements on microstructure and magnetic properties of MEAs and HEAs.

Magnetic domain structure and magneto-transport properties of laser ablated Co40Fe40B20 thin films

We report the magnetic domain structure, and electrical and magnetoresistance properties of laser ablated Co40Fe40B20 (CoFeB) (6 to 36 nm) thin films deposited on SiO2 / Si(001) substrates. Magnetic force microscopy performed on annealed CoFeB thin films revealed larger magnetic domains, which are formed due to strong exchange coupling between the grains. The temperature-dependent sheet resistance of as-deposited thin films revealed that the observed non-metallic behavior is due to intragrain-tunneling and SiO2 inclusions in the amorphous matrix. The metallic behavior of annealed CoFeB thin films is due to electron scattering from grain boundaries and granularity correlated to the formation of nano-crystallites. Thickness and field-dependent magneto-transport studies show higher magnetoresistance values for thinner annealed CoFeB films due to more scattering events upon crystallization, which is consistent with the granular nature of the annealed thin films.